I finally got around to installing my Proform main body for my VS 750 Holley. Everything bolted up nice and smooth and the car started up fine with no leaks or anything. I had #68 primary jets in (which was just a tad rich with the stock main body) and was running very rich. I figured I would be running much leaner with the extra air flow I'm now getting. Anyway, I installed #66 jets and the car was perfect. NOW...

The throttle response is insanely good. When you floor it from a dead stop it just roasts the tires and takes off faster than it ever did but when you ease into the throttle or are cruising down the road it bogs down really bad. I power braked it in my garage and it stumbles right before it hits 1500RPM, drops down about 500RPM, then just revs like normal. Only bogs under light throttle below 1500RPM. Absolutely no black smoke, plugs all look good and it didnt do this with the stock main body.

Any ideas? First thing that comes to mind is accelerator pump? The car idles fine and WOT is great. It only bogs under load while reving slow or cruising.

 

Go the the Holley tech web site referenced in the sticky at the top of this forum. Read the part about selecting a power valve. After you follow those directions, let us know how it works.

If this happens as you slowly bring the RPMs up in a power-brake situation, but doesn't when you nail it, it can't be the accelerator pump.

 

Basically when I'm cruising down the road and give it light throttle to accelerate it stumbles. If I just nail the pedal to the floor it takes off like normal.

Before I installed the proform main body I had the exact opposite problem. If I floored it from a dead stop it would stumble and pop out of the carb. Now it does it when I'm NOT nailing it.

 

Your primary main jet is too lean. Go to #70 to 72
and solve your rich idle by working on the idle system not the mains. All it takes is a little dirt to keep the power valve off its
seat and cause a rich idle. Could also be a cross leak between the metering block and gasket.

 

At first I thought it was the power valve leaking but I turned the mixture screws all the way in and the car would not start ...so I figured it wasn't leaking from there. With the #68 jets in the car was pouring out black smoke even at idle. Floats are good and I used a vacuum gauge to set the idle mixture ...I'm starting to think that there MUST be a leak somewhere.

I'm going to take it apart after work today and clean out everything, make sure every screw is tight, and make sure every gasket is seated properly.

 

Black smoke, you definatley have an internal problem
normaly you could put in 85 jets in the primary side and although it would be quite rich, not rich enough for black smoke.

 

Well I took the bowls off today and cleaned everything off. I put in #70 jets and a brand new powervalve. Started the car up and it was giving off black smoke at idle but wasn't bogging down anymore. I took it down the road (clouds of smoke behind me), it was missing like crazy so I checked all the plugs. #2 and #6 completely fouled but all the other plugs looked perfectly fine. I put on new plugs and wires with no result.

I'm starting to think maybe I have a new problem ...stupid ignition.

Everytime I bolt something onto this car something else seems to go wrong the second I start it up ....Its cursed

 

Well I figured it out. I had 2 problems. I was fouling the #2 and #5 plugs because they were not gapped properly and I was also running very lean. Fixed the plugs and jetted up to #70 now the miss is almost completely gone. Jetting it a little richer should, I hope, completely get rid of it.

Thanks for all the help.