I have an HRC kitted 2000 XR650R, converted to supermoto. Ever since installing the HRC kit, along with a full exhaust system, filter, air box mods etc. The bike has been backfiring on deceleration. . . a lot. I have checked the obvious things like exhaust and intake leaks, had it on a dyno to check the fuel mix (a lovely 13:1 to 15:1 all the way through the revs). But it still backfires. It's backfiring mainly at mid to high revs but only when i close the throttle completely, if i open the throttle a little it stops. Problem is, being a supermoto, i need the compression of deceleration to brake into corners. So i can't just raise the idle to get rid of it. I am now thinking that the problem is that it's running too lean when the throttle is closed (or there is a problem with the spark plugs, but i'll try that one last cause the HRC plugs cost a fortune here). So my question is (finally, sorry for the long babble), will increasing the pilot jet size richen my mix with the throttle fully closed and hopefully stop the backfiring? And, if it does richen the bottom of the rev range, will this kill the power at low revs and take off? I'm currently using a 68s pilot and a 185 main, and i have tried 3 jet sizes either side of the main with no success. Any help is greatly appreciated, i've just about run out of ideas to fix this. Tom.