[Nick5288]

I have a 2005 yamaha 25 2 stroke and Wile running the other day it just died almost like it ran outta gas. There was smoke/steam coming from the cowling and exhaust and had a metal smell to it. I let it cool and it started back up and will rev in neutral fine but when it is in gear will barely go almost just Boggs down. The motor is peeing strong and water pump was just replaced by previous owner. Idk if it is a lowerend issue or a overheating issue.. Anything will help the motor is in perfect shape and has never been neglected so I don't believe it is anything to do with that. Thanks

 

[Nick5288]

Just checked the lower unit oil and only about 1/2 a quart came out? Wasn't milky and no signs of it leaking...I'm thinking the previous owner changed the oil but didn't fill it correctly(possibly from trying to fill it from the top). What type of damage could I have caused if that is the problem? The motor will still start up perfectly but once in gear runs like crap.

 

[jmrodandgun]

Did you get any metal shavings or pieces when you drained the lower unit oil?

Have you tried taking the lower unit off with it in gear and turning it by hand? Dropping the lower unit takes like 5 minutes and you will know instantly if you have to pull the carrier. I suspect if the oil didn't come out full of metal then your problems is fuel delivery related. Leaky primer bulb, old fittings fittings, corrosion in the carb jets, could be anything.

Do yourself a favor and check compression. We had a small 2 smoke that got cooked from picking up an ice bag over the water inlet. It would start and run but die with any load. Pulled the exhaust cover off and the pistons were toast.

 

[Lowtidelowlife]

If it's bogging down and overheating it willggo into a warning mode and not allow you to go past a certain rpm. If you read back a couple threads my 25 stroke yamaha did the same thing. I thoughtIit was peeing fine butit wwasn't enough. Impeller and ther.ostat change are cheap and fairly easy. I know the previous owner did it. But that's what every previous owner says. Forgivesspelling on wworkphone

 

[Nick5288]

There wasn't any metal in the lower unit oil and it seemed clean. It seemed a little low but now thinking about it doesn't seem like that's the problem. It does seem like it was in some sort of warning mode because it would not go over a certain rpm. But there is no alarm or light going off. It is a 05 25mshd so I'm not sure if it just doesn't have a alarm or what.

 

[Nick5288]

It is a manual start with no battery to the motor so I'm not sure it even could have a buzzer or light on it

 

[cutrunner]

No buzzer, no light just rpm reduction during overheat.
that lower unit only holds half a quart or less of gear oil.
you may have sucked a bag like previously stated. Happens to me all the damn time, im like a magnet for bags

 

[Nick5288]

Ok so the top cyl is 120 and the bottom is 90 :-/ both plugs were fouled but the bottom looked like there was water in the cylinder..where do I go from here?? I'm guessing the motor overheated and blew the head gasket..

 

[cutrunner]

I would run an itense treatment of Yamaha ring free through the motor before i wrote it off as blown up. I would also dothe compression check on a warm just ran motor. Do those two things anr see wheee you are from there.
If you did overheat it that bad then you scorched the pistons and the cylinder walls, much worse than a $50 head gasket

 

[Salty_South]

My Dad's motor just did the exact same thing.  Random rpm reductions, steam, wet and super fowled bottom plug (also 25 2 stroke).  The issue with his motor was a blockage and corrosion to the head.  The corrosion was like a worm hole leading into the motor.  He replaced all the corroded parts, threw on some new gaskets, started it everyday and changed the spark plugs about 10-15 times and he is back up and running.  I can get more details if you like.

Good luck

 

[Nick5288]

Sounds just like what happened to mine except I pulled the top of the motor off and the bottom piston is toast..chipped around the edge and scored cylinder...so now I guess I'm going to bore .25 over and install new pistons and rings.(if anyone has any advice on doing this rebuild it would be greatly appreciated!)but there is a lot of corrosion build up around the cyl walls..if you could maybe try to find out what he replaced and what else there is to use to remove the corrosion. Thank you for all the help

 

[jmrodandgun]

Do you have any pictures?


I just pulled the power head on my Yamaha 25 to replace the swivel bracket, the power head was off and on my work bench in about 20 minutes. I couldn't imagine the labor at the machine shop being much to fit new pistons and rings. Find a reputable marine shop. Apparently automotive machine shops aren't set up for marine block boring/honing and do not have a clue what type of piston to cylinder wall clearance is required, what finish works, or how to chamfer the ports to keep from breaking rings.

 

[Salty_South]

Looks like he replaced head/cover/water jacket. A total of eight bolts. For corrosion protectant he used a good helping of 6-56 lubricant.

Hope this helps, good luck!