A few questions about a recent purchase of a Yamaha 15 hp 1991 motor

[Seahawkfan]

Bought the motor last week from a guy on CL last Friday. The motor (believe it or not) only has 10 hours on it and looks brand new. It was stored for 2 years after being fogged and starved for fuel. When I got the motor home I stuck it in my barrel and only had to pull on it 5 or 6 times before she started up roughly (hopefully due to the fogging effect) and then after the smoke subsided she ran really smooth and pissed like a horse.

I plan on replacing gear oil and rebuilding the water pump along with a new impeller (or do I even need to do that?). My second question is do you guys or gals think I need to rebuild the carb or can I run sun sea foam or something through it? The Carb from the outside looks fine. I don't want to pull it off unless I have to. My thought is to do the above mentioned work and take her out on a run to see how she goes but don't want to harm the motor.

Is there anything I'm not thinking about here that I should be? Thanks for your help in advance.

 

[Irishrover]

Welcome to the forum....If it had a good out flow of water I wouldn't bother with the water pump and impeller, just check the gear lub and see what shap it's in. If it's clean it should be ok. If the motor is running fine don't mess with the carb. Remember the old saying if it aint broke don't fix it. Running that motor and putting some gas through that carb might be just what it needs.

 

[eugene1]

I agree for the most part with Irish, just go and use it (I wouldn't mess with the carb). Although I would invest in a water impeller since it's been sitting for so long. Cheap insurance in case the rubber is brittle.

good luck,

 

[Seahawkfan]

I agree for the most part with Irish, just go and use it (I wouldn't mess with the carb). Although I would invest in a water impeller since it's been sitting for so long. Cheap insurance in case the rubber is brittle.

good luck,

Copy that! I bought a complete water pump kit so I will just change the gear oil , drop the lower unit and take a gander to see how everything looks. At the very least, I will replace the impellar.

Thanks for your input.

 

[mikeee2362]

At the very least, I will replace the impellar.

Good Idea!!!
Change it even if it looks perfect, after over a year of sitting it will lose its flexibility and take on a curved shape and not put out like a nice new flexible one.

 

[Seahawkfan]

Just got done dropping the lower end and installing new water pump gaskets and impeller. The old impeller look to be in perfect shape but I switched it out anyway. I'll just keep the old one in my emergency kit until next year just in case. The gear oil looked like new also but I changed it anyway.

Now for the much debated fuel mixture question. As, I'm sure most of you know the owner manual of this 1991 Yamaha 15 hp calls for 100 to 1 fuel mixture which in my mind seem way low no the oil part. Also Yamaha recommends 25 to 1 during the 10 hour break in period which is what this motor has on it as of now. When I first started her up my tank had a 50 to 1 gas to oil ratio since that's what I run in my 1985 6hp evinrude. I let her idle for a good 10 minutes before I shut her down on the first start in 2 years.

My thought is to run her on a 75 to 1 ratio when I take her out for the first time. 100 to 1 just doesn't seem wright to me.

Any advice on this would be much appreciated. Thanks again in advance.

 

[eugene1]

Good thinking!

I have a 89 and a 93 yamaha's. One has a direct oiler, but the other says 1:100. I run that at 1:75, no problems and not much smoke.

Best,

 

[Seahawkfan]

Well for what it's worth here she is. Thanks for all your guys input and thanks for the welcome to the forum.

Karl

 

[eugene1]

Mint!

That is a sweet looking 2stroke.

Mine are beat up pos's but they run great.

Best,

ps. welcome to the forum, we get lots of drive by's here, hope you stick around.

 

[mikeee2362]

Wow that's a clean one!! Good Luck with it!!

 

[Irishrover]

Nice. I can't really tell for sure but that prop almost look like a high thrust prop.

 

[Seahawkfan]

To be honest I wouldn't know the difference but the guy did mention "high thrust" in his add. Do you guys think 750.00 was a fair deal? Probably a bit much for my 12.5 sea king but the rating label says up to 15hp and 777 lbs. It only weighs 25 lbs more than my 6 hp evinrude so I don't think there will be a weight issue as I am 160lbs. Also thinking about moving my 48lb thrust mincota to a bow mount and building a battery box at the bow to help even out the weight.

I know a lot of people think that its to much power for a 12 footer but just because you have that power doesn't mean you have to use it all.

 

[DrTheopolis]

My friend has an old riveted 14' Sea King with a newer 15 Horse Merc, and it works great. Doesn't seem to be too much weight, and certainly isn't overpowered to the point of being deadly or anything. I'm sure you'll be fine. Nice to have enough speed to get to holes that aren't right next to a boat ramp.

 

[Seahawkfan]

Here is a pic of the prop. Is a high thrust prop good or bad? I'm confused as to the research I have done so far.

 

[Irishrover]

A high thrust prop is great for trolling. I have a high thrust prop on a 9.9 yamaha kicker motor. High thrust may not be the best for your main motor, you will have less speed and they are not as fuel efficiant. What they are good at is pushing with power.

 

[Seahawkfan]

So does this one look like high thrust? I don't think it is after doing a little more research. It is a 9 1/4 x 10 1/2 pitch. I'm pretty sure it is the stock propeller.

 

[Irishrover]

That second picture is better. If it's 10.5 it's stock.

 

[Seahawkfan]

Ya, I was a little worried when you mentioned high thrust so I did some research on the motor and turns out its not a high thrust model or prop.

Thanks for your input.