Hi, I have a 2000 400ex with a 426 bore, cams, the whole nine yards. Its my buddys old racing bike. Well just recently I changed my fuel. I dont know if this would cause over heating and cause the blue smoke when I ONLY let off the gas. Instead of running about 104 I just have been using 100. What causes this?

Travis

 

blue smoke on decelleration would indicate oil burning, make sure u do not have too much oil added,the 400ex is sensitve to overfilling. If that is not the problem it could be the valve seals,I had to replace mine,it is a comon proplem on the 400ex. I also have a 2000 ex with the 426 in. I had to replace and rehone the cyl because the machine shop didn't fit the piston right,I replaced with a namura piston and is right now no oil burning. I hope this helps.

 

Usually the rings or valve seals.. My buddies was doing it real bad.. i replaced the rings.. no more. Good luck.