The FCR39 MX, newer version of the venerable FCR39 has a new accelerator pump (AP) design. Many folks find they have a bog after installing an FCR on their DRZ. One of the reasons is the duration of the fuel squirt from the AP. This is easily fixed with a simple O-ring. Another method is the "BK mod" which involves drilling a hole, tapping it, and using a screw to limit the AP arm. Not near as easy as installing an O-ring.

Another newer fix for this issue is the After Market replacement AP spring from Merge racing

Using an O-ring like a #78 O-Ring (7/16" O.D. X 1/4" I.D. X 3/32" thick)Cheaper ones from a home improvement store will work, but a better solution might be to get one (or 5) from your hydraulic hose and fitting shop or Auto supply place. O rings made for hot oil and lots of pressure tend to work better for this then those made for water pipes.

(1) If you still have it, remove the throttle wheel cover from your FCR (and throw it away :busted: )

(2) Work the O-Ring over the timing adjustment screw.

(3) Pull the O-Ring over the black AP cam.


(4) Re-install the carb, go ride :thumbsup:

Thanks to William1 for the pictures :thumbsup: