Motorcycle Repair: carburetor, cr250r dirt bike, air fuel ratio

Question
I just installed a new mikuni pre jetted carburetor on my rebuilt 1979 honda cr250r dirt bike. It will act like it wants to fire over but it will not, i have good spark to the plug. Help

Answer
Keith, there are three things needed to get an engine to run right...spark at the right timing, fuel in the right ratio, and good compression.  You've checked the spark and assuming it has the right timing, you're probably lookings at a problem with the air fuel ratio.  It could be too lean to start or too rich to burn.  Are the plugs wet with fuel after trying to start it?  If they are, it too rich.  If you put a little fuel on the air filter and it starts, it's running too lean and the choke or float levels need adjustment.

Regards
Rich