I have a 86 trailboss 250 will not start put new crank seals compression was at 120 and has good blue spark but if you put just a little gas in the spark plug hole it will not fire only a backfire every now and then thought timing was off checked key and stator has not been moved this machine was running then just died can the cdi box or either coil go bad and still have spark but set the timing off.