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Old 07-29-2002, 01:43 PM
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cuda66273 cuda66273 is offline
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Default How to: 4 Corner carb adjustment?????????

I continually see posts referencing carb adjustment problems, rough idle, rich idle and
general confusion on these four corner carbs. Probably some of you have even stayed
away from these great carbs for fear of trying to figure out all the screws and
adjustments.
Have no fear Grasshopper, it's not a big deal and the end result is
awesome.

I have a few minutes here this morning and after reading another such post I thought
I'd share this with Ya'll.


So as clear as I can explain it with my 10th grade education and having failed English 101,
here goes my best shot....

Carb adjustment

Let's use my favorite, a 750 Race Demon with 4-corner idle and full mechanical linkage as an example here
the others are similar and some of this theory can be applied even if they only have a 2 corner
idle system.

Here we go.....

Start out by putting a small piece of paper between the throttle butterfly adjusting
screws (Idle screws) and the stops, let the throttle close, now back off the idle screw until
you can just slide the paper out, now go back in 1/8th of a turn. Do this on both
primary and secondary ends.

Now screw in all four corner air mixture screws until they bottom and back out 1.5
turns.

Hold the throttle open a little and start the engine, now ease the throttle to the stops,
if it tries to stall DO NOT hit the throttle, tap gently on the accelerator pump arm…. did
it get better or worse?

This has told us what we need to know, if it got worse your still rich and you need to
go 1/8th of a turn in on the idle screws. If it got better the opposite is true, so you'd
obviously open the idle circuit an 1/8th of a turn as your engine is looking for more fuel.


This may take several times around the carb to get it right.

Oh the paper…well, there'll always be air flowing around the butterflies and remember
you bumped the idle up 1/8th of a turn. If you still can't get the idle speed you want
adjust each idle screw by 1/8th of a turn until you get the desired idle RPM, but you should be real close at this point.

Just remember…whatever you do to one idle screw do to the other, keep track of exactly
how many turns you have on the idle screws and write it all down.

It usually takes me anywhere from 45 minutes to an hour to balance a four corner carb,
be patient the end result will be quick and clean throttle response with a smooth, odor
free and crisp idle.

So now the theory part, pay attention here they will be a test later...LOL

The idle cucuit basically just dumps fuel and relies on the velocity (remember this word) of the air flowing around the butterflies to atomize the fuel(another big word) so your engine can burn it efficiently. If you have too little velocity or the butterflies are open too far, the fuel will not be atomized correctly and raw fuel will be sitting in your manifold and in extreme conditions on your piston.

So the velocity is critical for a smooth idle and crisp throttle response. It's all a matter of getting the correct volume and velocity to match the correct amount of fuel being dripped into the engine by the idle mixture screws.

Betchya didn't realize that the idle speed screws were such a critical part of the tune up did you?

OK so now you've got it running smooth, set the timing and start all over...hahahahaa...and you thought this was gonna be quick and easy

Depending on what cam your running, but on a solid lifter small block like I have with restrictors in the oiling system I like to keep my idle up around 1200 to be sure that the cam is getting plenty of oil splashed up on it, your preference may vary...it's just an anal thing I do left over from my old alcohol sprint car days.

This is still confusing? ... post a question and I'll try to clarify it.

Next week we'll talk about reading the "timing" mark on spark plugs...betchya didn't know you could set the ignition timing in each individual cylinder by looking at the spark plug did you?

This is chapter 8 is in my soon not to be published book...Mopar Tuning for Dummy's ...written by one.....LOL

Until next week......this is Cuda66 saying goodnight for "Mopar Mystery's"

Part 2-Power Valve Tuning

OK the long awaited part two in this continuing saga is finally here:

Power Valve…. What the heck is that?

Let's first of all look at the function of the power valve…when you initially stomp the
throttle open the front end of the carb is running 8 jet sizes smaller (right?) so it needs to
catch up to the rear…we'll explain this off balance situation in a moment.

If you look at a metering block where the P/V screws in, you'll see two tiny holes, these are
called the "Power Valve Channel Restrictors", big name for a couple of little holes. This is
where the fuel dumps through the power valve to richen the front half of the carb when you
smack the throttle. Remember what I said about the 8 size smaller jets in the front?…well
the "Power Valve Channel Restrictors" dump fuel through the valve at a rate equal to a #8
jet which gives you the balance we're looking for…so the big question? Will a Holley power
valve work in your BG carb?
I don't know as I don't have a Holley P/V to compare it to or can I find any specs on the
efficiency rating of a Holley P/V…but you know I have this gut feeling that they're probably
not quite the same. So lets say you don't have the required 8 size split in the front
side…..your going to have a lot of problems getting it to transition from the idle circuit to
the primary circuits properly resulting in a hesitation or stumble. Having the incorrect jet
split will cause the front and rear sides to operate at different A/Fuel ratios especially
during the transition.


