2001 90hp 2 stroke starves for gas at full throttle

[RobSeal1]

Idles fine, runs full throttle about 30 seconds then tries to die and runs rough. I have changed the fuel pump, all fuel lines from the tank and the primer ball. When it starts to starve I can pump the ball and it takes off again. I am mystified. 11 years of trouble free use and this started out of the blue. Any ideas?

[robert graham]

Is your fuel tank vent open?....

[RobSeal1]

Robert, Yes, I assume so. Even so on my last test run I had the fill cap loosened.. Same issue

[99yam40]

you can monitor the fuel pressure and vacuum to see what is going on.

If vacuum is too high you know you have a restriction.
If this is a built in tank there could be a anti siphon valve or a screen on pick up tube causing problems.

Might be sucking air at a connection also

[RobSeal1]

Pulled pick up tube. Eliminated anti siphon valve, pick up tube is a beveled end, no screen. Cleaned carbs during the whole process. Test drove after each step. No luck.

[RobSeal1]

Put brand new connector at engine. Seems to be tight. While running new fuel line, double clamped at all connections.

[TownsendsFJR1300]

Did you check the filter and gasket inside the engine(parts 7 & 9?). If that gasket is not holding a seal it'll cause issues...

My fuel filter cup, due to ethonol, expanded and would seat fully causing a vacuum leak. A new cup, solved my problem..


2001 90TLRZ Yamaha Outboard FUEL 1 Diagram and Parts

[RobSeal1]

I will check that tomorrow. Probably an inexpensive fix. Thank you. I did pull and clean it. Seemed to sit ok. How did you determine yours was leaking?

[TownsendsFJR1300]

I will check that tomorrow. Probably an inexpensive fix. Thank you. I did pull and clean it. Seemed to sit ok. How did you determine yours was leaking?

Yours is a bit different set up than my F150. The F150 has a cup with a flat lip that sits inside the "holder".

Anyway, we were headed out one day, engine dies just off idle (maybe 1,000 RPM). I was still in a canal and tied up to a dock and pulled the cowl. Primed the bulb and saw fuel coming out of the cups edge. Loosened the securring ring and found the cup wouldn't go into the "holder", maybe .005" too large (WTF?).

Got it back together, still not fixed but running again. Drove the boat up to the Yamaha marina and got another cup under warranty (mine was very yellow, vs clear when new). Service manager said it was a common issue with ethonol..

Slipped the new cup into the holder, no fighting, pushing, slipped right in and obviously seated...

Besides checking the above, another member recently had a cracked fuel "T". Between age and ethonol (mines an 06) I'd be priming the system fully and looking real close at ALL connections, plastic, "T"s, etc.

As a side note, I had the innerds of the "marine" fuel line between the transom mounted fuel filter and engine filter literally fall apart and came out.

Luckily the engine filter caught the particles/pieces.

You may want to simply drain the carbs into a nice clean tuna fish cup(or something similar) and check for any debris in the float bowls that may be getting sucked up into the main jets. Prime and flush wouldn't hurt either to each carb.

Good luck...

[RobSeal1]

Thank you Scott. I will do all of the above!

[ausnoelm]

How did you clean the carbs?

[RobSeal1]

Pulled off, opened up and used a spray carb cleaner. Should I have done more?

[TownsendsFJR1300]

Pulled off, opened up and used a spray carb cleaner. Should I have done more?

Pulling the actual jets out are about mandatory.

Some of them have very small orifices with sideways (horizontal holes) that won't get cleaned if varnished up bad.

Until you can literally SEE SUNLIGHT thru each jet, it isn't clean.

A fuel stabilzer / additive (Seafoam, Gas Shok, etc) is about mandatory IMO. Unless you literally drain your carbs everytime your done with it, the crappy ethonol fuel will goo up the carbs. Using those additives keeps the gas fresh MUCH longer and you won't have to do any draining, etc..

NTW, short of spraying the jets with carb cleaner, I'll use Brake Cleaner on the carb body. IME, certain carb cleaners are VERY STRONG and could possible damage non metal/brass parts...


**If its running FULL THROTTLE for 30 seconds, I doubt your carbs are dirty but could still have debris inside a float bowl, floating about, getting stuck in the main jet as the engine sucks fuel upward.