1968 20hp Johnson leaking unburnt fuel into water

[Kurt James]

I have a 1968 Johnson 20hp outboard (Model: FD-22M) with an odd fuel leak seen on the water surface. I can smell that it is unburnt fuel and it "rainbows" on the water surface. I thought it was potentially piston blow-by but I tested cylinder compression and both cylinders have great compression at around 110psi each. There are no leaks or smell of unburnt fuel under the engine cover. No fuel line leaks though out fuel system from tank to carburetor, no carburetor leaks & no leak from the oil tube (runs from lower piston to upper piston). It is only seen with engine running. There are no leaks with engine off when squeezing primer ball either. The engine also runs great with no performance issues. Lean to Rich fuel adjustment also makes no difference. Has anyone had this issue? Any suggestions for next steps in root cause?
Thanks, Kurt

 

[racerone]

This topic comes up time and again.------It is the nature of a 2 stroke engine like that.----See the confused owner of a 63 model SEA KING motor in recent postings.----I have said it many times.--- 2 strokes and the concept of oil mixed with the gas is not well understood !

 

[dingbat]

Perfectly normal..... why 2 strokes are banned in a number of jurisdictions

 

[Kurt James]

Perfectly normal..... why 2 strokes are banned in a number of jurisdictions

Thanks for your reply Racerone & Dingbat, but this is not a normal amount of unburned fuel. I've owned many outboards and this engine I have owned since the 70's and it has gotten worse over the past few years. Something has recently changed and that is why I'm looking for a potential fix. The smell of unburnt fuel is very strong and you don't want to troll with the wind. You'll get a headache fast! I was hoping for some ideas on what other issues could cause this amount of unburned fuel to get into the water. Video attached. Thanks

 

[dingbat]

The smell of unburnt fuel is very strong and you don't want to troll with the wind. You'll get a headache fast! I was hoping for some ideas on what other issues could cause this amount of unburned fuel to get into the water. Thanks

Same with my 200 HP.....that's why I troll up wind if possible.

Low compression
Sticky/failed thermostats
Dirty, leaking carb
Carb float(s) out of adjustment or sticking
Fuel mix over oiled

 

[racerone]

Thermostat stuck open ?----Ruptured diaphragm in fuel pump ??-------Easy to inspect and easy to replace with a factory diaphragm.

 

[Kurt James]

Thermostat stuck open ?----Ruptured diaphragm in fuel pump ??-------Easy to inspect and easy to replace with a factory diaphragm.

Thanks guys. I'll investigate those potential items.

 

[saltchuckmatt]

What kind of fuel tank? Portable or boat mounted? Fuel lines, bilge, does boat leak?

Cheap 2 stroke oil....mixing it correctly....I could go on and on and on.

Moral, if you can't fix it and it runs good.....run it or buy a new motor, possibly electric.