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I have a small block Chevy 350 with single plane intake, Holley 750 double pumper, 50cc pump, 72 jets in the front & 73 jets in the back, squirters are 31 in front & 35 in back, a one inch adapter plate under carb. It falls on it's face at the line at full throttle, then it comes out of the bog and takes off & pulls good the rest of the way down the track. I am unsure of where to start adjusting to fix this, any suggestions?? Thank you.
OK, I dont have too much experiance with Holleys, but I do have a bit of experiance with carbs. If this was my carb, i would check the float bowl. Seems too high to me. Also, are the secondarys vacuum? Run a direct feed of the rear of the intake manifold, see if that helps.
CHECK FUEL PRESSURE AS WELL I HAVE SEEN THE FUEL PUMP CAUSE THIS PROBLEM BEFORE.MECHANICAL PUMPS DO THIS OFTEN IF ITS A STOCK PUMP.
without a doubt you need to step down the carb. You are running to much carb for to little hp. If you are pushing anything over about 400hp than I retract what I have just said. Anything less than 400hp will not be able to handle a 750. I would suggest a 600 or 650.
Just-speed
Rmayer;
Do you have a power valve in the rear float bowl? If you do, get rid of it and instead install a block off plug in it’s place, then install jets in the secondaries that are 6-8 sizes bigger than the front. So if you have 72's in the front, install 78s-80s in the rear. Run a size 65 power valve in the front metering block.
Next, get rid of the 50 cc pump and go back to 30 cc pumps. Install size 28 squirters in the rear, and leave the front at 31. Make sure that there is no slack in the adjustment arm to the accelerator pump.
You should be able to tune this puppy so that it seems as if it is fuel injected, smooth. Let me know! It would help if you let us know what cam and heads you are using as well.
RMayer, whats the max RPM you run this engine ?
Thank you to everyone who has posted suggestions. To help answer some questions, I run max RPM at 6500, I have a 515 inch lift Lunati cam, and 192 valve stock heads with 1.6 roller rockers. I appreciate the help!!! Thank you again.
RMayer. personally I think a 750 is a bit large, youd probaly be better off with a 670CFM vac. sec. or a 700 mech. sec..
As far as your spacer, is it an open, or 4 hole ? With that set up witha 750cfm carb, I think youd be better off with a 4hole spacer,other than that I think Typhoon is on the right track.