I have a 1998 polaris express 300, I have rebuilt the carb & put on new top end kit but still will not start, looks like the spark is blue the compression over 100 and the plug is wet with fuel, what could be causing it not to start now.

Thanks huffy3133

 

welcome! What is the actual compression reading? Over 100 can be 105,110,etc? If you have a new top end,compression should be in the 135 to 140 psi range if cylinder was bored and honed properly to a new oversize piston. Plus one other thing that a lot of people over look is crank seals when they do a top end. You have to have good bottom end compression along with a good top end compression for the fuel mixture to atomize properly and also to force this air/fuel charge back up through the transfer ports to the cylinder where it is ignited.
OPT

 

Thanks for your reply, I have 115 lb compression,new .5 over piston & rings cylinder honed and measured new gaskets and new carb kit, it will fire and backfire on starting fluid but will not start on mixed fuel. Before I did all this it would start and run as long as you rode but when you shut it off it might start back and then it might not.

Thanks again,
Ricky Huffine, Production Team Leader
Caraustar Industries
Franklin, Ky Team

 

115 is still low! You should have more than this if the piston is bored properly. Part of this lower compression reading could be because of leaking crank seals which affects overall compression reading. 115 psi is considered the minimum compression for this engine. OPT