Logo

J100TRLCS, sudden loss of power while cruising at 3000 rpm

thomcheek

New member
Cruising at 3000 rpm, I had a loss of power and the engine stopped as if overheated or out of fuel. (Fuel supply is not the culprit here as I had earlier replaced the mechanical fuel pump with an electric pump which was satisfactorily delivering fuel to the engine.)
Overheating seemed to be the indications as exhaust smoke emanated from the exhaust cover, a brief sizzling sound was heard and the water pump telltale indicator showed water being pumped thru the engine each time I turned the engine over trying to restart.
Long story short, towed to the landing, now into the manuals, and the 1st order of things was to check cylinder compression. all cylinders tested at 60 psi, which looks to be below accepted standards. So I removed the carbs and intake manifold to check the leaf valves. The valves appearance was clean, no apparent damage, all leafs fitting tight.(I have not disassembled the leaf valve assembly yet.)
With no obvious damage to the valves, I decided to do another compression test on the cylinders. The results were 25 psi on all cylinders, some what lower than the previous test before dis-assembly of the intake manifold.
The compression test are really what is confusing me, and so I have stopped and started looking for some agreement whether I should disassemble the engine as the manuals instruct (or) have I went to far in trying to overcome what may be a much simpler carburetion problem or maybe a blown gasket.
 
Last edited:
The intake manifold, gaskets, leaf valves, reed plates, none of this assembly has anything to do with compression. The engine is a 1980 100hp 2 stroke outboard... NOT... a 4 stroke engine.

The original low compression reading was due to the bad overheating encountered, burnt gaskets, possible warped sealing surfaces, etc which only gets worse as time goes on.

You should have been warned by a constant steady buzzing of a warning horn. If not, find out why.
 
I realize this is a 2 cycle engine I don't know where you got the implication that I thought it was a 4 stroke. Nevertheless thanks for the input,yes a warning horn should have sounded, but it didn't so right, gotta check it out and fix it. Your direction as to burned gaskets, warped sealing surfaces etc. is mainly the reason for my inquiry. So from what you're saying is, follow the manuals, get deeper into the engine and the problem will should avail itself in that exploration. However what confuses me is that since you say the intake manifold, reed plates,etc have nothing to do with compression, why so much difference between the 1st and second compression test and secondly why do are all cylinders read equal pressures in both test #1 & 2.
 
Thanks for reply. Ultimately I was hoping not to go into the engine, that maybe there could be another problem. But it seems that's not the case, So the general consensus is further exploration into the engine is necessary. Thanks again for your time, have a good day.
 
You're checking valves, the first thing a mechanic would do on a 4 stroke engine. No matter, there's a lot of work to be done... at least you know the condition of the reed plate assemblies. No, I didn't say anything about the manuals, but if you have one, that will be to your advantage.
 
Thanks again for the reply, it seems that you guys, that are much more informed then I am, agree that I should take the hard road and go into the engine. The purpose of my inquiry was to insure that I was on the correct path of exploration. I have 3 manuals on the engine, a Clymer Manual, a Johnson Evinrude manual (part # 506837), and a Johnson/ Evinrude DVD shop manual. So with this information in hand and the ability to consult with you guys on the forum, I'm feeling much more confident that I'm headed in the right direction and will be able to effect the repairs. Have a great day.
 
The reed valves have nothing to do with compression in the cylinder !!!---Remove cylinder heads or the 4 bypass covers to inspect pistons and rings.
 
If you burned the thing up somehow, scored cylinders and such, there is no logical way that the compression would be the same on all four cyls. Defies logic.
Then you say it went from 60 to 25...and indicate that you think this is just aa small drop. I think that is what I read....
Again all four even at 25.

You know what I would do? Get another compression tester. Before I did anything else.

Something is not right with the tests you have done so far.
 
Just did that and found upper starboard cylinder scored, looks as if water made it into the cylinder, possibly from overheating and cooking the gasket. Now I've got to get to the repair which in part also determine why my overheat horn never went off. Thanks for the reply. Have a great day
 
found upper starboard cylinder scored, looks as if water made it into the cylinder, possibly from overheating and cooking the gasket. Now I've got to get to the repair which in part also determine why my overheat horn never went off. My question is, can I repair the damaged cylinder only with an over sized piston and rings or should all the cylinders be reworked, there is no mention of
this in any of my manuals.
 
Back
Top