'72 Johnson 85hp backfiring and runs a little rough

ADK_Boater

ADK_Boater

Petty Officer 1st Class
Joined
Jun 29, 2010
Messages
217
I have a '72 Johnson 85hp that is backfiring at start up and then periodically thereafter. It also runs a little rough. I set the points gap to spec,cleaned the points and cleaned my carbs. I have fresh gas mixed 50:1, and I'm just a little confused.
Does anybody know what makes an engine backfire ?

Thanks for any help.
 
S

schematic

Lieutenant Junior Grade
Joined
Jan 12, 2008
Messages
1,102
Re: '72 Johnson 85hp backfiring and runs a little rough

lean condition, timing issue, intake leak, carb synch out, carbon build up,
 
Watermann

Watermann

Starmada Splash of the Year 2014
Joined
Jan 12, 2013
Messages
13,753
Re: '72 Johnson 85hp backfiring and runs a little rough

A backfire is caused by the ignition of the fuel air mix either inside the exhaust or the air intake. I would not continue to run the motor until you resolve the issue, it will end up causing permanent damage. Start with checking the timing.
 
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