Yamaha 150 RPM's

[Bill T.]

I know this has been discussed before but I need to ask anyway. I have a 1987 204c with a 1987 Yamaha 150 on it. Question: At wide open throttle I only get 4500 RPM's The engine runs and sounds great, just not the RPM's I think you are supposed to get. The speed at 4500 by the GPS is 30. Any and all help greatly appreciated.

Thanks in advance.

 

[Grog]

The RPM's should be at least in the 5XXX RPM range. What size/pitch prop do you have?

 

[Bill T.]

Not sure Grog, I will have to check it out later today and get back. Boat not here where I'm at right now. Thanks for the reply.

 

[BobP]

What's the existing prop size?

 

[Bill T.]

Grog and Bob P,
Thanks for the reply. Not sure what the prop size is actually. It is SS, not the polished kind. There are two numbers on it. One is "17M" and the other is "B 90184" I measured the Dia and it appears to be 14"

I took some pictures of it but do not know how to post them. If I have a e-mail address I do know how to send that way.

 

[wahoo33417]

That prop size sounds about right. Both Grady's and Yamaha's tests of the 205, 208 and 209 all had a 13 3/4 x 17 M prop with an F150. And with that limited of a top end I'm thinking that you would feel the boat struggling to get up on plane if prop size was the problem.

I'm wondering if there is a fuel flow restriction. Perhaps something as simple as throttle linkage adjustment or change of fuel filters?

That's about the extent of my knowledge, so I wish you luck!

Rob

 

[Bill T.]

Thanks Rob. The boat is now out of the water, the engine has been winterized by a Yamaha mechanic. I mentioned this to him and he said he would have to take it for a ride and check it out. (next year)
He is also a friend. STRANGE...... It didn't struggle to get up on plane, and sounded GREAT. Where did you get the info about the 150 Yamaha engine and the 205, 208, and 209 Grady's? Mine is the 204C, 1987. The engine is a 1987 150 Yamaha 2 stroke.

 

[BobP]

Maybe he has a 15.5 x 17 ??

Also, check to see if throttle plates are horizontal on motor when binnacle lever is full out.

 

[Bill T.]

Bob P.,
I measured the prop from the center of the shaft to the outer edge of one of the blades and read 7" As for the throttle plates, that will take a little time to check. The boat is somewhat closed up now for the season. BUT, thank you for the input. I may just have to wait until next season to finish checking this out. I'm sure it can be corrected.

 

[BobP]

Then the prop is not a 15.5 inch diameter but smaller as suggested and probably OK.

The dealer can check the engine out for you next season.

 

[Bill T.]

Bob,
It looks like I have about 1" above the blade edge before it would hit the engine. I have pictures of the prop, and could take more if you needed them but do not know how to post them here.

 

[Grog]

Since the boat's laid up and cozy until next year, before it goes back in I'd change the fuel pumps (if they haven't been done recently), they may not be able to keep up with the fuel demand at WOT.

 

[BobP]

Bill T , I wouldn't be able to offer any further advice. If you are a DIYer you could check the throttle opening yourself, costs nothing to do it.

It will be easy enough for a yamaha mechanic to figure out. Grog suggested the fuel pumps, I would tend to think the engine may surge with weak fuel pumps, or be intermitantt from one use to the next.

The Yamaha mechanic will also verify your tachometer is reading correctly and no fuel flow restrictions in teh boat, as well as the pumps working properly.

 

[Bill T.]

Thanks Bob and Grog,

I will check the throttle plates in the near future Bob. Other than that I guess the best bet would be wait until spring, and let Marty, the mechanic, check it out and come up with a solution.

Want to thank you both for your input, much appreciated.

 

[BobP]

Anytime, when you find out what has caused problem - report back - many will be interested.

 

[Bill T.]

Will do Bob. Be next spring or early summer.

Thanks ALL ........

 

[jekyl]

Bob...... you said that if it were the fuel pumps, then it might be an intermitent problem. As i have a similar intermitent problem can you explain please, why this could be so?
I assumed if there was a pump problem it would be constant.

 

[Grog]

If the fuel pumps are weak, you may not know it until you really open her up. If they're shot, the motor really falls on it's face.

 

[BobP]

Jekyl - intermittant problems are the worst to find if that's what you have. Need a good engine troubleshooter, most mechanics have little patience or interest in troubleshooting (IMHO) in the conventional sense today and prefer to shotgun it with wholsale parts replacements - as in - "you need it done anyway".

Surging can be intermittant, if you already tried Ande on SIM, I think I saw you over there, he's the guy, or you will have to find a local mechanic by you. Hence the importance of a good dealer support with motors these days, they are a lot more complex then before.

Good luck!

 

[JUST-IN-TIME]

best is use a portable tank with a vacuum gauge press gauge
i always have it in my car when i go fix a boat
has not failed me yet!!