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1991 Johnson 8HP smoking bad

W

Watsy

New member
Hi all,
New to the 2 stroke outboard motor scene and have a smokin new to me one that I'm trying to get running better.

First startup it ran ok (smoking) at half throttle and up but died at idle.

So far I have;
Checked compression both cold and warm (110psi both cylinders)
Checked and gapped plugs
Taken carb apart, cleaned up and blown out passages.
Floated the float in water to make sure it was ok.
Found one very small brass tube running into the bowl (via a rubber hose) that was plugged up so pushed a very very fine needle through it and a a bit of scale came out.

Put back together and it idles very good now but ramps up somewhat rough and man does she smoke. (50:1 new fuel mix)
I have the what I think is the slow speed needle turned out 2.5 turns (seems to want to die when turned in under 1.5)

Any thoughts why its getting so much fuel?

Thanks muchly!
 
I use 25:1 mix in my Evinrude 3hp. Yes the engine smoking quite a lot, when i need test it on the barrel, but when in boat, i have visible smoke only during cold start. The quality of the oil used with fuel greatly effect the smoking. The better quality oil, the less smoke. Someone can tell, if the smoking also could related fuel pump problems? Plugs can be still the end of their life, even the gap is right.
 
Evinrudemen said:
I use 25:1 mix in my Evinrude 3hp. Yes the engine smoking quite a lot, when i need test it on the barrel, but when in boat, i have visible smoke only during cold start. The quality of the oil used with fuel greatly effect the smoking. The better quality oil, the less smoke. Someone can tell, if the smoking also could related fuel pump problems? Plugs can be still the end of their life, even the gap is right.
Click to expand...

Good point. Not used to running them in a barrel so I'm seeing the smoke in a confined area so will be more noticeable.
Just read last night that the pump diaphragm may be leaking into crank case causing the rich mixture so will rebuild it.
I agree about oil quality as well.
Plugs are new and gapped correctly.
There is hope.
 
I believe there is an assumption that " smoke " indicates a problem with the motor.----Just the nature / concept of a 2 stroke engine.----They always run on clean oil and when looked after that 8 HP will outlast the owner.----Some oils will smoke less than others.----Yes inspect / replace fuel pump diaphragm.----About $6.00 for that item.
 
I believe there is an assumption that " smoke " indicates a problem with the motor.----Just the nature / concept of a 2 stroke engine.----They always run on clean oil and when looked after that 8 HP will outlast the owner.----Some oils will smoke less than others.----Yes inspect / replace fuel pump diaphragm.----About $4.54 for that item on this site.
 
racerone said:
I believe there is an assumption that " smoke " indicates a problem with the motor.----Just the nature / concept of a 2 stroke engine.----They always run on clean oil and when looked after that 8 HP will outlast the owner.----Some oils will smoke less than others.----Yes inspect / replace fuel pump diaphragm.----About $4.54 for that item on this site.
Click to expand...

Thanks Racerone
I understand they do smoke to an extent but by anyone's standards this is excessive.
Yep, going to check out the pump.
Thanks for the lead on the diaphragm
Getting close!
 
Last edited:
Thanks for bringing this thread to life, Boobie. Welcome, Watsy. Evinrudeman has brought up an important point. If tuning in a barrel, they will smoke more and run rich. Are you running in a barrel? If so.....remove the cowling and if there is not a good breeze, then set up a fan to introduce fresh air. What happens is as the spent exhaust, with less oxygen for combustion, is sucked back into the carburetor, it will run richer. Then that produces even richer exhaust which gets recirculated back into the carburetor and before you know it the motor is running so rich it will barely idle. Fresh air is critical. Barrels are not the best place to test a motor, but fresh air, from a fan, will help a ton.
 
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The thermostat is a often a cause of excessive smoke. Much less smoke if the motor actually warms up. Thermostats fail, often, and usually fail open. Even working properly, many motors are reluctant to come up to temp without a load.(Idling in a barrel or on ears.)
 
Another good point. Older motors had no thermostat.....ran poorly cold....and without adjusting both high and low speed, depending on load and water/air temp. They were not economical. An operating thermostat.....usually 145 degrees, is a must. Thanks, Doryman.
 
timguy said:
Thanks for bringing this thread to life, Boobie. Welcome, Watsy. Evinrudeman has brought up an important point. If tuning in a barrel, they will smoke more and run rich. Are you running in a barrel? If so.....remove the cowling and if there is not a good breeze, then set up a fan to introduce fresh air. What happens is as the spent exhaust, with less oxygen for combustion, is sucked back into the carburetor, it will run richer. Then that produces even richer exhaust which gets recirculated back into the carburetor and before you know it the motor is running so rich it will barely idle. Fresh air is critical. Barrels are not the best place to test a motor, but fresh air, from a fan, will help a ton.
Click to expand...

Thanks for the welcome timguy,
Great points. Input is well appreciated
Yep, I'm running in a barrel with no where for the smoke to go.
I believe I am getting places with this actually. The small pickup tube in the float bowl (with the small rubber tube attached) being plugged wouldn't let it idle when I first got it.
Previous owner probably ran it like that for long enough to load it right up and then put it away. (It had oil dripping out of exhaust after I ran it the first couple times and took it out of the barrel).
With a carb clean up and new kit as well as a new fuel pump kit its running real good and the longer I run it it seems to be clearing up.
A good run on the lake is in order if the ice ever disappears lol.
Thanks to all for the insight..
Cheers
 
doryman said:
The thermostat is a often a cause of excessive smoke. Much less smoke if the motor actually warms up. Thermostats fail, often, and usually fail open. Even working properly, many motors are reluctant to come up to temp without a load.(Idling in a barrel or on ears.)
Click to expand...

Totally agree now that I am reading more and getting some good pointers.
I let it run for about 20 minutes just above idle (in gear) and after it warmed up a bit it smoked less.
I took thermostat out and verified it works (opens in the 140-150 range).
Love tinkering with this stuff and seeing progress..
Thanks again.
 
Okay, good....keep us posted. Sir Vic, in UK is very experienced with this motor like yours....perhaps he can add some advice.
Yes still iced in up here in MN too. Snow again yesterday.
 
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