TQ Carb idle and stumble ????

[dodgit]

Hi Guys
I know I have read something about this before, but I can't seem to find it.
I have a freshly built 318, 1968 340 heads milled .060, Intake (matched to heads) is a mopar performance daul plane with a TQ on top (Not sure of cfm). I think a 340 purple shaft cam, right now only single exhaust with 340 manifolds. 904 slap stick tranny, 8 1/4 rearend with 323's and sure grip.
Orignal timming was supposed to be 2 deg and since I have had the timing from 2 to 14. It has helped and also hindered, But my problem is Very ruff and erratic idle. Also I have a stumble on initial throttle input. After that it seems to work well other than it sure howls when the 4 barrels cut in.
I have adjusted the idle numerous times and it seems like every time I do it the screw keeps going in further each time.
Also a real bitch when cold, but figure that is just the choke, But???
Please help. Just finished my project of 1 1/2 years, which is a 1972 Charger and wanta have sum fun. Very frustrating.

[amxauto-x]

try e-mailing demonsizzler here.

http://www.geocities.com/thermoquads/

he should be around here sooner or later to help as well as others.

[rumblefish360]

Off idle stumble? Check your pump shot. Air leak around the carb base?
Did you rebuild the carb? The umbrella is leather on some of the earlier rebuild kits and can shrink up. When that happens, the shot is weak.

If it's good, check the shot while the car is off. It should begin to squirt gas out at the slightest move instantly.

If that's good, perhaps your not getting enuff shot or to much shot. Reposistion the rod in another hole and rebend the metal rod arm to correct.

[dodgit]

Ok Thanks amxauto-x
I'll try that and maybe he will read this thread also.

[dodgit]

Thanks rumblefish. I'll try that with the rod, as it is shooting right off the bat, But maybe not enough.
Ok now what about the rough idle ????

[dodgit]

Thanks rumblefish. I'll try that with the rod, as it is shooting right off the bat, But maybe not enough.
Ok now what about the rough idle ????

[amxauto-x]

Rough idle could be all kinds of things. Check the following; spark plugs, timing, plug wires, idle mixture screws/settings. Dirt in the idle passageways in the carb. Dirty fuel filter/screens in the carb. Inline fuel filter clogging up.
What is the cylinder pressure? Have you done a pressure test yet? Or maybe a leakdown test? If the carb fixes doesn't take care of all the problems you may want to do these tests also.

[rumblefish360]

YA, what he said. AND, you didn't surply info that could be important to the ruff idle.
1st off, the comp. ratio exactly and the cam specs have a real lot to do with it. The cam should be known. Being a Purple cam, the centerline as advertised is on a 110. This will give a choppy idle. The Purple cams are ground more for performance than street idle quality's. Other Purple cams are ground on a 108 and installed on a 106. (I have used such a cam rated @ 288/.499 lift.)
This was a very ruff idle.
Valve lift with the duration also has a play.
The erratic idle is showing a vaccum pressure going up and down. This is drawing air and fuel out at different rates.
To much inital advance can also be a problem in conjuction with this. When the idle is low, it could be on the edge of advance. When it speeds up, (the rpm of the engine,) the advance kicks in and the engine surges.

I have seen 383 Road runners with some mild work still useing there OE Holley. Same problem. The fix was a pair of small holes drilled in the primary throrllte plate of the carb to allow more air in. I do not recomend this to you yet.
Speak to DemonSizzler first. He is VERY good with these carbs.
Tell'em we sent ya.

[amxauto-x]

What rumble said too

[dodgit]

Ok Guys thanks so much..!!!
I will try all of the things and will definitely post it here.
Until later.
Keep the shinny side up !!!

[Mister Fiberglass]

IF you have the larger TQ.....an 850 cfm(1 1/2 primaries) - that could be part of your "issues". Are you running a blocked exh crossover or open?

It is good that you are pleased with the WOT performance of this carb on your combo since it is sometimes a bummer tweaking a TQ to work on a smaller cubic inch motor.