The correct way to determine the optimum vacuum rating of the power valve is to first hook
up your trusty vacuum gauge to the lower or below the throttle plate spud, now fire it off
and drop it in gear….. You'll probably see a reading of 6-12 depending on the amount of
overlap on your cam for this example we'll use 8. This is of course after you have everything
else set correctly in the idle circuits and timing.

The formula is 1.0 to 1.5 below idle in gear vacuum, so we would use a 6.5 power valve in
this case. This is the correct method and you should not vary from it.

I want to address some idle questions that have been filling my email box, one of the
major problems in getting your performance engine to idle is lack of idle timing a high
compression engine with a big cam needs timing to burn the required amount of fuel to
make it run. Don't expect your hot small block to idle at 900 with 10 degrees of initial
timing in it, it just won't happen. You need about 25 to 30 degrees of initial timing to
enable the engine to burn the fuel efficiently and not drip it out the collector. To test this
theory if your having problems getting it to idle using my instructions in Part 1 and try
advancing the timing at idle up to about 25 and then give it a try, you'll find the idle speed
will jump way up…why? You didn't give it any more air or fuel??? Your now burning all the
fuel, so now idle down and do your four corner adjustment …you'll now have that crisp
snappy throttle response that we we're looking for off idle.

CAUTION!!!!!!!
This is ONLY a TEST you cannot run your engine this way you'll end up with 50 degrees of
max timing if your distributor is not curved correctly and catastrophic failure or death may
occur.

Ok so now we've got the idle circuits adjusted, the idle timing set correctly, just snap the
throttle a bit and you'll see that that hesitation is gone and you'll get the urge to take it
for a asphalt ripping test drive…stop! see previous paragraph.

When you go to the distributor shop and tell him you want 25 initial and 38 max at 2200
he's going to look at you funny……he's just used to Holley's and Edelbrock's and there
insensitive idle circuit and transition technology.

HOT TIP:
For you drag racers looking for that bottom end tork to annihilate your 60' times, stick a 1"-
4 (FOUR HOLE) spacer under your Demon.

Next chapter we'll talk about nozzle extensions, critical fuel velocity, wet flow Vs. dry flow,
accelerator pump cams and maybe more. I'll explain how and why a 750 Mighty Demon
540-2010GC flows at 930CFM on the Holley tester….you won't believe it!

How about a bigger carb that will actually lean your motor down…..

When we're done here you'll all be experts and able to tune your Mopar to the optimum
with ease at any altitude………..

This is Cuda66 for Mopar Mystery's…. soon available in paperback….well, maybe copy
paper….


Rich idle condition

NOTE: the order of the solution or cure to this problem has been Changed....sorry I wasn't
thinking straight this morning


Rich Idle adjustment procedure:

I've heard several stories of rich idle conditions and have encountered this problem myself
although not to the extent of some reports.

This is a totally curable condition and can be easily accomplished by the racer at home with
a minimum of tools.

Before any of these modifications are attempted the following must be checked.

1. Correct initial or idle timing.
2. Correct idle speed adjustment
3. Correct adjustment procedure of 4 corner idle screws
4. Correct octane level for engine
5. Correct fuel flow and pressure
6. Correct float level
7. Correct carb size for engine
8. Correct internal circuit operation of carb
9. No fuel should be dripping from the boosters.
10. The enrichment screws are less than ¾ to a 1/2 turn from the bottom or closed
position.

If you are confident that all of the above are checked and double-checked you may want to
try the following procedures to cure the rich idle condition.

2. 4 small holes .060 or so may be drilled in the butterfly's to allow more air in the manifold
at idle.

3. Increase the holes to a max of .080


1. Depending on which carb you have there are 4 small holes in the top of the carb main
body that allow air into the idle circuit. These holes can be opened up with a #50 drill bit,
which is .070 in diameter.
The existing holes in a Speed Demon for example are .059 primary and .063 secondary, by
opening up these air holes you will effectively increase the airflow to the idle circuit.
The carb should be disassembled to just the main body and special care must be taken to
be sure that no drill chips get into the circuitry. I use a hand drill and turn the carb body
upside down, then blow it clear with carb cleaner and air pressure.


I have found that by drilling the butterfly's 90% of this condition can be cured and before I
open up the air bleed I always check and be sure that nothing has blocked them.

That's your "Carb 101" lesson for today, hope this helps.

