'05 CR250R ...... a motor at last

[jrm]

I'm running the standard jetting at about 500 feet above sea level; if I rode it more in the extreme heat right now, I'd probably have to lean it a bit. The motor is bone stock in all respects.

My jetting feels very crisp (in cooler weather) and the plug looks good. I had the same detonation issue you describe. As the previous post said, a 50/50 mix of VP C12 and 93 octane pump gas completely eliminated the detonation and made the throttle response a bit stronger. The motor really rips.

BTW, make sure you keep your exhaust valve cables adjusted properly. Mine was a bit loose after about 10 hours of riding time. If you get some slack in the cable (usually during the break-in period) you'll lose some top end pull.

 

[oldfrt613]

The loose cable problem seems to go away after about 2 adjustments. Mine has been tight since April. Ring life - Started really riding my '05 in April. I ride about 3 times a week. The ring needed replacing mid June. I probably ride harder than most. On my '01, about 3-4 rings a season and 1 piston. This one is shaping up to be about the same with mabe 1 more ring change a season. I have just broken in the new GP style piston. Not near the boost in the bottom end as the '01, but does provide inproved roll on as well as soften, by no means eliminate, the hit in the midrange. Power mid and up seems to be the same as stock style. A good choice in my book, as the big hit in the midrange can be a bit of a handful at times. Well, got ta go - we just got a dab of rain, the track is prepped and I got to let the loam monster out to play !!