[gto70]

Help Guys! My car stinks(rich)like a Top Fueler at idle.Part throttle and WOT are OK according to my buddies chassis dyno air/fuel meter. Engine is as follows: .030" 455 w/ mildly ported 670's (238cfm In./185cfm Ex. @ 28"/H2O;Port matched Holley Street Dominator intake;Mighty Demon 825cfm carb.;Racer Brown(local cam grinder) flat tappet hyd. cam w/.510 lift In. and Ex., 242 duration @ .050 In. and Ex., LS is 108, LC is 105 In. and 111 Ex., non-bleed down lifters; 1.52 roller rockers; 10.0:1 comp. ratio; and some no-name 3-tube headers. The motor is installed in a full wt. '70 GTO and has run a best of 12.38 @ 109mph. I think the ET's are OK-though I've seen some on this site post equal to or better times w/more mild combos. It seems no matter how I adjust the carb. (it has replaceable idle air bleeds) the car just wants to idle rich. As soon as try I try to open up the air bleeds the idle falls off and I have to give it more fuel. Do some cars just idle rich due to lumpy cam specs? Does my cam appear to be too big for the rest of the combo? If so, any suggestions?
Help! Stinky

[gto70]

Help Guys! My car stinks(rich)like a Top Fueler at idle.Part throttle and WOT are OK according to my buddies chassis dyno air/fuel meter. Engine is as follows: .030" 455 w/ mildly ported 670's (238cfm In./185cfm Ex. @ 28"/H2O;Port matched Holley Street Dominator intake;Mighty Demon 825cfm carb.;Racer Brown(local cam grinder) flat tappet hyd. cam w/.510 lift In. and Ex., 242 duration @ .050 In. and Ex., LS is 108, LC is 105 In. and 111 Ex., non-bleed down lifters; 1.52 roller rockers; 10.0:1 comp. ratio; and some no-name 3-tube headers. The motor is installed in a full wt. '70 GTO and has run a best of 12.38 @ 109mph. I think the ET's are OK-though I've seen some on this site post equal to or better times w/more mild combos. It seems no matter how I adjust the carb. (it has replaceable idle air bleeds) the car just wants to idle rich. As soon as try I try to open up the air bleeds the idle falls off and I have to give it more fuel. Do some cars just idle rich due to lumpy cam specs? Does my cam appear to be too big for the rest of the combo? If so, any suggestions?
Help! Stinky

[KGTO]

Have you played with the inital timing at all? You can clean up some idle rich problems by advancing the initial timing. Also, some say, like Holley, to reduce fuel in the IFR (idle feed restriction) ports before changing air bleeds. I have use a piece of fine wire in these ports to limit fuel flow and it has worked. You are getting up there in cam duration to where you start to lose the "pull" required to signal the proper air to fuel at idle. At least thats been my experience [img]/infopop/emoticons/icon_wink.gif[/img]

1967 GTO 400 4-speed (416) #62's 11:1 solid lifter 6.8 Eagle/Ross 11.87@115 (w/mufflers)-->so far!

[cpetrice]

according to classicalpontiac.com 's compression calculator,your CR should be at least 11.25,not counting your deck height,or if your heads were milled. you did say 670 heads and 455 engine,right? I don't know if the higher Cr would make it run rich or not.

[Half-Inch Stud]

Three ideas :

Pull all eight plugs and verify an assortment of white and black plug tips. The white plugs correspond to Intake port leakage. How about pushrod press-in tube leakage too. Re-install your intake manifold to assure no leaks. Use Silicone Ultra-Gray, and let it setup&cure overnight.

Try a Q-Jet and see if the problem goes away.

after that,
Initlal timing in the high teens, with total advance at 34degrees....then perform tha carb adj.
Drive around and adj timing to negate any cruising ping.

H.I. Stud

"11.00/123MPH/1.50 60foot/29.5"/4.10:1/10"/472 #48/Flat HYD/DualQuad/Wenzler/3250Lbs
12.00/112MPH/1.61 60foot/26"/3.31:1/10"/472 #48/FlatHYD/Q-Jet/Torker/3650Lbs"

[gto70]

I haved tried advancing the timing all the way up to 20 degrees initial w/ no effect. Currently, my timing is set at 16 degrees initial and 35 total. I have tried smaller IFR's (changing a couple thousanths at a time)and only ended up leaning out the mixture which reduced idle quality. My compression ratio would be around 11.25:1 would it not be for the fact that I have dished pistons. 1/2", I do not believe that I have any intake leaks, all plugs show even coloration. I have also tried a q-jet with similar results. Thanx for all suggestions so far-please keep it coming. Any more thoughts around cam selection? Would Rhoads lifters or a comparable high-bleed lifter help to reduce effective duration/overlap?

[r hammons]

HAD THE SAME PROBLEM ON MY RACER, TRY LOCKING THE DIST AND RUNNING ABOUT 32 DEGREE TIMING AT ALL TIMES, THIS SOLVED MY PROBLEM ,WHAT THIS DOES IS GIVE YOU MORE TIMING AT IDLE TO LET THE ENGINE BURN THE FUEL , MY CAR WAS GAS FOULING PLUGS ABOUT EVERY 25 RUNS,

[Brian Baker]

Your problem is most likely from excessive overlap. I gotta' ask why the 108-lda for a relatively "mild" street/strip combo? With a 110 or 112 lda, you may find some lower ET's with your current combo. Rhoades lifters may help with the existing cam, but I would retard it 2 degrees from where you have it now with the Rhoades as they tend to advance the profile.

[Taff]

GTO70, do you have fuel dripping out of the booster venturis at idle? If so your primary throttle blades are open too far. There's two things you can do,first open the secondary throttle blades a slight amount-this will allow you to close the primaries to a point where the carb is running on the idle circuit not the intermediate circuit. You will then be able to use the idle mixture screws and throttle stop screw to adjust the idle speed. Secondly, you can advance the initial timing to a point where the car idles ,then read how much timing you have (it may be as much as 30deg) and then limit your TOTAL timing to 32-38deg or whatever you need. You will then be able to lower your idle speed and adjust with the mixture screws for a smooth idle. Oh, if you can't open the secondary throttles via a screw ,then you can drill one 1/8" hole in each primary throttle blade to allow more air in at idle and then adjust via the mixture screws .Hope this helps.

[gto70]

Guys, no fuel dripping out of the boosters at idle. I think I,ve pretty much come to the conclusion that no amount of tinkering with the carb. is going to give me the results that I am looking for. I may try running full advance (32-35 degrees) at idle and see if that helps. I have a MSD Pro Billet dist.-what is the best/easiest way to lock in full advance at idle.

[Torment]

Off topic but you'll pick up a bunch going to a 4 tube 1 3/4" into 3" header. I'd suggest your idle problem is in your carb and has nothing to do with cam specs, etc.. A hotter ignition(you didn't mention you had one) will clean up the idle. Also reference your power valve(s) to your idle vacuum if you haven't already.

The secret to happiness is not getting what you want but rather, wanting what you have.

[gto70]

Torment,I am going to change over to Hooker 1 3/4"
headers and 3" h-pipe and mufflers back to my
2 1/2" tailpipes. As for the ignition, I have an MSD 6AL w/ an aftermarket coil and an MSD Pro-Billet dist. Again guys, what is the easiest way to lock in full advance at idle and do you think that it will make a difference at the track?