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10 Things you Need to know about Accelerator Pumps

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1.

An accelerator pump is nothing more than a plunger that is designed to temporarily richen the mixture until the engine can produce enough air flow to pull the fuel through the jets. Just like a bathroom plunger, a rod pushes on a rubber diaphragm, which plunges into a reservoir of fuel, forcing it into a small orifice which leads to the intake tract. When you turn the throttle on, a cam is activated by an adjuster screw to engage the cam that pushes on the rod. it sounds complicated, but just think of a toilet plunger. The key to successfully tuning your accelerator pump is to get the interaction of the throttle, cam and rod in sync.

2.

The best was to adjust the keihin FCR's accelerator pump is to start by disconnecting to. Say what? step on is to remove the cover on the right side of the keihin carburetor and wire the pimp linkage open. Then, correctly without giving the accelerator pump the opportunity to mask a poor fuel screw setting

3.

Step two is to tune the fuel screw circuit until the engine responds crisply and with out hesitation when rolling the throttle on. If its too rich (the fuel screw out too far or too large of a pilot jet), the bike will run rough at low throttle and black smoke will come out of the tail pipe. If its too lean, the engine will bog and begin to die.

4.

Step three is to determine if your carb's pilot jet is the right size. This is easily determined. The proper size pilot jet will allow the fuel screw to be adjusted between one and two turn out. If you go out farther than three turns or in more than one turn, change the pilot.

5.

Once you have the fuel screw adjusted, release the accelerator pump linkage, turn the throttle wide open and watch the linkage. If the spring-loaded lever begins to spread before the throttle opens, the diaphragm stopper is bottoming out too early. Diaphragms are available with different stopper heights in 1mm increments. Its best to use a diaphragm without a stopper if possible (link in Hondas).

6.

If you are unsure, modulate the pump linkage back and forth by hand. find the point at which the cam begins to engage the accelerator pump plunger, then use the adjustment screw to remove any excessive free play. This is your "zero" setting. Use a marker and draw a line through the screw, spring and bracket.

7.

Now that you have found a zero setting, you will be able to turn the linkage screw in to delay engagement (and vice-versa). MXA starts by turning the adjuster screw in one full turn from zero. We then make quarter turn adjustments to get the most fuel into the engine when it needs it most-at a larger throttle opening.

8.

The final step is to ride the bike. Ride it, feel how it performs, and make more quarter turn adjustments. it is worth making adjustments even after you think you have the adjuster screw perfectly adjusted...you learn as much by making the bike run poorly as you do from making it run great. If you go too far, you can always back up.

9.

The leak jet supplies fuel to the accelerator pump. Unlike a main jet, the smaller the number on a leak jet the bigger it is. There are two holes being bed by the diaphragm. The leak jet is a bypass directly back into the float bowl. most likely your bikes leak jet will be too lean from the factory as opposed to too rich.

10.

There are four popular accelerator pump products. The Boyesen Quickshot cover and R&D Power Bowl feature purging systems that remove air from the accelerator pump chamber; the

latter also offers external leak jet adjustment. Additionally, Ready Racing's Rapid Response Linkage and R&D's Power Spring eliminate or reduce the effect of the spring loaded linkage delay. Some tuners even go back to step one and wire the stock linkage open.

An old article a found out of Motocross action. Let me know what you guys think and how accurate you think this is?

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I like the Stealth accelerator pump cover. Good article. The '07 and later 450X carbs are much better where the AP is concerned IMO.

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1.

The leak jet supplies fuel to the accelerator pump. Unlike a main jet, the smaller the number on a leak jet the bigger it is. There are two holes being bed by the diaphragm. The leak jet is a bypass directly back into the float bowl. most likely your bikes leak jet will be too lean from the factory as opposed to too rich.

That does not sound right. The smaller the number, the smaller the jet. Plus it contradicts itself by saying it supplies fuel, but is also a bypass. I believe the latter is correct. It is a bypass, therefore the bigger the jet, the more fuel is bypassed back to the float. That is why bigger jet numbers result in less fuel.

If I'm wrong, I blame it on being late and I'm tired.👍

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I have to disagree on a lot of what was posted there.

Pilot circuit (fuel screw) is for idle and the effect dimishes as you open the throttle. It is all but gone by 1/8 throttle.

asShake saidm, the small the number the leak jet, the smaller the jet. Contrary to other parts of the carb, a smaller leak jet causes the AP to squirt more fuel and be more sensitive to throttle input.

Only way to correctly set the timing screw is by checking the squirt.

Fine tuning of it has to be done by riding and trial and error. This is only needed iof you are an absolute expert and have a case of OCD.

The Power bowl, Quickshot are not needed. At most, an adjustable leak jet on leak jet equipped carbs due to the ease of adjustments though many find once an appropriate leak jet size is determined, they never have to mess with a leak jet again.

I did a write up of the O-ring mod and most of the AP setup.

O-Ring Mod and AP Tuning

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