Mikuni Pumper - OK, I'm sold

I finally got to go out and ride for a day with my new pumper carb. It is better than my first impression. Here's the thread for that:


It was really easy to pull up wheelies over any obstacles, a lot quicker to respond to the throttle with the pumper. I had been trying to tune out some popping on decel and went with larger jetting 132.5/17.5. That proved to be too rich. It was loading up pretty bad on downhill sections and was really hard to start hot.

At lunch, I jetted back to 130/15 and it was much better. But it may still be just a tad rich. I may need to do some more fine tuning on the fuel screw.

With the 17.5 and the 15 pilot, I was still getting constant popping coming down hill off the throttle. I just can't seem to tune that out. My stock carb is about as perfect as I can get it, near instant throttle response, great mid and top end, and no popping coming down hill. Starting iwith the stocker is quite the drill though.

Anyway, I'm going to be keeping the pumper, I really like it and the super quick wheelies it pulls up. Mid and top end seem the same as the stock carb. But with a 2 kick cold starting of the Mikuni, it is definitely worth it.

The Mikuni Pumper was the best mod I ever made to my XR. Some minor popping on decel is perfectly normal and to be expected if you have an aftermarket exhaust on the bike. Your fuel screw should be about 2 and 1/2 turns out. Make sure you have the little phillips head screw with the spring on it (on the pumper actuator arm) turned all the way in until the spring is neatly compressed. I don't have my XR any longer so the details are a little sketchy, but I do have a few pics of the pumper setup if you need them.

Trailryder42 should be able to chime in with some details...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now