This information is based solely on the Authors personal experiences and not to be
assumed that the manufacturers of any Carb recommend them, always consult with the
manufacturer before making any modifications to your carburetor.

Depends, Edelbrock, Speed Demon and any other products mentioned here are for
comparative purposes only and their mention is no way to be construed as an endorsement
of their products...unless of course they send me money which I always need.


I think I should also add here that the carb is sensitive to the signals that are given
through the venturi's and cam duration, overlap and lift are critical in selecting the correct
carb.

NEVER EVER select a carb soley based on the size of your motor or the HP you expect to
make, you'll usually be disappointed or at the least the engine will not perform to it's
maximum potential.

If I suggest a 750 Mighty Demon at $495 don't think that the $725.00 750 Race Demon DR
will be better, it won't.

The internal design of a Demon carb is specific to a certain range of signals generated by
the engine at various engine speeds and unless you have done 15 years of research and
have the computer spread sheet to make the proper carb selection..ask an expert..and
that's not the tech line at some mail order house.

I don't care where you buy it....from me, Smummit or anywhere else, but ask me what to
buy, or..a fool and his money will soon be parted ...as they say.....


Response to Holley problems:

Without knowing what type of Holley's your running It's real hard to say what the problem
is.

The power valve opens when the engine vacuum drops below the P/V rating, so a 6.5 power
valve won't open untill the engine vacuum drops to 6.5 or lower, if the power valve is too
small you'll usually get a stumble on launch as the primary's will be lean.

The same thing can happen in the secondary's if the G forces push the fuel back in the bowl
and uncover the jets, the cure for this would be jet extentions and a notched float kit.

Rich idle condition is caused by either too much fuel or not enough air, this is where your
gonna have to do some diagnostic work to find out which....take the carb back to Hollley's
recommmended baseline setting and work from there, if it was a Demon it would be easier
for me to help you as I have all the engineering info and can walk you through the changes
to clean it up....there is no waiting time on my tech line ....I answer the phone....If, I can
hear it over the roar of whatever scream
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  #2  
Old 07-29-2002, 02:21 PM
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Default Thank You!

I will go through this process and see if it helps my car from falling flat on its face. (Off idle stumble)

In the past when I adjust Idle speed/mixture I shoot for the highest manifold vacuum reading I can get. This usually works fine, however, not this time. Where would using a vacuum gage fit into your process, or do you not recommend using one?

I gotta tell you, I really wish YOU were consulted when the instruction sheets for these carbs were writen. I learned more from your posts on this board than reading and re-reading all the carter/holley/demon books and install instructions I've aquired over the past 20 years! I'd put money down on your book any day!

Demon Specific Question: When is it absolutly necessary to pop in those "Air Bleed" inserts? I fear we may have poped 2 of these in our carb a little early (Lean Idle). After reading your post, I would like to pop them out and start over! (Have you ever done this?)

Later!
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Old 07-29-2002, 02:50 PM
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cuda66273 cuda66273 is offline
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Well thanks for the compliments...I'll forward your response to my old english teacher...LOL

Definately pull the idle plugs and start over...I've never had to use them.

I'll use a vacuum guage on a Edelbrock or stock type carb that doesn't have the engineering to allow for each venturi to be adjusted separately. your best manifold vacuum is really just an indication of the highest velocity that can be achieved before the idle goes rich.

I will go into jetting some other time but for now be sure that your 2 sizes bigger on the secondary's, no more and no less.

That's where we start, then we adjust the four corners to compensate for poor manifold flow to each pair of cylinders...you wanna go fast and never melt a piston......stay tuned

Be careful when reading your plugs, with the fine adjustments on a Demon a lean condition can easily be mistaken for a plug thats too hot, I did this and ended up with HUGE jets and still had white plugs.....put a colder plug in and dropped 8 jet sizes...Duh....picked up 2 tenths...

If you ever get to a National NHRA event stop by early in the morning or skip a round and spent it with my Buddy Richard Hicks from Barry Grant, they always have a tent set up somewhere near the ProStock Boy's...(HUmm I wonder why they are always near them guy's) Richard can dial you in in 5 minutes what would take me weeks on this board to do..he wants my book too....lol

The Book.....well over that past several months when I get into these technical discussions here I've been saving the postings and my answers to a file....it's actually getting pretty big. Maybe someday I'll print it all out and offer it for sale...when I need new tires ...LOL......$1.00 a copy divided by $430.00...humm do you think I could sell 430 copies?

