1984 15 yamaha 2 stroke OVERHEATED?

[new2obrepair]

I took my jon boat out to the river sat morning, put in, fired up fine, pisser working strong? And ran @ 1 mile downstream, motor lost power, sounded strange like a exhaust leak. SMOKED hard. Then I cut it off, could not find a problem, but it would not restart, also not locked up. Let the "smoke" out of my trolling motor getting back upstream to the landing. Died within sight. The 15 limped in the rest of the way. have not tried to dissasemble yet as I have no Manual yet. But I do all my own vehicle maintenance. I know I can fix this. Any suggestions on cause? Suggestions on what to look for. I'v read a hundred posts already and I am impressed with the professional support base! Thanks very much!<br /><br />ARCH

 

[jim dozier]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

First do a compression test and report the results back here.

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

Sorry I did not mention it, tested it saturday, 90 psi on top cylinder, 85 on bottom. tested several times on each cylinder, results were pretty much the same. bottom spark plug gap was practically closed! I opened it up to about .035 and tested at idle, still sounds like an exhaust leak. water clamp did not work as cups too large to fit between fins so I stopped testing there. Does that help?

 

[Solittle]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

When was the last time that you replaced the waterpump and t-stats?

 

[jim dozier]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

When you say it sounded strange like an exhaust leak, could you be more specific? Do you see evidence of exhaust coming from some place it shouldn't like a gasket. Was water still exiting the exhaust relief holes? Was it still pumping water out the pee stream? When it runs have you checked to see if its running on both cylinders? Unplug (ground the unused lead) one cylinder at a time to check. If one cylinder isn't running you need to check spark, then fuel, then mechanicals you find out why.<br /><br />From your original description it sounds like you overheated the engine for unknown reasons. The question is whether you fried the pistons or something less ominous as a result. The compression doesn't sound too bad though. <br /><br />Put the engine in a garbage can of water and do the test for the cylinder firing and check the water pump output.

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

I thought I'd said the water pump was working, good pee stream the entire time. It is possible one cylinder may not have been firing due to insufficient spark gap, but correcting the gap did not cure the trouble. I will try to run in water at first opportunity. As far as an exhaust leak, I had blue smoke coming out from under the engine cowling on the river, have not repeated that yet as I have no regular garbage can to test in. Off to the store...thanks again

 

[jim dozier]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

You may want to look in the spark plug hole of the cylinder with the bad plug. Look for any evidence of dents in the top of the piston. You may have broken a ring and the pieces may have danced around in the combustion chamber and bonked the plug gap and dented the piston. It is suspicious that the bottom cylinder with the lower compression was also the one with the bunged plug. I don't know why else a plug gap would close by itself. The blue smoke under the bonnet suggests a further look. Maybe you blew a gasket under the powerhead. You need to run it again to see whats going on.

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

Well, I did the tank test, water stream strong at idle and low rpm's, got weak at high rpm's. So I'll replace the pump and the stats. bottom plug was probably installed that way, no marks on ground lug, not beat up at all, and broken rings should cause lock up in fairly short order. I should pull it all apart, but I just ran it in my garage, without ear plugs, (and gas mask LOL), and the motor itself ran ok, no mechanical pings or grinds. I bought the motor, boat, and trailer from a friend last year, he tuned it before I got it, so I did not! MY BAD. ONE last item, the book I got from the library states the correct fuel oil mix is 100:1. I've been using 50:1. Could this be cause of poor idle? The plugs are definitly oil fouled but usable. I will be replacing them anyway, but is my mix too rich or not? Thanks for all the help guys.

 

[jim dozier]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

Stick with the 50:1. OMC backed off of an earlier recommendation of 100:1 because of rusting in the driveway. A properly running engine should not foul plugs excessively at 50:1.<br /><br />Maybe all you need is a good tune up. After you replace the water pump impeller (which you should do on any used outboard unless you have documentation of a recent change) pull off the carbs and do a thorogh carb cleaning/rebuild with solvent, compressed air, and new rebuild kit.

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

ok, all parts are installed, and next comes the "road/water test" Wish me luck!

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

water test failed - miserably. Ran ok, but pee stream was weak again despite new pump kit. and I could not run very far, I did however find that the smoke...and STEAM came out of the water outlet like a hot iron. So I am now sure I have a leak in the powerhead somewhere. Yes it did shutdown at temp as it should, and I did make a couple easily fixed mistakes in reassembly. gear shift synch and tiller handle alignment. But they both need to be redone again anyway at this point. Also noted oil leak when lower unit was upside down while re-installing it. Is that normal, or do I have a leaking oil seal. I did not see water in the oil when I drained it! Thanks again for your help guys.

 

[jim dozier]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

Does this engine have a thermostat? If yes, take it out and put it in a pot of water and heat it up and note the temp it opens with a cooking thermometer.

 

[new2obrepair]

Re: 1984 15 yamaha 2 stroke OVERHEATED?

I have removed the thermostat and pulled the power head off the motor,. I found small pebbles and sand in the t-stat intake and coils, and throughout the head journals. ordered gaskets and t-stat, fuel pump carb kit. will post results later next week.