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Old 08-12-2007, 10:53 PM
thelastdon15's Avatar
79 trans am w/ sbc
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holley double pumper problem

This is kind of long. I have a chevy 350 with a holley double pumper with mechanical choke(i believe its 700cfm but im not sure). Anyway, i had a bad bogging problem from a dead stop. I was told by my dad that it may be the accelerator pump and or discharge nozzles. I went larger and seen no diffrence. Eventually i bought a 50cc kit and installed a 45. It started and reved up great. My brother noticed a leak where the fuel line connected to the carb so i turned it off and tightened it. After that i tried to start it and it would have difficulty starting and when it did fire...it would only fire on a few cylinders it seemed. I kept trying to start it and it did the same thing over and over. Then out of no where it started up and i could gradually rev it fully. I could turn it off and start it with no prob. A week later i tried to start it again but it had the same problem as before. I tried switching to the old size discharge nozzle with no sucess. Any ideas? Would apprieciate any help.

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Old 08-13-2007, 12:50 AM
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It sounds like it`s flooding. When you go to start it hold the accelerator to the floor, if it starts up and runs rough and few seconds and clears up, it`s flooding.
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Old 08-13-2007, 05:55 AM
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Ill give that a try. Thanks for responding.
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Old 08-13-2007, 06:28 AM
Will I ever get it done?

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I believe in a systematic approach to Holley carbs. First, do you have a high quality, high flow filter in the fuel line, preferably immediately before the carb? If you don't, get one. Next, do you know what the fuel pressure is at the carb while the engine is running? Much over 7 psi and you will flood. Much under 5 psi and you will starve. Look down into the carb. You will see 8 bleed holes. Are they clean? If not, a quick shot of carb cleaner should take care of them. If they are severely blocked, you may have to disassemble and clean. A high quality air filter will cut down on maintenance in this area. Once you are sure you have good clean fuel at the correct pressure, you need to set the float levels. A double pumper should have sight plugs and externally adjustable floats. Have a fire extinguisher handy. Start the engine and let it warm up. Pull the sight plug. Loosen the lock nut on the needle/seat assembly and adjust the seat up or down until the fuel is just about to dribble out of the sight hole. Lock it down and replace the plug. Repeat the process on the other bowl. Now adjust your accelerator pump linkages. With the throttle plates fully closed, you want to make sure you have no clearance between any of the contact points in the accelerator pump linkages. You want to adjust the spring loaded screw until you just remove the slop. If you put too much pre-load on them, you can reduce the accelerator pump output or even damage the pump diaphragm. Once you have all of this done, it should run pretty good. From here, check to make sure you have the proper power valve and you will probably want to check and possibly change the jetting based on the plug readings and et's. After all of this is set, then go to the pump discharge nozzle size and accelerator pump cam selection to get the best throttle response and et.
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