85 HP Johnson Randomly Backfiring Through Exhaustt

[emdsapmgr]

The plastic ring under the timer base should be lubed with a white lithium grease. It's pretty slippery, even down to cold temps. Don't use a heavy wheel bearing type grease. After the engine has run for a while, I'd check the cyl head temps with a laser temp gun. The heads should idle around 143-150 degrees. If one is running significantly lower temps, you may have a thermostat that is stuck open. A cold-running head will not have clean combustion equal to the warmer head. Plugs can accumulate carbon and appear darker.

 

[jiju1943]

The plastic ring under the timer base should be lubed with a white lithium grease. It's pretty slippery, even down to cold temps. Don't use a heavy wheel bearing type grease. After the engine has run for a while, I'd check the cyl head temps with a laser temp gun. The heads should idle around 143-150 degrees. If one is running significantly lower temps, you may have a thermostat that is stuck open. A cold-running head will not have clean combustion equal to the warmer head. Plugs can accumulate carbon and appear darker.

Thank you so much, that really does make sense, I will replace the thermostat. The left head was no hotter than a piece of wood laying in the sunshine and the right head was not even warm to the touch. I will also pick up some of the white grease today. I don't have access to a laser temp gun. I will let you know how it goes. Thank you so much, I really do appreciate your information.

 

[Randy1977]

I have a 1985 30 horse electric choke baught it with a slight miss and a exhaust pop ,found a bad power pack and fixed both cylinders now they both fire with checked fly wheel for bearing play and was not exsesive also checked curosion witch I cleaned up compresion is 120 per cylinder and now that I fixed the other cylinder it sneezes harder and some times on the first crank it fires right up every time and to keep it from sneezing I put the auto choke to full open and the sneezing goes away when it’s running rich any sudgestion

 

[GA_Boater]

I have a 1985 30 horse electric choke baught it with a slight miss and a exhaust pop ,found a bad power pack and fixed both cylinders now they both fire with checked fly wheel for bearing play and was not exsesive also checked curosion witch I cleaned up compresion is 120 per cylinder and now that I fixed the other cylinder it sneezes harder and some times on the first crank it fires right up every time and to keep it from sneezing I put the auto choke to full open and the sneezing goes away when it’s running rich any sudgestion

Suggest you start a new thread. This one is old and inactive. Very few of our members look at old threads.

BTW - It's called a lean sneeze and using the choke richens the fuel mix. The carb(s) need rebuilt and adjusted.

Closed.