BTW all you members ...rate this post for me...just curious how many are interested in this high tech stuff?
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Old 07-29-2002, 05:09 PM
dynorad dynorad is offline
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Default

I live for high tech stuff.
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Old 07-29-2002, 10:47 PM
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Thumbs up

Cuda,

Keep the tech posts coming ... I love this stuff!
Gonna tweak my Holley's idle screws this weekend.

BTW, What do you recommend for tuning the cruise and power enrichment circuits on Holley's? As I recall, someone used to make a kit that allowed you to install tiny Mikuni carb jets in the metering block power valve channel restrictions to allow for independent tuning of these two circuits ... I haven't been able to locate any current info, though.

D
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Old 07-29-2002, 11:37 PM
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"BTW, What do you recommend for tuning the cruise and power enrichment circuits on Holley's?"

I reccommend a Demon, the BG Pros have already done it and done it right.

"independent tuning of these two circuits"

That's new one on me....but hey, I'm a racer...I drive a Fird F150 all week, never had a cruiser.

I wish I could tell you all sorts of great Holley tech tips but I've spent the last 7 years working with the BG Guy's and I've barely kept up with all their changes and improvements. You wouldn't believe all the hours I've spent talking to and learning from their experts and track testing their carbs...come to think of it, I don't recall ever owning a Holley Carb....it's always been Kinsler Injection or BG.

I went over my 750 tonight and I got the idle screws down to 1/4th of a turn into the stops with a 1500 RPM idle speed you wanna hear crisp throttle response! Whap! sounds like my old 410 Outlaw Sprinter, it took about an hour to get it perfect.
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Old 07-30-2002, 12:03 AM
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Oh great yeah sure thanks a lot. Now I have to go get a 4 corner carb to see what I been missing out on. Even though I dont have one yet.... It is still good reading. Looking forward to the igntion article.
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Old 07-30-2002, 12:07 AM
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wow

Phenominal....you, sir, are phenominal. I printed the post and don't even HAVE a 4-corner adjustable carb! 440cj
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Old 07-30-2002, 12:11 AM
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This is great! I was just thinking of my BG 625 Street Demon's 4 corner idle. Ill send you a crisp Washington if you can get me in the ballpark with my carb's jetting! I feel I have a great carb, but I cant get it to run any better than my 20 buck Pomona AFB. Maybe you can Email me when you get a few minutes.

pishta68@hotmail.com
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Old 07-30-2002, 12:31 AM
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does the ofset of '2' for frt and rear jetting apply for a holley also? and do demon's use power valves or are they plugged off
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Old 07-30-2002, 02:25 AM
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Default RogerH there's a message for you here...

Jeeze Guy's easy...I'll never get my helmut on this weekend...

rigsy: The Holley's are not machined to the same accurate spec as the BG Carbs, the main differances are the Billet metering blocks, center sections and float bowls which eliminate perosity.

It's just common sense that you can be more accurate with a block of billet, CNC machined than you can be by trying to cast in the circuits.

2 jet sizes on a Holley carb is probably a reasonable starting point but if you want to super tune your Holley I would suggest the "Holley Tuning Book" available at most speed shops for about $40.00 and ...good luck.

Pishta: Send me all you base engine specs, gear ratio, tire size, weight with driver, manifold spec, base timing and max timing at what RPM, hook up a vacuum gauge and give me the idle vacuum and I'll get you close. Then we'll send you down a dozen or so jets to play with until we get it right on, once we get you dialed, return what you don't use and all your originals for the next Mopar brother. If you have Holley jets don't worry I send them back to BG and they replace them with new BG jets.

I've been field tuning BG's on my own for several years, they're great people and appreciate what I do in the field...my pay is a full box of new jets every year which I in turn give away free to racers on a "New Jet's for Old" program.

Once you get set up and dialed in...DO NOT EVER SWAP A JET WITH A HOLLEY...they flat do not flow the same and you'll screw up a good tune-up, order your jets from BG and accept no substitution an 85 Holley is about equal to a 80-82 BG but the Holley's vary so much it's impossible to make up a cross over chart....keep the dead president...you'll need it for tires, just drop an email to Jerry Dooley at BG and thank them for supporting the jet program...oh ya maybe mention my name so they know I'm still out here working for them...

440cj...someday you will

RB77413....when your ready I have the source for the smokin' brother-in-law deal

You'll enjoy the Mission Ignition article I'm working on...I pulled one of my plugs today and it told me:
1. My initial advance was about 4 degrees low.
2. My max advance was also short
3. The 64 plugs are way better than the 66's
4. The cylinder temps got too high last Saturday.
5. #2-3 are running richer than #6-8
6. I drank too much coffee this morning
7. After 90 passes it was time to tune up the old fish...that's right haven't touched the tune up for 90 passes! and still ran 9 passes on Sat. within 7 thousands of a second with temp variations of 74 to 88 degrees.

