Originally Posted by Mark rsa2au
Let us know if you find a solution.
I have checked and changed everything except the fuel pump & filter (next on list), but I still cannot get the revs above 4200 with out it misfiring / backfiring. Somedays it will run to 4500rpm / 42mph and stay there on 3/4 throttle but stutter / mis etc on full throttle. Pulls like a steam train up to 4000rpm though, above this is where the challenge is!
Can you run it at night, in the dark? You would want to remove the engine cover for this but it's more loud than unsafe (unless someone tries to stick their fingers in the belt and pulleys. Look for arcing between the plug wires- I think I mentioned them before and I would bet they're not insulating the way they should. Cross-fire will cause exactly what you're describing.