only half power at full throttle

[camaroguy]

I have a 1987 pro50. It tries to go full throttle for about 2 seconds and then throttles down. It will not go more than 1/2 speed. No problems starting or running up to that point. Spark is good, compression is 125 on all three cylinders. Throttle cables look good. Fuel filter looks clean. fuel lines from tank to engine are new.

Any ideas on what to look for next?

[99yam40]

timing is a good one to check to make sure it is advancing and staying in spec while problem shows up.
The timing light will also show if spark goes away if you move it to the different plug wires

Most problems are fuel related so if spark and timing are good I would be cleaning the carbs and checking fuel pump

[TownsendsFJR1300]

Most problems are fuel related so if spark and timing are good I would be cleaning the carbs and checking fuel pump

+1 ^^^.

Has the engine been sitting for any lenth of time with fuel NOT treated? Un-treated fuel goes bad in as quick as a month and will varnish CLOSED the idle and main jets.

Pull the carbs, get to those jets and PULL them. Visually make sure you can see thru them. DO NOT just shoot carb cleaner at them and say their clean.. If you have a enrichment pump, clean that as well (located as part of one carb).

You'l likely see varnish on the bottom of the float bowls as well.

Yamaha sells a product called "Ringfree". Its an excellent fuel system cleaner as well as top end cleaner. It is NOT a fuel stabilizer. "Gas Shok" works very well, yamaha also sells stabilizers as well.

Good luck and please post your results..

[camaroguy]

half power

Yes the boat has been sitting and has only been out twice last year and not for a couple years before that and the gas was not treated. I will take apart and clean the carb and jets like you suggested. Will post the results after I'm done. Thanks for the advice.

[99yam40]

remember to follow the service manuals link and sync procedure any time you put the carbs back on

[camaroguy]

half power

and where would I find the manual for syncing?

[99yam40]

YAMAHA MANUAL STORE

find the part # you need and then order or look on the web for other options

[camaroguy]

success

Tore all 3 carbs apart and cleaned. Took the boat out today and it runs like a charm. Thanks for the information. Carbs and jets didn't look bad at all in fact they looked pretty clean but cleaning out the jets musta worked. Had a great time on the lake. kids loved that the boat was FAST and they caught a few fish.

Now, how can I tell if the oil injection is working properly?

[99yam40]

there is a procedure in the service manual for testing/measuring oil flow.
I am sure you did find a manual already.

Or mark the tank to see level drop and calculate how much gas and oil was used.

Are you running premix right now?

If not and the motor has not locked up from running then the oil is probably doing its thing

[TownsendsFJR1300]

Glad to hear its fixed!

Now, unless you like "do overs", or draining your carbs all the time, get and use some fuel stabilizer.

Just running it dry will leave a little bit of fuel in the bowls and it will crap up again.

Yamaha makes some good stabilzer, "Gas Shok" works very well too. Yamaha's "Ringfree" works extremly well cleaning (not a stabilizer) the entire fuel system as well as the top end.

BTW, thanks for the update!