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Old 12-28-2012, 05:51 PM   #1 (permalink)
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Crankcase detonation

Gents,
I have an '84 Excell III that just started "backfiring" through the carb. It was sounding like a puffing sound blowing back through the carb. I was running it and tuning it for my son to ride and it backfired. I saw flame blow into the vac line to the fuel pump.

What could cause the detonation in the crankcase?

I've never seen this before.

Thanks,
JM
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Old 12-28-2012, 07:48 PM   #2 (permalink)
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Hole in the piston crown, maybe? Could also be busted piston skirts...just guessing...
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Old 01-01-2013, 04:50 PM   #3 (permalink)
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Bump...

BTW compression is good, 120 per cylinder.

JM
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Old 01-01-2013, 06:35 PM   #4 (permalink)
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you could rule out a holed piston at this point. broken skirt still factors in as would reeds, stuck floats, along with a bad fuel pump.

could have been that the crankcase became saturated with fuel and ignited? plugged exhaust?
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