So I installed a new 3.5" powervalve and now the car wants to break up if i just slam the gas. If i lead into it raising the rpms slow she is fine. It has great throttle response from 2k up but from idle she sputters then takes off.

The car has a Holley 700 DP with auto tranny. I haven't been able to try it on the road to see if the sputter is worse or better, I have only ran it in the driveway.

 

Why did you put such a low PV in?

 

I'm pulling 5-6 in of vacuum. I have checked over and over for leaks and have none.

 

What are the details on the cam?

 

I have a 350 in my car with a Comp XE284H cam and I am pulling about 12" of vacuum. Your intake could be leaking from the bottom side. Usually a stumble or breaking up condition is cause from being to lean, again intake leaking.

 

I didn't have a stumble before I changed the secondary squiters, but at idle I'm running very rich. I changed my powervalve from the stock 6.5 thinking that was causing my rich condition.

My transition slots are perfect (double checked), my idle mixture screws are new with new gaskets, new carb-intake gasket.

When I was adjusting my mixture screws the best vacuum I could get was 6 inches. I also noticed that my vacuum line had a small kink in it so i will be fixing that before I continue tuning.

Duration
Advertised: Int 284° exh 296°
@ .050: Int 240° Exh 246°

Lift
Valve: Int .507 Exh .510
Lobe: Int .338 Exh .341

Timing @ .006"
Intake: Open 34° BTDC Closed 69° ABDC
Exhaust: Open 80° BBDC Closed 35° ATDC

Lobe Seperation: 110°

Intake Centerline: 106°

Cam is degreed in 1* retarded

 

Thats the same cam I have in my Chevette. My engine pulls 12" vacuum. I think the first thing I would do is try to improve the vacuum reading. I would check the plugs for oil on the threads. If you have oil on them the intake is leaking. Are you running vacuum advance? Timing at idle with the advance hooked up should be around 25°. This should help you vacuum reading. Did you go up or down in squiter size? Sounds like you just don't have enough pump shot if the only problem you are having is a stumble off idle.

 

Changing the shooter size or the PV shouldn't have affected your idle vacuum. I have a similar cam on a 109LSA in my 350 and I pull almost 12" at a 1000RPM idle. What intake do you have? Any spacer? Most importantly...tell us about the timing curve. 25* initial sounds about right to me. I have mine at 22* (15* mechanical). With vacuum advance hooked up, I have about 52* at idle.

The lean stumble sounds like not enough pump shot. What size shooter? What pump cam? Are you sure the pump arm and actuator are adjusted correctly (no excessive play, spring not compressing instead of moving pump arm, etc.)?

 

I have 16* initial and about 50* give or take full out. I went down in squiter size because I wanted to start with the carb at stock specs, went from 37 to 32

Im not sure on the pump cam but when i removed the carb to check it's transition slots I re-adjusted the pump cam arms to make sure they are set without any play but not too tight where they are pressing on the pump also the springs are not compressing when I whack the throttle.

I am running a 1" spacer with the 4 holes, Weiand Stealth High rise Dual plane intake. Heads are double hump ported and polished angle milled .030" bringing compression up to Static 11.2:1 Dynamic 8.3:1. No oil on the threads of the plugs except my number 8 but that is from my valve cover.

From everyone's advice I'm going to increase my squiter shot back up to 37, leave the lower powervalve in and bump my timing up 4 more degrees.


I think this covers everyone's questions.

Thanks again for the all help!
Chas