Yamaha 150 2 stroke RPM drop from 5900 to 4000

[yama8454]

I have a 2009 150 2 stroke that gradually loses RPM's from 5900 all the way to 4000. Once engine is at 4000, it holds that RPM quite steadily and for a lengthy period of time. More recently, I can no longer reach 5900 RPM's and WOT is maxed out at 5000 RPM's then gradually decreases to 4000 RPM's as before. There is no water in the fuel filter. I do have a 10 micron water seperator, that catches about 3 tablespoons of water in the filter. I only use non-ethanol gas, with double dose of blue stabil. this engine runs increadibly well between 500 and 4000 RPM's and does not misfire at all, nor does it smoke. It has very good pickup. When I stop the boat and press the primer bulb, that seems to help it get back to 5000 RPM's, but I cannot do this w/ WOT since I'm by myself.
I have 2 problems:
1). WOT s/d be at 5800 to 5900
2). Th RPM's s/d not drop to 4000.
What do you think?

[rodbolt17]

your biggest issue??
YOU ARE DRASTICALLY OVERSPEEDING THAT TWO STROKE.
MAXIMUM RPM on the two stroke is 5500 RPM.
other than that, go find your fuel restriction.
most likly a plugged filter element.
or not
blow it up if you wish.
niether 2 strokes nor 4 strokes tolerate lean running long.

[yama8454]

Thanking you very much for your very quick reply. This is a GREAT forum for replying so quickly and helping w my issue. The fuel filter is 100% clean and has no water or trash in it at all. The water seperator is only a few hours old. There are the only 2 filters on this motor...The water seperator (10 micron) and the fuel filter (under the cowl). It is a 2 stroke. Any other ideas? Also, why would engine run at 5900 if it's not designed to run that high? Shouldn't the governor be calibrated for 5500RPM, or is this an adjustment that should've been made to this outboard motor?

[99yam40]

You do not have the correct prop on the motor is my thoughts, that is why it is over reving.They do have rev limiters incorperated into them but you still have to prop them for your set up

You should prop it to hit the upper limits of the motors listed RPM range with the normal load you will be running.
All of this is part of normal set up of the boat and motor.

Rod is a Yamaha master tech, so listen to what he tells you, he knows his stuff.

You can use a fuel pressure/vacuum gauge to test the fuel supply system and take a good look at the fuel pumps.

[yama8454]

Thanking you for your help 99yam40. Very kind of you to give me incite. I will look into a prop swap. Are there any books on how to use a fuel pressure/vacuum gauge and test the fuel pump that you could recommend? if so, please provide the name and/or author. thanking you very much for your help w/ this matter...

[Sparkieboat]

99 is correct about Rodbolt..he does know his stuff...I think the Yamaha factory manual has the specs you want..check e-bay they are cheap enough..
every pitch up in prop size will reduce your RPMs approximately 200 RPMs...so pitch it so you top out at 5500 RPMs..do not over pitch so it goes under 5000 this is bad also. 5400-5500 would be best.

[rodbolt17]

can you post the FULL model number??
that would aide in identifying WHAT 150 HP yamaha we are disscussing.

[99yam40]

yes it is always a good idea to post your model # when asking questions so everyone knows not just you.

Here is another site that had a good explanation of testing fuel system that might help you.
HOW TO: Testing your boats fuel system.

[yama8454]

Again, many thanks for all of your comments and help. What a great forum! and what rapid response!
My model number is 2009 150 yamaha 2 stroke TXR.

[yama8454]

99yam40....What a fantastically great article you found!!! That was absolutely well written and easy to follow!! The article indicate problems caused by fuel restriction and/or fuel pump include, " Low WOT (Wide Open Throttle) rpms. (When the engine used to be fine)"
, which is exactly my problem, something you guys have indicated from the beginning. Thanking you very much 99yam40 for your help with this.

[yama8454]

Rodbolt17.. I did not know that the RPM's s/d never exceed 5500, and w/out a doubt, once I get this motor fixed, it never will EVER exceed 5500 RPM's ever again..Thank you for your incite and education on this. You probably saved me several thousands of dollars, and I truly appreciate your help with this, and such prompt help too!! Again..thank you Rodbolt and everyone else on this site for your educating me on this as well as many other things.

[rodbolt17]

the F150,four stroke motor, has an operatrating range of 5000 to 6000 RPM and we try to prop it with its normal load as close to 6000 as we can.
the 2 stroke 150 motors in 09 had a max operating RPM of 5500 and we typically shoot for about 5300 RPM with its normal load.
if it is carbed,dont trust you gave me the full model , and it will hit 5500 then I would suspect fuel delivery or a weak lift pump before stripping the carbs.
however the RPM drop is because its LEAN, run it lean long and a piston pops.

[yama8454]

This is a Yamaha 150TXR Outboard Motor Two Stroke. I will keep RPM's down to 5300 to be safe as you suggest. There was about 2 teaspoons of water in the water separator, but no water, that I could see in the fuel filter. Will verify fuel pump is good and check for leaks per doc provided by 99yam40.. Thanking you for your help rodbolt17!!

[yama8454]

99yam40... This was a great article on tracking fuel problems, and also easy to follow. Thanking you so much for your help with this... You wouldn't by any chance have an article, or a book I could get on removing the carbs and rebuilding/cleaning the carbs on this yamaha 150 2 stroke, now would you?
Thank you again for your help ....

[yama8454]

If any of you guys have any computer questions, I'm pretty knowledgable about computers in general...I would be more than happy to provide answers..yama8454