2002 Cr250r Big Bore Mods/jet Settings

[NOWWHAT007]

I had a fresh top end installed by Nicoll Racing in San Clemente. After two short track rides, the engine seized in the middle of my ride in Glamis and destroyed the piston and cylinder. I still don't know how that could have happended.

Since the engine was finally destroyed, I decided to do some long needed upgrades. So I had the motor ported & polished and put a 270 big bore kit on. Since the head was modified, I am told it will have to run on av race gas. I live in Southern California and do most of my riding in the desert or on the race track. Does anyone have any advice on jet settings? Any reliability issues on big bore kits?

 

[dirt bike dave]

FWIW, the big bore I had (KDX240) liked the stock jetting. Even though the engine needs more gas, it draws in more fuel and air with each stroke. That said, I'd go a little richer to start, just in case. Whoever built the engine should have a recommendation for you.

BTW, a cool day at sea level while riding in the sand would probably require richer jetting than any other condition. The bike is working much harder in the sand and generates way more heat, and the oxygen rich air requires more fuel as well. So many riders will richen their jetting when they go to the dunes.