You Guy's with Holley's please, this is not a slam I'm only relating my experience with what I feel are great carb's that are sometimes intimidating and confusing. You just can't be an expert on everything so I find what I believe to be good stuff, study on it with a vengence and try and pass on the knowledge.

RogerH:
I'm pretty dam good on your Edelbrocks too....tuned one last week...car went from a best of 16.21 to 15.87..a tweek here a tweek there a metering rod change and a couple of springs I had laying around.....zoom! Of course if I had a nice box of rods, springs and jets I could probably make a bunch of your customers alot happier campers....hint hint

Of course a trip to the factory for a Edelbrock Carbs 101 course wouldn't hurt...Motel 6 would be fine and I'm available right after the Div 6 Finals in Yakima....

Ok so here's the legal stuff my lawyer buddy wants me to add…just read it real fast.

This information is intended to be a guideline for strip and or off road applications, the information provided is the express opinion of the author who is in no way affiliated with or employed by BG Carbs, any of it's associates, dealers, shareholders, employees, vendors or affiliates, and is to be interpreted as a personal opinion based on personal experience only.

I will presume that all 17,000 members have now read this and I won't have to type it again
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Old 07-30-2002, 02:29 AM
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rigsey: my fellow Canadian Buddy...sorry I missed that Powervalve question...yes they use a power valve, maybe tommorrow I'll learn Ya'll a thang or three about Powervalve tuning and maybe some float level stuff...if I have time....
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Old 07-30-2002, 11:32 AM
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Well, beleive it or not, an Edelbrock carb isn't even handled by us. Weber, now Magneti Marelli, makes all the carbs and we just market and sell them.

If you think you have some nice stuff to tune up a carb, I'd say your best bet would be to talk to the tech line guys, or specificlly ask for Smitty. That, or email Vic, he gets all kinds of product advise! You should see some of the hair brained stuff that gets sent in!
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Old 07-30-2002, 01:37 PM
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"If you think you have some nice stuff to tune up a carb"

No, you guy's have all the nice stuff....most of your customers buy an Edelbrock carb and bolt it on with little or no adjusting. What I've found is most of them need to be tuned although your book is excellent you need to have some basic carb knowledge which alot of people just don't have.

They need help, you guy's are along way from the action way out here in Oregon. The local distributor, Performance Warehouse, has some competant Guy's but there not much help when it comes to dialing in a carb at the track.

If you Guy's were to hook me up like BG has I could really help you in the field keeping your customers happy and improve your sales, this would cost you only a supply of small parts and gaskets...what a deal! You get all the credit I do all the work, make cars go faster and I get to see all those big smiles

It probably costs BG about $50.00 a year and I probably spend 100 hours tuning carbs for them.

Print this out and slip it onto Vic's desk for me
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Old 07-30-2002, 03:15 PM
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I'm interested in your plug reading technique. Did you pull the plug more than once or did you divine all of that from pulling it once?
How do figure that stuff out?
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Old 07-30-2002, 04:24 PM
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I used to be pretty good at setting up Carter AFBs, and I realize that the calibration is all different on the edelbrock/weber carbs, but wouldn't the tuning be similar? The reason I ask is that I have a pair of old carter Comp series 500 AFBs on an Offy dual quad intake on my 400 in the '48 pickup (not on the road yet) and I wonder if it would be worth swapping to a set of edelbrocks, or even a pair of demons (would have to put them sideways, but it sute would look cool). We ran this setup before and always had some problems getting it idle cleanly, but it would pull like a freight train right from idle. I know I could go faster easier with a single four, but I have this retro look going with the finned Offy valve covers, the dual AFBs and all. I haven't been into cars very heavily for a few years now (wife, house, job you know how it is) so your plain english tech is waking up some of the passion I used to have for tuning. let me know what you think and thanks for the post.
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Old 07-30-2002, 04:42 PM
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Dyno:
I'll try and explain the plug theorys in my Mission Ignition post in a few days.

Some plug read info I can understand and other stuff seems to be alot of hocus pocus that someone has come up with while sniffing NoX. I'll try sort it all out and see which ones are fact and which ones are flashback hallucinations from the 60's.

The coffee thing I'm sure of, that whiskey I drank sure didn't make me shake like that.

When I checked with my timing light...sure enough the max advance was at 32 degrees.....and just for grins I checked it at idle...sure enough 7 degrees...we're now at 37 total at 3000, so the theroy on plug gap Vs. timing indicators on the porcelin seems to be correct.
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Old 07-30-2002, 05:02 PM
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Default How do I figure this stuff out?

