'66 Johnson 80 stalls with prop on, not when off

[riktweed]

We were baffled that our outboard started, idled, and ran great with the earmuffs on, but when in the water it stalled as soon as it goes into gear. When we took it home, it again ran fine at various throttles FWD and REV until we put into a tank of water.

So I pulled the prop and with the prop off it will run fine even in the water. Seems like prop load is killing it. Would there be anything besides bad compression that could cause that?

No fuel problem (runs fine out of water no matter what gear or throttle)
No electrical problem (ditto)

Will do a compression check next, but any other advice would be appreciated greatly.
Thanks.

PS) There is an outlet port at the back of the shaft where water sputters out along with some steam. Should this be a steady flow of water or not? I am concerned my problem might have started with a cooling problem.

 

[jonesg]

Re: '66 Johnson 80 stalls with prop on, not when off

Its not running on all cyl's, so it either has a likely elec ignition problem or ... fuel supply with one carb.
They run fine on the hose with a dead cyl because theres no backpressure or prop load.
Use a spark tester set to a 7/16th inch gap to test spark, it must jump that wide gap to be good.
Adjustable spark testers are cheap at auto stores, $12 or less.

You may also need a water pump impeller, $12.
Test for overheating with your hand on the cykl head, it should just feel uncomfortable, not sizzling hot.
Or get a cheap infra red therm and shoot the temp.

 

[Silvertip]

Re: '66 Johnson 80 stalls with prop on, not when off

Running an engine on muffs vs in the water results in a difference in exhaust back pressure which is why all carburetor adjustments, especially idle RPM and idle mixture should be done in the water. So just dunking the motor may be enough to cause it to kill and the problem gets worse when you put it in gear. Yes - turning the prop takes power. Idle speed too low or mixtures wrong means the engine will die when put in gear.

 

[riktweed]

Re: '66 Johnson 80 stalls with prop on, not when off

Thanks so much for these pointers, sirs! We will begin examining more closely this weekend and I will update on progress. I am glad to hear there are possibilities other than "the motor is fried." We just bought it from a non-boater (on a nice little '66 MFG V-Hull), so I have no reliable history, unfortunately. We will check the spark, replace the impeller, and check compression. I will consult the manual about carb and timing adjustment, as well. All good advice, thanks again.

 

[jonesg]

Re: '66 Johnson 80 stalls with prop on, not when off

A timing light is handy to find a dead cyl if its spark related too.
You ought to go through it top to prop and check everything before running the snot out of it.
Change the gear oil, examine oil for water intrusion, replace drain plug seal too.
Peace of mind is priceless.

 

[riktweed]

Re: '66 Johnson 80 stalls with prop on, not when off

Pulled the plugs last night and found two were severely sooted and oily. Probably not sparking. The other two looked less oily, but also fairly blackened. Certainly looks like spark is one critical issue.

Someone has recently penciled compression readings on the heads, all are at or close to 123. Will need to do my own readings this weekend.

The plan is to rebuild carb and fuel pump, set points and advance (we have the basic distributor/coil ignition), and replace impeller. We will also drain the gear box and refill with new seals. Thanks again.

 

[riktweed]

Re: '66 Johnson 80 stalls with prop on, not when off

Part of our overhaul project involves replacing the impeller. Last night when we pulled the side access plate to disconnect the shift linkage, we discovered lots of stuff: small bolts, screws, rocks, leaves, paper wrappers, etc. When I stuck a needle nose in to pull on what I thought was a stick, what emerged was a large dead lizard. It would seem that the engine's upper exhaust outlet port has curb appeal for Florida critters.

I am looking forward to pulling the rear cover to see if we have an exhaust blockage due to nesting material. That might explain why one side is running well and one isn't. So far all the electrical systems are checking out fine.

 

[riktweed]

Re: '66 Johnson 80 stalls with prop on, not when off

Update - we pulled off the rear cover and found that all the critters and junk were only in the space between the exhaust chamber and the cover, so not impeding exhaust flow.

But we also discovered that the belt to the distributor is not installed properly and the distributor crankshaft alignment marks are off by close to 1/8 of a rotation, probably 4-6 teeth. That can't be good. So, the current plan is to set the belt correctly, gap the points, set the throttle/distributor advance linkage, new plugs, and give it a try again.