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  #1  
Old 06-09-2000, 03:10 AM
DAVE JONES DAVE JONES is offline
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Question..... My vaccum reading at idle is aprox 13 at 1100 rpm. when I drop it in gear it goes down to 4.5 at 700 ropm. I cant give you a whole lot of accurate info on the motor since I bought It used from a chowder head. Its a 70 340 +.03 which I replaced the intake with a 6 pack setup. I dont know what cam (hydrolic) is in there now except that it has a .453 lift but I dont know the duration. The vaccum gage doesn't fluctuate at all, I've used spray and also a stethascope to listen for leaks and I dont feel that there are any vaccum leaks present. This 4.5 reading seems real low to me and from what I know of this its a real strong indicator of a heavy duration cam. I've adjusted the the pump cam and shooter as well as the 2ndary springs to get it to run the best that I can and there is no bog at wot or smoke. I also believe that I will need to change the 6.5 power valve down to a 4.0 for the carb to function properly. I tried to adjust my idle mix screws on the primarys but there is little difference in my vaccum. In fact it actually climbs a bit when they are all the way in which leads me to belive that my secondarys mix screws need adjusting. My neighbor beat me off the line with his lawn mower but I understand that since I'm running a stock torque converter and have 3.23 in the rear I'm not going to be any threat on the street.
Bottom line is......Is this vaccum reading normal and am I making the correct assumptions on the cam and carb above. Is this also an idicaton of the stall that I should be using. I read in another post that you can use the vaccum number and corrolate it with the necessary stall converter. Any input will be appreciated...thanks....

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  #2  
Old 06-09-2000, 05:06 AM
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pishta pishta is offline
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Wow, you must have one long cam, like 310 or more with vacuum numbers like that, lots of overlap. Get a 3.5 or 4 power valve, and check your idle set screw. If it is cranked down as much to expose the transfer slot, your idle screws are going to do nothing. I'de crack the secondaries with the idle screw just touching to get any idle, and start working the mix screws and idle screw to tune it. On a six pac, I gotta wonder if it makes a diffrence on which carb to crack, or does it have to be even? I wouldnt run a PCV valve either because with that low vacuum, it'll think you are at 1/2 throttle and always be open, even at idle. Not good. May want to run a header bung PCV setup, or run the PCV off ported vacuum. All else fails on the vacuum "leak" you think you have, relax all the valve springs and make 3 block off plates for the carb mounts. bolt em down with gaskets and apply vacuum to a manifold port. If it holds, your OK, if it doesnt, may want to look at the valves.
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  #3  
Old 06-09-2000, 05:01 PM
Hemi Mike Hemi Mike is offline
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Hate to answer a question with a question, but I might have a similar problem with my 360ci. but I havent gotten into diagnosing yet. Is this a sign of a cam that is not degreed in, maybe too far advanced? It's hard to believe that someone would put a 310* cam in a hot SB street car, but I guess anything's possible.

I'll bet that moving up to even a 2200rpm converter will make that rod burn the tires down the street from the red light!
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  #4  
Old 06-10-2000, 04:56 AM
mauve66 mauve66 is offline
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along the same lines, I went from astock cam to a hemi grind .474 purple shaft and had to drop to a 3.5 power valve to get it to idle in gear without dieing. Vacuum in nuetral was 12-13 but I never checked it in gear, duh! One thing I've learned from the six pak setup is that ANYTIME you mess with the center carb make sure the outers are unhooked and then re-adjust the linkage after your done setting the idle on the center one.
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  #5  
Old 06-10-2000, 05:31 AM
DAVE JONES DAVE JONES is offline
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Well, hears some some comments and question I have so far.
1..I always remove/uninstall the outboards
(2ndarys) before working on the center (primarys). I did this when I tweeked in my pump cam and shooter. I also did this when I worked on my idle mix screws. I also re-hooked up the 2ndarys to see if there was any change in the idle quality or vaccum and there wasnt any change at all.
2...Linkage to the outboards is set up perfectly. I always check that after any changes.
3...I run my pcv to the carb near the top where it is supposed to be attached.
4....I'm not sure what you mean by "cracking the secondarys. Unlike the idle mix screws on the primarys which are easy to get at, the secondarys have a plug from the factory over them openings and I would need to remove the outboards and remove the factory plug to adjust these. I have heard that this may be one of my problems but I havent attacked it yet.
5.... I do know that with a 6 pack It has been recommended to me by several good sources that alot of my idle problems (drop of 400-450) would go away with a higher stall. I'm thinking about going to a 2600 rpm stall. I do run a tranny cooler and as of now it stays cold.
6....I really dont think that I have a leak because of what I have done so far and the vaccum gage only varies about 1/2 max when its cold, warm, or hot. I believe that most vaccum leaks have a tendency to fluctuate during different temperatures and/or rpm's.
7...sounds to me that I need to change the power valve and up my stall to get this thing moving off the line. I am planning on rebuilding the moter and looking at a .557 lift with a 285 duration as well as some good heads..ie, 308, w2, w5, or some newer swirl ports. Thanks for the advice and ideas. I'm still open for more input if you have it as well as a good used set of heads. Let me know if you have any you want to get rid of or want to trade. I've got a nice polished alum torker with a 750 dbl pump. Thanks...DAVE

