I get a popping noise when I back off the throttle.

Is this normal?

Sometimes its quite loud, almost like a backfire.



'00 WR400

Try turning your air screw out a quarter turn at a time untill it goes away.

there ain't no airscrew on this bike. it's fuel screw.

if you can't eliminate the popping by turning ot the airscrew(2 -1/2 - 3 turns}

increase the pilot jet size. your probably stock with a #45. considering your in england and its probably not much warmer than 45-55F and maybe 50-60% humidity and below 1000feet in elevation, goto a #50. as the temperature warms, does it do that in england?, go back to a #48 or if it gets real warm, 80-90F?, go back to stock. if the #50 does not pop at all in the cooler weather, try the #48. some popping is ok. you should also find that starting is easier and warms up faster.

I had the same problem with mine (98), I turned air/fuel screw 2.5 turns and went through spark plugs on a VERY regular basis. I suggest you go up in pilot jet with air/fuel scew 2 - 2.25

I have since gone 2 yz timing (DVP needle 48 pilot 2.25turns out) not a pop in sight.

Thanks people....

All I have to do now is work out which screw is which. :)

I too had the same problem with my new 2000 426. For reference, I turned the fuel screw (pilot screw) all the way in and noted it in my owners manual (1.25 turns). Then I turned it back to the original setting and turned it a quarter turn out at a time. Ultimatly the pops went away with another full turn (total 2.25 turns out). After searching high and low for a short sloted screwdriver that I could use to reach and turn the screw with, I've found that the best tool for the job is a small extended slotted bit. I marked one side of it with yellow acrylic hobby paint which works as a reference point. In addition you can put the bit in a small socket to get additional finger grip if needed. Works great!



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