Accelerator pump adjustment


New Member
May 9, 2005
I just installed a 4150 Holley double pumper on my 351 Windsor stroked to a 396. The engine is bogging down a bit when I step on the pedal, plus a crapload of black smoke comes out of the exhaust. I'm thinking its the acc. pump. Does anyone have any ideas or possible specs for a proper tune? Thanks!
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adjust the accelorator pump has an adjusment screw whih im sure you know of mess with that and do you have a fuel pressure regulator if so try turnning it down some and also try setting your float level these things will help the bogging and also adjust when your secondarys open.also what size carb is it?
holleys can be a pain so i say just fiddle with it at the track sooner or later youll figure it out if its making alot of black smoke you might have too big of a carb good luck :nice: also what size are the accel pumps if there 50cc pumps gat 2 30cc pumps and try them
Simply adjust the linkage so that there is no slop in it, you want the pump to begin to work as soon as you move the accelerator.
Your problem could be the accel pump cam, they are easily changed, (come in packs of like 5-6 different ones) this affects how much fuel is delivered how soon, and how long the overall shot lasts when the throtle is pressed. There are also two settings on each cam, a small screw labeled 1 or 2 on the linkage where the cam mounts also changes the cam profile. If its on 2, try backing it off to the 1 setting, if its still nasty, try a smaller/more gradual cam profile.
Also look up on their web site the starting reccomendations for discharge nozzel and power valve size. Either of these could also screw you up. Also if the PV is blown (caused by a backfire) it will also pour fuel into the motor.

note: powervalves are rated for the vacuum where they open. i.e- if it says 85 that means at 8.5" of vacuum the PV opens and gives extra fuel to the motor... if yours is set too high and you have a cam (lower idle vac than normal) it will open too soon.

Also check the float levels as long as youre there, they are often screwed up by people. The fuel level should be at the bottom of the sight glass. (buy the clear ones from moroso if you havent already, well worth 5-6 bucks in the long run.)

(imho) For street cars, the vacuum secondary H is a better choice. Easier to tune, more forgiving of size mismatch, etc...

Good luck,
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