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  #6  
Old 06-10-2000, 08:30 AM
rat roaster rat roaster is offline
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What is your intial timing ? The mechanical advance along with some vacume could be in at 1100 rpm . Check your advance @ 700 rpm and @ 1100 rpm , when the idle drops back to 700, if the intial timing drops then its hard to get good vacume with a big cam. Big cams usually like an intial timing of 10 to 14 degrees and maybe a total of 35 . Set intial timing at 12 degrees @ 700 rpm and see how much vacume you have ,leave vacume advance off for now and plug hole naturally. If this helps recurve your distributor so you have 12 degrees at 700 rpm and 35 degrees (all in ) at 3000 rpm .This should be good for the street, next check your vacume advance maybe 50 degrees max at 3000 rpm ( including the 32 mech ) Crane makes an adjustable vacume advance kit. One of my favorite ways to check for a vacume leak is to slowly cover the carb with my hand and if the engine speed increases you have aleak the engine should slow down till it stalls the more you cover.I have seen 340 vacume @ 6 inches @ 700 rpm with a 474 /274 mp cam .I worked on a 340 that had a 508 /292 mp cam this car would die when you put it in gear with the stock distributor curve. I have also put a carb jet in the pcv to save vacume I believe a 72 .I have a great article as Im sure some of the others on here do to its called big cam blues , it steps you through tuning on a low vacume deal,if you want I can send it to you.
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  #7  
Old 06-10-2000, 06:46 PM
DAVE JONES DAVE JONES is offline
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I'd really appreciate it if you sent me the article. As far as my timing goes here is where I stand now. First, I dont run vaccum advance at all. I run strictly mechanical. I recurved my dist and welded up the slot completly and then remachined it. I currently have it set at 16 initial and 36 total. I have run it as high as 22 initial and 42 total. I have my dist set up pretty well so the initial stays there untill aprox 1200, then is fully kicked in at 1800. When I have changed the timing I checked vaccum and nothing changed between the 2 that I mentioned above. I have run my vaccum and got the timing to aprox 55 with my inital set at 12-14. I still dont see any change in the vaccum. Just so you know....when I say there is no change I am comparing the same rpm so I'm comparing apples to apples. obviously when the rpm goes up during idle, so does the vaccum. I also have checked for any hidden vccum leaks with the hand over the carb check and it responds correctly, the rpm slowly drops till I stall it out.
Thanks for the input...I'm still all ears for any other ideas.

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  #8  
Old 06-10-2000, 08:20 PM
moparsofcamelot moparsofcamelot is offline
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I have a 440 6pack. Spent a couple months last summer making adjusments. What I finally
did was crack the thottle body screws on the outboard carbs 1/4 turn counter clockwise and reajusted center carb. Things improved alot.
I think you said yours are plugged. You have to remove the rear carb to adjust throttle body screws anyway. During all of this I washed out the center carb's gasket
to intake with fuel. It had major damage to gasket which caused vaccum leaks. Check it after you crack
outboard carbs. I have 17 at 900rpm in park and 14 in drive. Good luck.

[This message has been edited by moparsofcamelot (edited June 10, 2000).]

[This message has been edited by moparsofcamelot (edited June 10, 2000).]
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  #9  
Old 06-11-2000, 02:56 AM
DAVE JONES DAVE JONES is offline
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When you are refering to "cracking the throttle body screws" are you refering to the idle mix screws?. I'm assuming you are and I'll try it. I have heard that this does help if the idle mix screws on the center carb dont seem to function properly.

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  #10  
Old 06-13-2000, 02:39 AM
hemigtx hemigtx is offline
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DaveJones! Hello again. I re-learned something at the track Saturday regarding six packs (actually Holleys in general). I've always fought a vacuum leak on one of my set-ups. Determined that the throttle shaft was HORRIFICALLY sloppy on the center carb and pretty bad on the outboards. Don't know why I never noticed that before...I bought this set-up used, and am going to have the throttle shafts bushed. I remember you saying that yours are used as well. This might be something to look at. Go with a lower power valve, as you mentioned. Keep us posted!
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  #11  
Old 06-14-2000, 12:59 AM
DAVE JONES DAVE JONES is offline
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Thanks Hemigtx. It makes a lot of sense. I do have some slop in that shaft but I tried spraying around there and didnt see any difference. Maybe since I cant hit both sides at once there is no difference in rpm. Try not to laugh but since I'm idleing maybe I should try some putty around the shafts and see what happens to my reading. The main reason that I still dont think that is my problem is that I get at least 12 in idle at 1150 and In gear it drops to 4-5 at 650.
I dont know if this info helps but I also notice that after about 20 mins it seems like my idle gets even lower when I drop it into gear which it almost wants to stall. That probably another problem but Im still all ears. Thanks for the advise...DAVE