[dodgit]

MR Fiberglass
It'an open crossover...
And for the cfm, I'm not sure, it was off a 340.

[DEMON SIZZLER]

Dodgit, if you can id the carb for us by reading the 4 digit part # stamped on the driver rear corner of the base plate.

Also a few things come to mind:
1)what style carb to intake base gasket did you use,
2)is the air cleaner a drop base,
3)be sure that the carb is not leaking down into the intake after you shut off the engine and also when the engine is idling, look for gas dribbling from the boosters and the 2ndary spray bars.
You should not see any of this.

If the primary jet sealing x style o-rings are bad, the carb will have a very 'rich' idle, so as suggested, check all spark plugs for fouling, DAVID.

[dodgit]

Hey Thanks Demon
I'll check it all out and get back to you with the carb #'s.
I used a Mr Gasket spacer/adapter.
And as for the Breather it is one off a 340 car, single snout and has the extra vacuum opening at the rear.
I'll check my plugs tonight, as I'm at work right now.

[dodgit]

Well as for the Carb #'s it is a 9207s.
The cam is a 284/480 with 210 deg (think this is right) 340 resto.
As for the compression ratio, not sure.. 1972 318 block with 1968 340 x heads milled .060. Flat top pistons.(maybe someone could help me figure this out) Because I don't know about deck height etc.
Somebody has mentioned to me maybe I over cammed the engine. Is this possible ????

Also I will do the comp and leak down test this weekend.
Anymore help would be really appreciated.
Thanks.

[DEMON SIZZLER]

Dodgit, your carb is a 1979 360 hd carb for a truck. It is the same one used on 79' model Lil' Red trucks and 3/4 ton trucks. It is for a smoger motor and will not run well on your non smoger engine
in it's stock state.

One thing you can try is:
fire off the engine and you can put two fingers down in the choke area to the inside of the front choke tower wall at the bottom and you will feel a vacuum. Keep these two holes covered and you will notice a drop in rpm's and the engine should smooth out. You can use a dab of epoxy over each hole to seal these.

I would find an earlier carb, pre 1975 or I can modify this one for you for best performance.

[drag-n-cuda]

DEMON SIZZLER,
Have you worked with Holley's in the past and found that an equally prepared TQ can kick arse over a Holley. Are you a current /former stock/ss racer? I've heard because of stringent rules, these guys are really focused experts on the components they have to work with.

drag-n

[DEMON SIZZLER]

Drag-n-cuda, I do like to drag race at the track(s)but I am not a known racer. I have built my T.Q.'s for 'class' racing with very good results

I built Holley carbs for locals from 1981-present, from stock to modified levels. I worked for Barry Grant(Demon Carburation Systems)last year as a carb technician for installers, racers and the general street racer and rebuilt/modified the carbs for customers while at BG.

In 1985, I was first exposed to ThermoQuads and started my interest in them. I eagerly recognized the potential of a T.Q. and
started my R&D to make these carbs 'competitive' with a similar cfm Holley. I was told by many sceptics, that these carbs were a waste of time; this made me even more determined to succeed and fueled the fire to turn these carbs into a serious power maker. I built 800 and 850 cfm carbs, mostly 1972-1974 pre smoger carbs, as a stock build through about 1990.

In 1992, I rebuilt my 340 with several upgrades, but the engine would not 'pull' until about 2,400 rpm's since it was a 292 duration cam/single plane intake. I did some thinking about this 850 cfm T.Q. and decided that I should really build a 'race' style carb for the engine and knowing that the 2ndaries were adjustable, I should be able to get the carb to make plenty of low-end power. Sure enough, after I completed the mods to the T.Q. , I was so surprised that this car would 'fry-the-tires' off!!!
The tork curve moved down to about 1,200 rpm's, the mid range power was really nice and the top end was wicked!! I gave these sceptics a ride one-by-one and they became believers!
I had to correct the 2ndary fuel metering and then, the engine was really BAD!

