1981 Johnson 90 HP Sometimes Locking Up

[Woodnaut]

Have a friend who is having some problems. Here is the engine:

1981 Johnson
Model: J90TLCIM
Serial: J5493077

The engine had been running smooth and strong. Cruising at ~4,000 RPM. Engine then suddenly slowed down to idle and then died. Tried to crank engine but it was acting like it was seized. Was able to turn engine backwards by hand about 1/2 turn and it freed up. Engine then cranked and started. Was running rough and would make only 1,500 RPM. Died again and felt like it was seized.

Next morning still felt seized, but could turn backwards by hand 1/2 turn and it freed up. Started and ran OK at idle . After 1 minute died and again felt like it was seized up.

Same series of events on next day.

Possibly a broken reed valve rattling around causing some trouble? Any thoughts or suggestions on how to diagnose are appreciated. Thanks.

 

[F_R]

Re: 1981 Johnson 90 HP Sometimes Locking Up

Reed? Nah, wishful thinking. Whatever it is, don't be doing that over and over. It is a serious matter and you are doing more damage.

Check the oil in the lower unit. If that is ok, you are going to have to start taking stuff apart and inspecting. Impossible to tell from here what it is. Could be something came loose under the flywheel. or a siezed bearing, or a multitude of other things. You do have oil in it, right? And it isn't overheating, right?

 

[Woodnaut]

Re: 1981 Johnson 90 HP Sometimes Locking Up

The cooling water tell-tale was present and no audible alarms were noticed so that would indicate the water pump was OK. Fuel in the tank was mixed at 50:1. The lower unit, however, we haven't looked at yet.

 

[emdsapmgr]

Re: 1981 Johnson 90 HP Sometimes Locking Up

Sounds like an overheat lockup. I'd borrow an infrared heat gun and measure the head temps when running. They should be in the 145 to 155 range normally at idle, less when on plane. If the engine is not overheating, you may have a fuel restriction in one of the high speed jets in one of the carbs. If a cylinder is starved for fuel (and lube oil) it can lockup as you describe, even if the engine thinks it is not overheating.

 

[cdoliver]

Re: 1981 Johnson 90 HP Sometimes Locking Up

My money is on a broken ring catching an exhaust port. Check your compression. Then take the head off to see how much damage you have.

 

[Woodnaut]

Re: 1981 Johnson 90 HP Sometimes Locking Up

And the winner is F_R with:

... Check the oil in the lower unit. If that is ok...

Turns out it's not OK. Mostly all seawater and fragments in the lower unit.

 

[HybridMX6]

Re: 1981 Johnson 90 HP Sometimes Locking Up

Yikes!

 

[tx1961whaler]

Re: 1981 Johnson 90 HP Sometimes Locking Up

Does the flywheel turn freely without the lower end?
At least a used lower end is cheaper and easier to find than a whole new powerhead!