I am trying to get everything tuned in on my recently modified motor. I increased the jets on my holley 650 until i did not get a stumble on acc. like holley told me to. I now have 78's on the primary side. accel. is great, either wide open or part. The problem now is after accelerating and letting off part way it acts like it is running on 4 cylinders. Can anyone give me some advice?

350 gw bottom, 190cc al. heads, 650 holley, hei ignition.

 

After you do a fiew hard acceleration runs what do the plugs look like?
Also you did not say what the secondary jets are. How is your float levels high or low. If the secondary float is high then once you lift off a little on the gas fuel will slosh forward in the bowl and pull over into the boosters causing a flooding condition.

 

They are dark. I started out with stock and kept moving up per holley's instructions but now they are too big or i need to try a hotter plug.
Accel 576s on there now. I have not touched the sec. side, just changed the springs. I am gonna go check the floats after it cools down. Will the plug gap have any effect on that?

Thanks for the info. I'll let ya know if it works.

 

Well, there is 1 other thing that will cause it...... an unplugged vac. advance hose... It still isn't right but it is way better than before.

 

Ok a fiew other things to check. First is the advance mech in the dist moving freely. If it is sticking then by hooking the vacc advance line up you would see an improvement. Also 78's on the primary side is alot of jet. I would down jet them to 76. Also if your power valve is not proper for the car then you could also be fighting that too. Take a vaccum reading with the car idling in gear then split that number in 1/2. (if you have 12" at idle then a 6 inch pwr valve woulld be a good start.) Most 600 and 650 holleys have a 6.5 from the factory.
When you check the floats check them with the car running you want the fuel to just dribble out of the sight plug hole when you shake the car.

 

Throw out that carb and go EFI.

(That's the advice people generally give to EFI cars, thought I would try it myself - but in reverse).

 

Thanks for the info. I have been wondering about the power valve. I only have 9 in. of vac. so i will check to see which one came with it.
I think i need to go back to my air cooled vw's. I built a beetle that would run low 14's many years ago.

Hey reaper, if i had a couple thousand sitting around i would buy me a new holley efi system.

 

Actually, the stock EFI system is pretty darn good. I tuned a buddy's car that has a 383, AFR 195 Competion porting with 2.05/1.60, Miniram and solid roller 248/256* @.050. He's using the 1989 MAF system. That car runs with motorcycles and gets 25 US mpg on the freeway.

The later EFI systems for 3rd Gens are all fully understood now and easy to program. In fact, most guys who know how to tune a carb find tuning EFI even easier as you don't have even get out a wrench or screwdriver.

And because it's OEM, you can find it readily at wrecking yards quite inexpensively. SD would be the cheapest and if you have a stick, would be the best match. SD is faster reacting.

For simplicity of tuning, MAF works well (that is what my buddy has). The only expensive thing about MAF is the MAF sensor itself.

In the last five years we have learnt a tremendous amount about the EFI systems for 3rd Gens and obtain a state of tune that a carb can never obtain. And, there is even "reasonably priced" alternative intakes to the stock TPI (one of the reasons why many guys chose to switch to a carb). The Holley Stealth Ram is reasonably priced and one of the best "all-round" intakes available (and I own a Miniram).

If you have any questions, I'd be happy to answer them (and bring you back to the darkside).

 

oh wow, the Stealthram is only $300, that's news to me, I thought it was over a thousand.
You still need injectors, but I guess JY diving can get those right? What type of fuel rails are used?
Actually since that's not the topic, I may as well digress, and dig into some info on the TPI or other injection type of boards that I never frequent...

 

Sonix, yeah we shouldn't hijack this post. But if you ever do get into EFI, I live in Kamloops. Be glad to give you a "crash course".

PM me if you have questions.