Carter style carb accelerator pump question.

[Frank Negron]

Hi. This question relates to a 750 Street Demon in particular but I believe it's for all carbs based on Carters probably even all carbs in general. It's so basic I feel a little foolish asking it.

At what point does the pump nozzle squirt fuel when working correctly?

The accelerator pump rod is set to spec and moves the pump rod/plunger immediately with any movement of the throttle. However the nozzle doesn't deliver fuel right away. It takes a good 1/8" downward movement of the pump rod/plunger before any fuel is squirted.

I always took for granted that there should be no delay and that there is a direct correlation. Hit the gas pedal and the accelerator pump squirts fuel.Thanks

 

[rumblefish360]

That’s the way I set mine up. The way you think it should be. On my AFB, AVS & TQ’s the plunger has a specific height that should activate the gas coming out of the nozzle as close to instantly as possible.

Check pump arm height, plunger depth, and how the fuel gets into or under the plunger. On some OE carbs, there is a check ball in a jet (for a lack of better terms) that allows fuel in as the plunger travels up. Others relay on a spill effort.

This may be a rod adjustment. I’m not familiar with the new Demon carb.

 

[Murray]

Not sure about your carb specifically, but some of these carbs have a check valve in the pump itself or somewhere in the circuit. On these types of carbs I disable the check valve so it no longer causes a "lag" in the accelerator pump operation. This results in an instant, strong shot of gas.

 

[rustycowll69]

if it has a leather cup plunger, I used to stick a small flat bladed screwdriver between the leather cup and the coiled spring behind the cup, because the leather gets kind of "glued" to the spring in manufacturing. I also lube the outside of the leather cup with a drop of motor oil, before insertion. I think those things help to improve the seal of the piston in the bore of the accelerator pump.

 

[Frank Negron]

Thanks all. It does a a "needle: below the nozzle but no checkball.

So it should be a 1 to 1 relationship? As soon as the plunger lever moves it should squirt fuel?

I'd assume that plunger cup is some type of rubber but I'll take a look

 

[rumblefish360]

Leather for OE Carters, rubber for the aftermarket carbs.

Thanks all. It does a a "needle: below the nozzle but no checkball.

So it should be a 1 to 1 relationship? As soon as the plunger lever moves it should squirt fuel?

I'd assume that plunger cup is some type of rubber but I'll take a look

 

[RustyRatRod]

The carburetor has three holes in the pump arm where the linkage from the throttle plate attaches. For a performance pump shot, the linkage should be in the hole in the arm nearest the carburetor. From there, you simply fine tune what's left by bending the linkage accordingly. A little trial and error and you'll get it in no time.

 

[Frank Negron]

Thank you. I've set it tospec multiple times alternating between the middle and top hole.

.25" from the top of the body to the bottom of the "S"hook. No matter what the fuel doesn't squirt till there has been at least 1/8" or more downward movement of the plunger. So it appears that either

• the accelerator pump well is low on fuel
• the pump cup has an issue

I'll need to order some gaskets, cup and check valve and l and take it apart to be sure