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1991 6Hp Johnson running lean / Low compression?

S

Scotian

New member
I have a 1991 6hp Johnson (j6REIA) that is running lean.

I have reason to believe this motor has a bad upper crank seal, however it is not as clear to me at it has been in the past. The motor is running very lean, and requires the slow speed mixture to be turned out about 6 or so turns to keep any kid of an Idle. WOT is no problem, has decent throttle response. The reason I question the seal, is the ignition plate is not covered in oil as I have seen in the past, however there is oil residue there. I am confident the carb is clean, and there are no air leaks in fuel lines, intake gaskets etc.

The one thing this motor does not have going for it is compression. It will build about 75psi. Although I would be content with this in an older motor of the same size, I am unaware at what kind of compression these “newer” 6hps push. Could it be that the compression is too low, preventing the motor to idle without a super rich mixture?

I bought this motor knowing it had overheated, and intended to use it for parts, however the “it should run” in me has gotten the better of me.

So:

Are crank seals a common failure in these motors

Is the compression too low to idle

I realize this may have been a little long winded, and I do have some more questions about an 8hp as well, however I will save those for another post.
 
Crank seals rarely fail.------I would remove cylinder head since motor overheated.-----Inspect cylinder walls.----Cylinder head is now warped and needs to be refinished.
 
What state are you or the previous owner buying the gas? If you have ethanol, the upper crank seal is likely punky and soft. I have done many of these seals over the years on that VERY SAME MOTOR. The top of my workbench is littered with bad crank seals from ethanol destruction. I am here in MN where ethanol is mandated. Compression is low but would not produce those symptoms in my experience. But I've only been doing this work for 50 years, not near the experience of Joe and Racer, among many others here. So take my advice with a "grain of salt".
 
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Tested a similar / same motor.----Gauge stops rising at 110 PSI----1990 8 hp----Did you pull the flywheel off to inspect around the seal ?----Used oil around the seal and pulled the cord to look for bubbles ??-----Bad seal does not have any effect on compression in the cylinder.
 
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racerone said:
Tested a similar / same motor.----Gauge stops rising at 110 PSI----1990 8 hp----Did you pull the flywheel off to inspect around the seal ?----Used oil around the seal and pulled the cord to look for bubbles ??-----Bad seal does not have any effect on compression in the cylinder.
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I did pull flywheel. There was some oil residue, but not the amount that I’ve seen on motors that have had bad crank seals in the past.

I tested seal by squirting small amount of water and turning crank - no bubbles.

Perhaps compression may be playing a factor in its refusal to idle, where yours is at 110 and mine 75? How well used was your 8?

Even at 75, do you think it would atleast idle, and not fall off and stall like it does?

Althought i I do believe this is irrelevant, the seal on the charge coil has melted away. Replaced it with a working coil.
 
timguy said:
What state are you or the previous owner buying the gas? If you have ethanol, the upper crank seal is likely punky and soft. I have done many of these seals over the years on that VERY SAME MOTOR. The top of my workbench is littered with bad crank seals from ethanol destruction. I am here in MN where ethanol is mandated. Compression is low but would not produce those symptoms in my experience. But I've only been doing this work for 50 years, not near the experience of Joe and Racer, among many others here. So take my advice with a "grain of salt".
Click to expand...

I am on the east coast of Canada, the nearest refinery in New Brunswick does add ethanol to their gas. Although I run shell supreme in all my small motors (no ethanol), I’m sure previous owners have ran regular. Although I hate to throw parts at it, perhaps the 25 dollar seal may be worth popping on?
 
I have an 8, I am going to sell it. I will test compression tomorrow. It is a late 80's and burned less than 10 cans of gas in its entire lifetime. Mint motor. Should sell here in Duluth MN for no less than 1200 bucks. Longshaft. They like 'em for the little sailboats here in Lake Superior. All my used motors carry a one year warranty, they don't go out unless they are golden. Everyone gets a free quart of Amsoil Saber 2 stroke. I expect it to sell within 2 days in Craigslist.
 
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An update:

I never ended up putting in a new crank seal. I was able to increase compression to 90 psi by snuggling up head bolts. Motor seemed to start somewhat better, although not a huge difference. Upon further inspection, I found that the throttle arm (the arm which pivots, that the throttle cable and ignition plate hook to) had melted on its pivot, likely when the motor had overheated. This had thrown the motor out of time, and also allowed for some slop in the arm. I stole an arm from an 8hp I own, installed, timed, and tuned carb. Motor runs well now.
 
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