Fighting with my carb/timing setup....

well, edelbrock says to set it at 16 degrees initial setting on the 302 performer rpm cam and heads to be "safe: Now, i know theres plenty more room, but haven't messed with it until i can get her to the dyno to see where my peak is...

its set at that 16 degrees, but with the 750 holley vacuum sec, shes running waaaay rich at idle. (ex - black smoke, eyes burning, etc.) also sneezing through the carb when shes cold. When she warms up however, it doesnt do it as bad, and seems to smooth out. The idle air/fuel mixtures are set right, main jet from 70 to 69 for our elevation. Now this is the carb holley and CHP told me to get since there will be nitrous on it after break in for track use occasionally.

any recommendations?

It's actually a 347 with the rpm airgap intake, rpm heads with 2.02 intake with a little work done, rpm cam to complete the edelbrock top end package (changed over from another cam)... 10.0:1 compression and a holley 4160 750 vacuum sec 4bbl. also the infamous doug thorley headers....

 

set the timeing to 32 degrees with the vac. advance line off and pluged with the rpm at 3000 rpm.
that will give you a good starting point. that 16 degrees doesnt make much sence.

 

i dont feel that you can acurately set jeting just by description and altitude. there are so many variables. on the 750 dp holeys they have 4 idle mixture screws. i ran one on a 351 and each one was bearly cracked off its seat to get it to idle correctly and not bog. i prefer to use the 700 cfm dp holeys on motors around this size just because it only has 2 idle speed screws.

 

I'll add my dos centavos.

Get a vacuum gauge and adjust timing and carburetor for maximum vacuum.

Hook the vac. gauge up directly to the manifold.

 

How much vacuum does it have at idle? Might be pulling in the power valve. I agree no book or directions will tell you what jet to run. I have a very mild 460 in my F100 and with the 3310-750 cfm carb I used to run on it I had 65 jets in it. It was still rich. I run a 600 now.
clint

 

idle

Sounds like your primaries may be too far open, you may be off the idle circuit. You should have the secondaries adjusted about .015 open . As noted above get the timing thing right first , then start messing with the carb. I also would wonder about the power valve. Holley puts out a pretty good tuning book available at most speed shops. Let us know what you do to solve the problem....

 

currently has 11 hg of vacuum at idle and im ordering the 5.5 or 55 power valve to swap out this week... i will adjust the timing accordingly and check my secondaries soon as my car gets back from paint... thanks for the tips so far...

 

sounds good

Yea - base timing first..its a constant, once set won't change. Then go to work on the carb issue. 5.5 PV sounds about right based on your vacuum readings. Open the secondaries until the transition slots are just barely exposed, then start working on the airbleeds using the vac guage, fronts first then secondary. Adjust for highest possible vac reading you can achieve. Where are you in Va?

 

THings is I bet those bleeds are not adjustable without drilling.
I bet the above author is right and his primaries are off the seats. Bet he needs to open the secondaries
11" ought not open a stock 6.5" power valve.
clint

 

20 mins north of Roanoke

 

thats how i adjust my idle mixture. once you get the highest vac possible, your there on your idle mixture. the rpm may go up or down as you adjust it, so turn it back to your desired rpm as you go. do each idle mixture screw a little bit at a time trying to keep them within 1/2 to a 1/4 turn of each other.

 

Hah, guess ill update this post from way back when lol.

The doug herbert GM Conversion distributor i was running was to blame. It never curved, and was junk from factory according to Terry Walters Racing Engines. they went to dial it in on their machine and noticed a binding inside the shaft. So, now im back to running a stock distributor with pertronix and had it dialed in and curved so that its all in by 3000. Trip to dyno this year should show a heckuva increase. Funny, i always seem to acquire the broken NEW parts.

 

He's got a 3310 vac sec 750. 2 idle screws.

 

soo ???????

Did that fix everything? Did you do anything to the carb? Fill us in please on the results.