2004 Wr 450, just rebuilt bottom end new Hotrod crank set, all bearings and seals in cases, oil pumps and water pump, Wiseco piston and cyinder plating, timing chain.
Put it all back together it started right up.
Stated break-in run great for 40 miles then it suddenly started sputtering missing and back firing, tail pipe got so hot it melted back fender and side cover.
Got it home first thing I checked was the carburetor, all jetts were clear needle moved freely and made sure all orifices, vacuum lines were clear.
The needle and jetting was as it has been for the areas I've been riding for the last 6 years.
Next I checked for spark.
Got a new tail pipe off Craigslist.
Bike would still start fine and run as soon as I give it any throttle it would still sputter and mis, after a few minutes the tail pipe would get very hot back-fire and eventually die.
The motor would never get any hotter then normal.
It seemed to me unburned fuel was making it into the tail pipe as it got hotter it was igniting there.
Tried to check compression but couldn't get a accurate reading because the exhaust cam has a release until the motor actually starts, to make it kick easier.
Then did a valve job [ was do anyways ] 5 new steel Kibblewhite valves and springs and resurface seats, thinking a exhaust valve was holding up.
Still had same issues.
When I first did the bottom end and had motor apart I did notice that one coil on the stator was burnt and cap was lose and a slight line was worn into the magnetic hub that spins around it.
Also that the battery I just replaced was failing so I would have to kick start some times instead of electric start.
My question is could the problem be the brunt coil on the stator and could the 1/32 line worn into the magnetic hub be un issue.
Any thoughts or ideas would be very helpful