I know this is a common problem and I have reviewed and applied recommendations from many other threads but I can't cure this bike. I purchased a used 2006 CR250 with low hours and I foul a few plugs every ride. With a new plug the bike has lots of power and does not bog. If I idle, coast downhill, or ride casually the engine loads up or fouls plugs, so I need to ride WOT and last month I broke my hand in the trees. Now I’m riding again and need to get this resolved.
This is what I have tried with no results:
Air/fuel: 2 turns
Average ambient temp: 70 F
Spark plug: BR8EG and BR9ES
With the bike warm, the fastest engine speed is with the A/F screw 1-3/4 turns out which tells me the pilot is correct. Carb has been completely disassembled and cleaned many times.
Lightly oiled. Ran bike in garage with no air cleaner once and it still fouled.
Right Crank Seal
Thought is could be a bad crank seal letting tranny oil past. Replaced crank seal but made no difference.
Finally built leak tester and checked engine. With all ports plugged and cylinder at BDC engine leaked about 3psi in 10mins. Soaped entire engine down about 3 times and could not see any bubbles forming.
I’m ready to sell this bike but I really like it. Can anyone see what I’ve missed?