Back firing after running fine???

C

Cajun Blues

Cadet
Joined
Jul 6, 2010
Messages
13
1996 90 HP Running fine for 20 mins on muffs. Replace faulty kill switch and a key switch that had an ant nest in it and now all it does is backfire. Good spark,nothing else has changed. I'm going out of my mind!!! I just want to fix this P.O.S. and get it out of my yard.
Any suggestions. Could the ants shorted out the powerpack or anything else?
 
W

wilde1j

Vice Admiral
Joined
Apr 15, 2002
Messages
5,964
Re: Back firing after running fine???

Have you had the flywheel off in the past year? A sheared flywheel key will cause that. Backfire is usually a sign a timing being way off. If the key is sheared, you have a few tries at replacing it right, before the flywheel and the crankshaft get destroyed. The flywheel must go on dry with the tapers clean and the nut must be torqued to the correct value.
 
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Dhadley

Supreme Mariner
Joined
Feb 4, 2001
Messages
16,978
Re: Back firing after running fine???

Which 1996 90 hp do you have? Crossflow or looper, the model number will tell. That info will help us lead you in the right direction.
 
HighTrim

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: Back firing after running fine???

Backfiring out of the exhaust port is caused by having the ignition system fire a particular cylinder when the exhaust port is open, sounding like a shotgun of sorts.

This is usually due to a sheared flywheel key as stated, a flywheel with melted (moved) center sensor magnets if they exist, timer base leads routed incorrectly to the powerpack, or having the leads from the powerpack to the coils reversed to mention a few.
 
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