God gave me two ears and one mouth so I always try and listen twice as much as I talk.

I've been around the racing curcuit for along time and I've learned tips and tricks from some of the best. I've worked on Outlaw teams, owned my own Outlaw Sprinter, run with the WoO boys off and on for a few years, worked with Joe Cantrell co-founder of the original Die-Hard Racing (Now Robert Yates Racing), spent time with Ray Ally in a top fuel pit, Pit Crewed on WC cars, Formula Ford, ProMod, my Buddy owns a NHRA A/F funny car, my cars have won local track Championships from Texas to Oregon...I listen, I learn and try to remember, which is the hardest part.

A Great Racer once told me... "If you can't beat him, quit whinning and just get better. Learn from the Guy's who whip you every week, they obviously know something you don't and you better find out or be happy with second best"

I'd sure like to strap the old fish down on your dyno, lock the doors and spend about 20 hours tuning that thing.....I'll bet we could find another 50 HP.
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Old 07-30-2002, 07:12 PM
dhochsprung dhochsprung is offline
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Cuda,

I find your postings very helpful compared to some of the Holley books I have been reading. I have been trying to eliminate poor idling on my 600 cfm Holley without success. I will be looking forward to your future postings. I am also interested in how to read plugs.

Thanks for the help
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Old 07-30-2002, 09:48 PM
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RogerH RogerH is offline
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cuda.....

Hehe...I think I misunderstood what you were trying to hint at me! You know....busy day...skimming the thread....blah...blah...

When I get back to work tomorrow I will read it more and show it around. I am not very knowledgable about carbs. I am into EFI systems a lot. I do know it is an art to tune a carb, which is why I like EFI a lot....but then I am from the young computer generation! ....and while I like hot rods a lot, I also like them little rice burners!



Roger
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Old 07-30-2002, 10:58 PM
moparman318 moparman318 is offline
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Cuda, Man I wish I had a guy like you sitting in my garage right now. I have talked to a dozen different mechanics and none of them can tell me what is wrong with my truck. After reading your posts I picked up a few things and now have a carb question. Is it possible that the 600 edelbrock on my 318 is running rich at idle but lean when I am cruising down the highway. I was told a lean engine heats up, but mine runs rich at idle, and overheats. Basically, is it possible that a carb could be causing my truck to overheat.

Also, I really like the look and features of the demon series carbs. Maybe I will use one on my project truck when I get out of boot camp.(USMC ) Would you prefer a holley/demon style carb or a edelbrock/carter style for a 4X4. To tell you the truth I think that anything stamped Edelbrock needs to be SH** on and lit ablaze.
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Old 07-31-2002, 12:34 AM
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rb77413 rb77413 is offline
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Quote:
Originally posted by moparman318
Cuda, Man I wish I had a guy like you sitting in my garage right now. I have talked to a dozen different mechanics and none of them can tell me what is wrong with my truck. After reading your posts I picked up a few things and now have a carb question. Is it possible that the 600 edelbrock on my 318 is running rich at idle but lean when I am cruising down the highway. I was told a lean engine heats up, but mine runs rich at idle, and overheats. Basically, is it possible that a carb could be causing my truck to overheat.

Also, I really like the look and features of the demon series carbs. Maybe I will use one on my project truck when I get out of boot camp.(USMC ) Would you prefer a holley/demon style carb or a edelbrock/carter style for a 4X4. To tell you the truth I think that anything stamped Edelbrock needs to be SH** on and lit ablaze.
Not jumping on anyones toes but I am going to throw in i an idea because I had the same thing happen after a cam swap. It just ran rich and overheated when before the cam swap it ran fineminus the flat lobe The fix: Timing was really retarded. However it started up fine. Checking the timing as a just in case. The carb I have is an Edelbrock 750 with the elec choke.
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  #23  
Old 07-31-2002, 05:35 AM
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cuda66273 cuda66273 is offline
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Default OK so maybe this should have been a separate post....Ed .....go ahead and move it

Now Now Moparman318 lets not $hit on anything that doesn't look like a shingle....

"running rich at idle but lean when I am cruising
down the highway"

Yes, lets look at a metering rod and the Edelbrock idle curcuits and how they work together..bear with me it's late I'm free typing this post so I may have to repost some other time but I'll try to give an better understanding of how it all works.

Idle srews: control only the fuel mixture at Idle and have little or nothing directly related to the cruising or WOT position of your foot.

Metering rods: there is two diameters on the rods and if you look at them close you'll be able to see the two steps on the rod.

