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How Can You Easily Adjust the Accelerator Pump Of Your Vehicle?

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An accelerator pump is nothing more than a plunger that is designed to enhance the mixture temporarily 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. Yamaha Manual suggests that the key to successfully tune your accelerator pump is to get the interaction of the throttle, cam and rod in sync.

An important problem that you will have to resolve while dealing with your 40mm Mikuni Carburetor is to prevent backfiring out the carburetor through the breather. One thing you could do is to bring about a decrease in the level of the fuel injected when you are opening the throttle for the first time.

Pump of Your Vehicle


Duration Adjustment

You will first have to look for a duration adjustment screw. Right below the screw, you will find a lock nut as well as a bracket arm. The screw is threaded into them.

If you want to decrease the amount of fuel that is squirted, you will have to turn the adjustment screw clockwise. Similarly, reverse can be done by moving it anti-clockwise for increasing the content. To get the maximum amount of decrease, you will have to remove the screw and take the lock nut out.

  • Turn the adjustment screw fully clockwise.
  • Start the engine
  • Open your throttle
  • Any hesitation in the engine indicates that the fuel content is low so turn the carburetor anticlockwise.
  • Keep blipping the throttle and making an adjustment in the screw until all the coughing stops.
  • Turn the screw back in till the coughing stops again.
  • Tight the lock nut.

Time Adjustment Screw

This screw is present just above the duration adjustment screw. This is used to adjust the timing of the squirt.  By making changes in this screw, you could bring about changes as in delay or advance the onset of fuel squirt. The manuals can be a great aid in this.

In addition to this, you must keep in mind the pump timing. It needs to start spraying fuel before the throttle plate displaces. In any other case, it might pop back through the carb. It is important to turn the throttle slowly while looking at the throttle plate and make adjustments in the top screw out to make it come in sooner and in if you want to delay it. This will be very effective against maximum car popping and coughing.

If you have any problem with your pump plunger binding against the pump cam arm, make sure to push the pump plunger down when you open the throttle. It happens when the spring is too weak or if it is dirty. You must lube the sliding face of the pump cam arm and the plastic pump plunger cap with a dry slide graphite spray.

Thus, all the above information must be kept in mind. For more information, you could visit

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