79' 85HP Johnson starting and running prob.

[fuquamx]

My outboard starts and runs fine in the driveway w/ the muffs on, but as soon as I put it in the water, it's much more difficult to start. Once I get it started, it will run fine in idle, but as soon as I try to put it in gear it dies. Help!

 

[jtexas]

Re: 79' 85HP Johnson starting and running prob.

welcome to iboats.

fuel line holding pressure? tank vent clear?

in the driveway your motor will idle fine on 3 cylinders but the water puts backpressure on the exhaust.

first, compression test.

second, cylinder drop test - engine idling, pull then replace the spark plug wires one at a time (use an insulated or plastic tool to avoid shock). if RPM's don't drop noticeably, that cylinder's not making power.

then check for spark, remove spark plug, reattach it to the boot, hold it against the engine block and look for a spark while somebody turns the engine over.

no compression gauge? skip that step.

all cylinders pass the drop test? get a spark tester (couple bucks at autozone), set it for 7/16", look for a sharp blue spark.

good spark all around? rebuild carburetors.

 

[wavrider]

Re: 79' 85HP Johnson starting and running prob.

All the advice above is great
I disagree with skipping the compression test. A 29 year old engine could very well be compression. If at all possible do the compression test, this will let you know if you have a weak cylinder as far as power.

All cylinders shoul;d be around a 100 lbs with no more than 10% variance.
Do not worry if it is less than 100 lbs but the variance is what you are looking for.

spark tester at the auto store are around $9.00, and worth the money spent in trying to diagnose ignition problems. You can make your own spark tester out of a piece of wood and a few nails and wire.

Let us know what you find out on the spark.

I have to do the same thing with my 73 85hp, just noticed today on the lake I had an intermitent miss at idle.

 

[ezeke]

Re: 79' 85HP Johnson starting and running prob.

And the spark and compression tests should be done with all of spark plug removed.

 

[fuquamx]

Re: 79' 85HP Johnson starting and running prob.

O.K. guys, I appreciate the advice given. Did the compression test and found that the top right hand cylinder was only producing 60lbs of commpression while the other three are at 120lbs. Obviously need to pull the head and check the piston and rings. My question....I very familiar w/ working on two stoke dirt bikes and am thinking pulling the head and replacing the piston and rings shoud be about the same as a dirt bike....am I correct or is there other issues on a outboard motor I should be concerned about? I figure I need to replace the head gasket, piston, rings, wrist pin, etc. Thanks for the previous help.

 

[ezeke]

Re: 79' 85HP Johnson starting and running prob.

The engine would have to be removed, torn down and rebuilt. Don't go there until you take the cylinder head off and see what has happened; you could just have blown a head gasket.

 

[fuquamx]

Re: 79' 85HP Johnson starting and running prob.

The engine would have to be removed, torn down and rebuilt. Don't go there until you take the cylinder head off and see what has happened; you could just have blown a head gasket.

Is it not practicle to replace just one piston in an outboard? I realize I could have a difference in compression with a brand new piston and rings, but the other three were at 120lbs and from what I can gather that's good compression.

 

[iwombat]

Re: 79' 85HP Johnson starting and running prob.

Yes, you can replace just one piston. But, to do that . . .

"The engine would have to be removed, torn down and rebuilt."

 

[jtexas]

Re: 79' 85HP Johnson starting and running prob.

note to self: never skip the compression test