Anyway, at the present, I have added another T.Q. build for a very mild 318 and it is my 890 cfm race carb. I really like the exceptionally smooth idle and the fact that this carb gives the exhaust a killer, deep rumble much like a big block Mag engine.
In fact, it sounds like a hi compression 340. This carb has all the latest technology and will make a 318 look really racy and will perform likewise .

[rustycowl]

that 284/484 cam is alot of cam for a street driven 318 automatic. There probably are better combinations out there. Vacuum numbers? Can you advance the cam? Maybe that would help.
Use a degree wheel and dial the cam in. How far is the cam now from split overlap position? Try advancing it 4-6 deg from there(S/O).

[71SATELITE]

Dogit what kind of ignition are you using original points or electric? The points in my 71 had a horrible idle, also to low of an idle with that 14 BTDC will cause a harsh idle that is added to by the lumpy cam. It will give the carb all sorts of bad signals. Get a MP distributor and dial in the vacum advance and set your idle up to about 800 or 900 rpms and she will idle smooth with a small block. My 71 idles smoother than my wife's Furd expodition and will still rip the tires of on a launch!

[71SATELITE]

Sorry for the add on...David did you publish your book yet on TQ's? If not you should burn it on to CD's and sell them! I know a bunch of folks on here would wait in line for those, myself included!

[dodgit]

Well Thank You all !!
As you can see I'm just a rookie at this stuff, but willing to learn and of course it costs at the same time. So it really looks like my cam is too big. ( I'll have to live with it for a while)
I checked my plugs and they are almost pure white.....HOT and or lean... (right???) I brought my idle up to 850 and it sure did smooth out a lot. As for the stumble, it's still there. I tried the vacuum holes in the throat of the carb and didn't seem to do much. I think a lot of it is to do with my timing??? Not sure where to put it??? Before I built this thing the sticker on the car said 2 deg BTC. So with the cam where now??? I've had it high and low.
One more thing ??? Can anyone tell me what deck height is?? As I'm trying to figure out my comp. Ratio. And also if I have milled my 340x heads .060 what would my cc's be now???Somebody said that I might be getting close to the 10"s.
I know this is a lot, so thanks in advance and also very much for the previous help. One way or another I will get to melt pavement.
Thanks.

[71SATELITE]

Dogit go to the archive and type in mission ignition. It is very informative. Read it before you go any further. WHite plugs say lean but if you are running a hot ignition you will burn evrything off the plugs and it will constantly look like your moror is lean. Check it out and let us know how it turns out! Good luck.

[rumblefish360]

IMO, that 284/484 cam is a lot of cam not only for a 318, but the weight of the car combined with the 3.23 gears. Does your converter match the cam?
I beileve a smaller cam would be happier in there or a change of rear gears to 4.10's. Do a split duration cam. It'll help with the heavier car and 3.23's.

I had a bud run that within a 68 cuda. It was sluggish in the bottom RPM range.

[jasontlit]

I know I'm throwing another thing in to the mix, but...

My 340 had a slight "flat spot" off idle, and it turned out to be my stock 318 2 brl. distributor on my mild cammed 4 brl. 340.

A set of light springs took care of it. I made no other changes to the distributor,...yet. I'm sure recurving your distributor wouldn't hurt, if you haven't already adressed it.

[David Wiser]

I was having a lot of troubles with one of my TQ's and finally realized the holes for the air door pivot had way too much wear.
One was letting in extra gas when the secondaries open and the primary was leaking air at different rates depending on how hot the carb. gets.

[Rug_Trucker]

Yep David, we are waiting for the TQ book or CD!!

[DEMON SIZZLER]

As of the present, I am looking into the best way to put the info into print and will make my final decision soon. I have lots of illustrations and pics and loads of good reading too! I will keep everyone informed on my progress with the book, DAVID.

[b-1ken]

Check the intake to cylinder head seal. .060" is a lot of head milling. Spray some water near the manifold to head surface with the engine running and listen for a stumble or the water getting sucked in. If the leak is on the underside it may be difficult to detect. You might want to shoot propane (Bernzomatic) in there as well.