How-To: FCR carburetor accelerator pump timing adjustment

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If you own a modern 4 stroke dirt bike, then it is equipped with a Keihin FCR carburetor. Most service manuals and even aftermarket companies have really complicated procedures for setting up the pump shot timing. I explain an easier way in the video above.


The Goal: Perfect Timing

I have found thatĀ if you adjust the timing screw until there is very little little play in the rod, then that is the perfect setting. This setting does 2 things: it allows the diaphragm to fully fill with fuel and allows the squirt to start as early as possible. You will want to double check the squirt either on your workbench or while it is installed on the bike (subframe/airbox removed).


Here is a link to the auxiliary fuel tank I used in this video. Super useful when bench testing carburetors.


Retarted Timing

If you turn the screw in, it will delay or retard the squirt, which is not good and it will most likely create a bog. You are basically adding more slack/play into the rod and it takes a good amount of throttle to take this play out and start the squirt.


Advanced Timing

If you back the screw out, you will advance or make the squirt come in earlier. If it is too far advanced, the squirt will usually hit the back of the slide, which is not desirable. Also, no play will be present in the rod and it will actually preload the rod, taking away usable pump shot volume.


Other Helpful Videos

If you have a bog when when whack the throttle hard, I would recommend that you check out my 4 stroke carb clean video first, then watch the 4 stroke jetting video to get rid of that bog and get that front wheel off the ground!



Have any comments or questions? Did the video help you out? Feel free to comment below.


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