Yamaha 80 Four Stroke Backfire

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Yamaha 80 Four Stroke Backfire

Postby mattro51 » Wed Oct 09, 2013 5:00 pm

Ok motor guys I need some help. I have a 80 Yamaha four stroke that has a condition of, what I assume is back firing, through the air intake. It does it at random intervals and throttle position does not matter. It has done this since I bought the boat. The motor also has a substantial shake when at idle, this smooth's out with an increase in RPM's. Other than these conditions the motor runs good. Good power, acceleration etc. I have changed the plugs and replaced 100% of the fuel lines, Is there anything else I can do or does this sound like a trip to the mechanic? Any input would be appreciated.
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Re: Yamaha 80 Four Stroke Backfire

Postby QuackerSmacker498 » Wed Oct 09, 2013 10:11 pm

Have you checked your compression? Shot in the dark, but possibly a slightly bent valve or spring out of whack in the valve train.....I've heard from a few people you are suppose to have valves adjusted on those Yamaha's. Don't know much about them other than they run great. Buddy of mine had Yamaha 150. Im pretty sure he had the valves adjusted at one of his service intervals.
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