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post #1 of 4 (permalink) Old 12-28-2012, 05:51 PM Thread Starter
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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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post #2 of 4 (permalink) Old 12-28-2012, 07:48 PM
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Hole in the piston crown, maybe? Could also be busted piston skirts...just guessing...

2007 Dragon RMK 700 155", 2008 RMK 600 155", 95 Prowler 550 2-up, Really OLD AC Cheetah

http://www.avalanche.org/accidents.php
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post #3 of 4 (permalink) Old 01-01-2013, 04:50 PM Thread Starter
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Bump...

BTW compression is good, 120 per cylinder.

JM
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post #4 of 4 (permalink) Old 01-01-2013, 06:35 PM
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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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