What is it?

[ewalden444]

73 Johnson 20hp. Starts up first pull, but backfires, and backfires, and backfires. as long as I give it gas it runs, but backfires every 4 sec.

Please help......Going fishing in 7 days.


Thanks Ed

502-777-6831

 

[weldbilt17]

Re: What is it?

I Have A 75 Model 25hp Evinrude That Done That Same Thing And I Adjusted The Linkage Going To The Carb From The Cam On The Flywheel And It Helped Alot, I Guess It Was'nt Geting The Right Amount Of Fuel For The Amount Of Timing That Was Present

 

[jbjennings]

Re: What is it?

Ed,
Is your armature plate moving freely when you twist the throttle? You may have a motor running on one cylinder and the other cylinder is getting intermittent spark. That would be my guess anyway.
I can tell you that if you keep letting it backfire, you may break a reed. Is it lean coughing and blowing back through the carb??? If so, your idle jet is too lean and you need to richen the mixture by turning the idle speed adjustment counterclockwise. That's also a possibility. Hopefully that's it because it can be adjusted and fixed in about 5 seconds. You need to determine if it's a backfire through the exhaust (BAD TIMING) or a lean cough/sneeze (dirty carb) through the carb. After thinking about how you described it, I believe it's probably a lean cough. Try the idle air adjustment and if it doesn't smooth out, try a carb. rebuild.
Hope this was helpful,
JBJ
JBJ

 

[ewalden444]

Re: What is it?

It's backfire through the exhaust

Ed,
Is your armature plate moving freely when you twist the throttle? You may have a motor running on one cylinder and the other cylinder is getting intermittent spark. That would be my guess anyway.
I can tell you that if you keep letting it backfire, you may break a reed. Is it lean coughing and blowing back through the carb??? If so, your idle jet is too lean and you need to richen the mixture by turning the idle speed adjustment counterclockwise. That's also a possibility. Hopefully that's it because it can be adjusted and fixed in about 5 seconds. You need to determine if it's a backfire through the exhaust (BAD TIMING) or a lean cough/sneeze (dirty carb) through the carb. After thinking about how you described it, I believe it's probably a lean cough. Try the idle air adjustment and if it doesn't smooth out, try a carb. rebuild.
Hope this was helpful,
JBJ
JBJ

 

[ewalden444]

Re: What is it?

I wanted to add it run great at high speed, No Backfire

 

[jbjennings]

Re: What is it?

I still think it's a dirty low speed circuit and a lean sneeze, especially since it runs great wide open. Take apart your carb and soak it, then blow out EVERY passage really good with high pressure air from an air compressor. I believe that will cure your problem. -could be wrong, of course!
JBJ

 

[tashasdaddy]

Re: What is it?

http://forums.iboats.com/showthread.php?t=244013