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LopeMX

YZ426 Carb Adjustment?

3 posts in this topic

I mistakenly adjusted the "Pumper adjustment screw" on my 2000 426 Keihin FCR carb. The screw is located under the cable pulley on the right side of the carb and adjusts the amount of gas that is squirted everytime you twist the throttle. Yamaha recomends that you don't mess with the stock setting (MY MISTAKE). I can't find any reference in the Shop Manual on how to adjust this. Please, any suggestions?

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Hey, I think I already answered this question on DRN, no?

It’s too bad, there was a great thread on this here at TTalk but I think it is gone (dead link when I did a search). Here’s the URL if any admins want to check that, the thread’s title is James Dean – Accelerator Pump

I think the factory setting is one turn of delay at the set screw before pump operation. You may elect to remove your subframe and airbox and operate the throttle to see if the pump spray is hitting the slide. If it is you need to turn the screw in (more delay).

You may start with a setting that just misses hitting the slide and then increase the delay some more in small increments until you get the best throttle response. FWIW I ended up with an extra ¼ turn of delay on my YZ 426. ¼ turn in either direction will have a very noticeable effect on response.

Hope this helps!

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