Jets: for simple tuning the jet is just a variable to give you a more finite adjustment of the metering rods.

Lesson 2.....

"You need Bigger Metering Rods to get more fuel" if someone says this to you, RUN! as far away and as quickley as possible, never let this person near your carb with anything other than a polishing cloth for the air cleaner lid.

"Wire those wieghts open"...just pull out your gun and shoot this stupid SOB, he's too stupid to own a car.

"Try putting that vacuum hose for the distributor on the bottom nipple"...send him somwhere to a farm to look at real nipples he has no Idea what he's talking about...if he picks up a screwdriver get the sawzall out and cut his hand off.

Lesson 3....

Never let anyone touch your carb, learn how it works and what to adjust and when, to get the result your looking for...unless... this big, fat, bald headed guy with a dirty old Dodge hat on walks up and asks..."Need some help..." don't even answer just hand him the tool box, listen and watch....and he likes that green Poweraid stuff during the day...at night it's ET (Early Times) and Pepsi..no Coke, Pepsi Pepsi....

Ok so here we go, get out your note pads and there will be homework err ahh trackwork for ya'll this weekend.

You'll need a vacuum gauge, not a good one, I got mine at Baxter's here in town for $9.95.

Plug the gauge on the lower port on the front of the carb, this should NOT have your vacuum advance unit hooked to it.....right? Ok

Now lets get the idle down as low as it'll go without stalling, now start turning one of the idle screws in until it starts to loose vacuum or the engine starts to sputter, write down that number.....now count the turns as you turn the screw out until the same thing happens. lets say your number is 2 so now go in 1/2 of that or 1 right....OK now same with the other side.

Now start all over again..Idle, in, out, count and set.

By now you should have a pretty good smooth idle easy huh....

Now lets watch the vacuum gauge 1/2 turn in 1/2 turn out slowly turn the screw back and forth no more than a 1/2 turn in either direction until you get the highest reading on your gauge, thats it your done.....runs good now doesn't it.....set the idle up to your desired RPM for most of you using a Edelbrock your probably running a pretty mild engine so 750-950 is probably about right.

Now crack the throttle off idle...sounds pretty good huh :-))

OK now check your timing and set it where you want it.

Start over and do the whole process again...Idle down..the old in and out...vacuum gauge and now your done.

Secondary circuit...

This is where you need the karma of the Skuza's monkey.

Grab a couple of new spark plugs and a wrench, we're going on a road test. Find a nice lonely road somewhere, install a new plug in any hole that's easy. Now stand on that throttle run it all the way through first and about 1000 RPM below your shift point in second, turn off the key and release the throttle at the same time. Coast to a stop and remove the new plug, is the porcelin black brown or white?

Brown is good and probably good to go on the other hand if the plug is white it's lean and if it's black it's rich. We just tested the WOT mixture and we now have a baseline on that end of it.

OK put in that other new plug, this time drive the car hard but do not let the secondary's open, you may want to leave the air cleaner off so you can hear the carb working and keep it off that deep howl that the secondary's make when they open. This time run it all the way up to your max RPM and shut down the same way. Pull the plug and install one of your old ones and head for the shop.

Remember the two different diameters on the metering rods. The rods are pulled up out of the jets as you accelerate, the first stage or primary circuit is the larger diameter of the metering rod, the smaller diametyer or the tip size is your secondary or WOT circuit.

So let's think about this...the SMALLER the diameter of rod the more fuel right....remember the rod is lifted out of the jet and because it's thinner at the end as it's pulled up and out of the jet seat, more fuel is allowed to flow into the engine....make sense?

For this example we'll use a metering rod numbered 40/60, 40 being the tip of course.

So let's say for example the #1 plug in our plug test was a little dark brown almost black and the # 2 test plug is almost white. By our test we know that #1 plug was wide open throttle so our engine needs less fuel at WOT so the smaller number of 40 needs to increased to say a 45.

But, the primary throttle circuit is showing a lean condition so it needs more fuel..so...yup, you guy's are smart, we would drop it to say a 55 so now we need to go looking for a set of metering rods 45/55. and start all over with a couple of new plugs and back to the road.

This is how I do it and to super tune one of these carbs you really need a spark plug reader and look way down at the bottom of the porcelin but for most simple applications this will get you so close you'll never feel any improvement in the seat of your pants.