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  #12  
Old 06-14-2000, 07:21 AM
BThompson BThompson is offline
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It seems to me when your idle speed is cut in half by putting the car in gear your vacuum signal is also cut in half. On a properly tuned motor vacuum is affected by three things idle speed,timing and leaks. My 440 with .540 lift and 268@.050 idles in park at 1200 and 6in of vacuum, in gear it idles at 900 and 3.5in of vacuum. The convertor stall is 3500. My 340 with .504 lift 223@.050 in park at 800rpm pulls 16in. havent checked it in gear. Sounds like a vacuum leak to me. Cant see a .450 lift cam with that much duration.
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  #13  
Old 06-14-2000, 08:59 PM
hemigtx hemigtx is offline
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The way I figured out that my shafts are worn out is that the idle speed changed dramatically when I pushed the shaft around (I was very careful to ensure that the blades stayed closed). I could actually hear the hiss of the leak. Mine is so bad it's worse than leaving a vacuum line unplugged! I think BThompson had some good input there...
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  #14  
Old 06-15-2000, 10:02 PM
moparsofcamelot moparsofcamelot is offline
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There are no mixture screws on the outboard carbs. The throttle plate has 2 screws for each outboard carb facing toward the front. Your screws have plugs covering them. New carbs are not plugged so you can see them. Are your carbs 69/70 stuff? Is your engine a 340 or 440? Also, I worked my way down starting with a 6.5, 5.5, to a 3.5 power valve.

[This message has been edited by moparsofcamelot (edited June 15, 2000).]
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  #15  
Old 06-16-2000, 01:47 AM
DAVE JONES DAVE JONES is offline
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I've got a 1970 340 with a 70 6 pack out of an AAR. My screws are covered. sounds like I used the wrong termanology regarding the 2ndarys idle mix screws. I do know that you can adjust these and I heard that they
MAY play a role in the idle mix for the center....primarys if the primary idle mix screws dont react at all. Am I totally in the weeds or starting to get out?

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  #16  
Old 06-17-2000, 07:55 PM
moparsofcamelot moparsofcamelot is offline
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You have used carbs and probably not have been rebuilt. That can be tough to figure out problem. Start with power valve. I don't know what cam you have but the overlap will decrease vacumn and a high number power valve like a 6.5 which comes with most Holleys will let additional fuel dump down the intake at idle. Not good. Get a 3.5 and if it doesn't run out of fuel at top end you're ok. If it does move up to a 4.5. But carbs as old as yours without a rebuild kit probably needs to be rebuilt.
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  #17  
Old 06-17-2000, 09:10 PM
DAVE JONES DAVE JONES is offline
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Well, checked to make sure that there was no leak at the shafts (used putty. No vaccum drop or fluctuation at all. I also followed your advise and dropped my curb idle speed very low. Then my idle mix screws started to react a little and I was able to gain another 1" of vaccum. I'm also sure that right now my power valve is doing me no justice at all but that will change. My friend that I got the 6 pack from is a real Mopar freak and excellent mechanic. He completly rebuilt all the carbs from top to bottom. He came over to double check to make sure that everything was in proper working order. He pretty much says that with my setup and cam that I have now, There is no choice but to get a stall converter (which by the way he has recommended to me 100 times now)....aprox 2600 stall. From what he says and you guys say it seems like that is the missing ingrediant. I know with a looser stall converter my rpm wont drop as much and keep my vaccum higher and give me better idle quality. After I put this in I'll see what my vaccum is in gear at idle. Only then I'll change my power valve if necessary to get it to where it should be. Thanks again for all your help.

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  #18  
Old 06-18-2000, 09:04 AM
Sancho301 Sancho301 is offline
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Dave,
Since you're looking for wild stabs, & since your motor was built by a chowder-head (been there, done that, huh?) have you checked your cam timing? Wonder if maybe the dude got confused by all them keyways & funny marks & stuff & just slammed it together? Took me quite awhile to centerline the cam in my 440, & I'm not stupid. Well, not extra-stupid, anyway. Isky claims that lift should be pretty equal at TDC ON OVERLAP, which makes a pretty easy quick-check deal. At least with straight-grind cams. Might be worth a look, at least.
G'luck,
Scott
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  #19  
Old 06-18-2000, 03:47 PM
DAVE JONES DAVE JONES is offline
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Thanks Scott, I went into the front end of the motor when I got it and found that the marks didnt line up by 1 tooth. I fixed this and made sure that that at least the cam was in the straight up position so I could at least base line the pig. I didnt want to change too many things in there at the same time. I still think that since I have no idea what is in this engine or heads since I havent torn it down yet I think my best bet before I do any other major decisions is to wait till this winter for a tear down and rebuild. I am sure that no matter what that I should do the gears and stall now since I know what I want to end up with. I dont have a problem doing something now that I want to end up with irregardless of what I find in the inside. I'm sure that I will be changing alot of the internals and I'll also be going to the 308 heads. Thanks again....DAVE

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  #20  
Old 06-18-2000, 09:24 PM
moparsofcamelot moparsofcamelot is offline
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Dave Jones, are you getting email today?
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