my holley runs rich while in gear & stopped. like smoke rich!
the stuff-
383
11.5:1/ iron eagle heads
crosswinds (super vic) intake
hookers
256/264@.050, 545/563 lift, 105 centerline (solid)
750 vac holley- all stock
3K coan converter
fuel pressure 7psi
the car runs fine, but if i get caught at a long light or a string of lights it smokes.

so far i've checked the float level (even have it a hair too low), tried a 4.5 power valve, played with mixture screws, just about everything. i've set the mixture screws with a vaccume guage, but it seems to run better with them out 1 3/4 to 2 turns.
i just tried putting the 6.5 powervalve back in out of frustration.

its all new, the motor maybe has 125 miles on it now, so i really doubt its anything defective or worn out.

any ideas?

 

Well,

I wish I could tell you an answer, but I don't know. However, I hope you get it figured out, cause I just bought a 750 Vac Sec Holley, and hope it doens't happen to me. Good Luck

BamaZ28

 

1 3/4 to 2 turns is way too much. I start at 1 1/4 and go in from there, usually ending up at 3/4 to 1 turn out.

That is a huge cam, but even more important, the lobe centerline is really tight ( I presume the centerline you refer to is lobe, not intake). I suspect all that duration and overlap (made worse by the 105 centerline) is pumping a bunch of exaust back into the intake tract, which is why you have to turn the screws so far out. It's no problem at higher rpm's, but at idle...

Engines with this problem can leave the intake ports black. 105 is great for a circle track engine, but something around 110 - 114 is probably better for an engine that is going to see traffic, especially with a lot of duration. JMHO

I ran a solid cam with about 250 duration on a 350 ( a Z28 offroad cam for the historians out there), but it had really wide centers, about 114 - 115 if memory serves. In a 4 - speed 57 Bel Air, it actually had pretty decent street manners.

 

Question, do you have to turn the idle screw way down to get the car to idle? If so you will need to pull the carb off and drill a hole in each of the front two throttle plates. This will let more air in while at the same rime allowing you to take some throttle (ie fuel) out of the idle screw. I had to do this on my 750 double pumper because my cam was really big. Chevy High Performance did an article on this several months ago. The following link wil show you what I am talking about.


http://www.chevyhiperformance.com/ed...=text&id=71498

Hope this helps

 

What amount of vacuum is your engine pulling at idle? If it's less than about 7" or so (which I'm sure it is with that cam) you probably have to put a weaker spring on your power valve. The power valve is designed to enrich the mixture when the manifold vacuum drops (IE: at full throttle). But if your cam is so healthy it's causing a severe lack of vacuum at idle, then you'll have to put a weaker spring on the power valve to keep it from opening at idle.

-Dave C. '97 Z28
454cid Gen VI