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81 750C misfiring under acceleration

Marlboro750

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Ontario,Canada
Hello, im wondering if anyone can help me source the issue on my bike
so randomly the bike would start backfiring under acceleration between 3-4000 RPM.
installed new iridium plugs and it was fixed no more backfiring or sputtering.
it never ran so good in its life!!

Than... day in a half later it started backfiring again
i got the carbs synced and the idle improved but issue still remained

removed carbs for further diag
found a small pinhole leak in the accelerator pump
replaced that and still the same

my question is why did it run amazing with new plugs than shortly after go back to running like garbage
the plugs weren't fouled either

i replaced the wires as well due to age and misfiring in the rain
but i never changed or tested the caps
 
It improving then getting worse points at ignition issue. The caps can do it as well as using resistor wire with resistor caps. Wire not screwed well into coil can do it. Weak coil can do it.

Ignition has the weird property of getting better even if you did not cure the major issue by changing something else to new, it then goes a bit running fine and then suddenly back to the missing. I've seen it 500 times.
 
I'd check around your wires for arcing. Probably need to do it at night. I forget there used to be a trick with simple-green or armor all or some other cleaner that "helped" show arcing.

Perhaps if you just move the wires around so they don't get close to each other will help. Good luck.
 
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