I have a holley 750 vacumm secondary on a zz430. The carb was set up by salle-chevrolet They put 71 jets in front and 73 in the back, also a light secondary spring. The motor pulls good to about 3700 rpms then it cuts out way bad and has a hard time accelerating. It only does it at Wot or near Wot, If I give it part throttle it wont miss but continues to smoothly increase in rpms.

 

I haven't had a Holley 750 apart for a while, but I seem to recall their having larger jets than that right out of the box. Even if it's running a little lean, though, it shouldn't be so lean that the car will bog. Do you have access to larger jets? If so, try 80s in front and 82s in back, just to see if that helps.

 

I think The carb is running out of fuel. I rechecked my timing and float level and took it for another run It pulled strong and I thought the problem was fixed. Then I tried it again and it surged and missed again. Do you think the pump in the tank isnt keeping up with the carb.

 

Unless you did a whole bunch of recent power mods, you shouldn't be suddenly overloading your fuel pump. When's the last time the fuel filter was replaced?

 

Top end fuel starvation is usually the reason for a miss or cutting out at WOT. I would try larger jets on the secondary side only, and also check the fuel pressure at WOT if you have the access to the right equipment. I am pushing 400HP on my Q-jet....so I know first hand about top end fuel starvation. Checking the fuel filter is a good idea as well...like metioned already. Pull a plug right after a WOT run and see if it is reading really rich or really lean, but my guess is a lean condition.

Oh yeah...the pump in the tank is not the best if it is the only thing supplying your ZZ4 than that could be the issue. I have an upgraded elelctric pump in my tank, and a mechanical holley pump up front, and have no more issues.

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Formerly known as 1984L69Z28

1984 Z28 - L69 optioned, 350HO w/ Trick Flow Heads, Drop Forged Lunati Crank, Crane Cam and 1.5 Roller Rockers, Stock Z28 Intake Manifold, Highly Tweaked Rochester Carb(700cfm), K&N Filter, ThermoMaster Chip w/ 160 Stat, Comp Headers, 3" Stainless Dual Exhaust w/ no Cat & Dynoflow Muffler, 4 wheel disc brakes, etc....

God bless us father, son, and holy ghost....whoever goes the fastest wins the most!!

[This message has been edited by 350HOZ28 (edited April 23, 2001).]

 

IM going to get rid of the pump in the tank and get me a inline Holley or Carter. I dont know which one is best yet. I will probably keep the regulator because the fuel line is about an inch away from the exhaust pipe and the circulating fuel wont vapor lock.

 

Could also try mounting an oxygen sensor (in-cab monitor, like Edelbrock's, $128 or so) in one of your header collectors to monitor while driving. It will help you figure out your problem and to better tune your carb for WOT, cruise, etc...

[This message has been edited by FastBroker (edited May 01, 2001).]