I used this method 2 weeks ago on my neighbors 80 El Camino (sorry but someone has to keep them running or they'd be cluttering up all the roads)

It's a basic stock 305 last winter we put a Edelbrock RPM manifold, 600 Edelbrock, curved the distributor, headers and he tuned it up to the best of his ability...it ran 16.40's pretty consistantly but always had a stumble and was hard starting. I got tired of hearing him crank and crank the thing and convinced him to let me tune the carb...it didn't take much convincing....last week the car ran 15.87, 15.91, 15.88 and broke out in the 1st round with a 15.87 on a 15.88 dial :-((

He checked the milage and it picked up from 14.4 to 18.2! Not important to me but he liked it.

There's alot more fine points to these carbs but my fingers are tired and I need to get my ugly sleep. Besides you have lots to work on for now...

Next lesson we'll discuss:
What those springs that the metering rods sit on do and .....what are those weights and how do they work?

How about Secondary circuit timing, accelerator pumps and more.....

Goodnight boys and girls....this IS cuda66 for "Mopar Mystery's" bringing Mo-Power to ya.

See ya'll at Mission Raceways August 8-9-10...I might even take a pass in that blown 440 Cuda we're bringing.....good thing I got some "Depends" for my 50th Birthday.....

Oh ya almost forgot...

Depends, Edelbrock and any other products mentioned here are for comparitive puposes only and their mention is no way to be constude as an endorsement of their products...unless of course they send me money which I always need
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Old 07-31-2002, 05:49 AM
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So there you go Roger...more mail for Vic's desk..hint hint hint.....got it...wink wink.

Good night ZZZZzzzZZZZZzzzzzZZzzzZZzzZZzz
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  #25  
Old 07-31-2002, 08:47 AM
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AAR4fun AAR4fun is offline
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Why is it Holley guys say you can't get the performance from a Demon and Demon guys say you can't get the performance from a Holley?

I ran across a Holley guy who professionally builds his own carbs from bulk castings he purchases from Holley. This guy actually came recommended from Dave Koffel. He swears by Holley and swears at Demon.

Jeez, are they not basically the same design?!?

Some of us are just standing in the middle looking confused. duh...
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Old 07-31-2002, 11:47 AM
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cuda66273 cuda66273 is offline
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"professionally builds his own carbs from bulk castings he purchases from Holley"

So why doesn't he just buy one already built from Holley???????

I guess you gotta put a check mark on the Demon side here....they work right out of the box...now that you know how to adjust them.

Holley makes a nice piece and they work great, I think that Demon has just gone one step further and perfected a good basic design.

When I cruise the ads in National Dragster, Mopar Performance and others I see ads everywhere for re-worked Holley's proclaiming better flow, more power blah blah blah....I have yet to see an ad for anyone re-working the Demons...so what does that tell you???

"Some of us are just standing in the middle looking confused"

You think the carb stuff is confusing, search cam shafts on Google....LOL
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Old 07-31-2002, 12:54 PM
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AAR4fun AAR4fun is offline
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Proves my point... You are much pro Demon.

Personnally it matters not to me one way or another. Knowing what to do with the hardware and tuning it is the key. As you have pointed out.

I just found it an entertaining observation how passionate folks are when talking about Demon vs Holley when they are very similar in design.

Thanks for the great write-up.
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Old 07-31-2002, 01:52 PM
moparman318 moparman318 is offline
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Two quick things:
Cuda- great writeup and thanks that will really helpnarrow down the prob. If I get tune this thing like ya say and get better milage and all I think I should send you some of the gas I won't be needing.

Rb77413- Was your valve timing or ignition timing retarded?Right now my ignition is set at 8* so i don't think thats to much of a problem considering it was at 14-16* and still overheated. If it's valve timing your talking about I will haul a$$ down to the nearest mopar speedshop or what ever and get the offset cam key to compensate or be a cheap a$$ and roll the timing chain or something.

Thanks for all the help. This forum as a whole is great and I want to thank everyone in all the forums for any help they give me.
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Old 07-31-2002, 02:13 PM
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cuda66273 cuda66273 is offline
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Default Barry Grant program

Dear Moparians.....

Our BG fuel deal is in jeopardy, my good friend and main contact at BG has moved on to greener pastures and I have lost my main contact there.

If any of you own or plan on purchasing a BG fuel product and my postings have in any way helped in the tuning or decision process on your upcoming purchase would you mind taking a few minutes and dropping a quick email to:

tech-sales@barrygrant.com
Attention Scott and/or Jerry

Would you mind CC'ing me a copy...thanks
cuda66273@hotmail.com

Just a one line email expressing the value of my posts here would be great.

Do you think we can fill their email box?

Thanks Guy's I owe ya one....
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Old 07-31-2002, 02:17 PM
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cuda66273 cuda66273 is offline
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Moparman318: Yes please mail that gas to me I need it for that hog Motorhome....LOL

Lemme know how it goes.
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