WOT Throttle only 3200rpms

[floatshallow]

First posting on the forum- first Yamaha. I bought a flats boat several months ago with an '05 50hp 2stroke Model 50tlrd. It ran at 5200rpm up to a month ago at WOT. Now it wont go more than 3200rpms

Checked spark at all 3 cylinders with a spark tester at 3/8" gap at idle. Checked good.

Put Seafoam in tank (6 gallon plastic) & ran for a while at WOT & sprayed directly in carbs.

Changed plugs & thermostat & engine fuel filter. No help.

Squeezed primer bulb at idle & WOT per Seloc book to check fuel pump & boat fuel system to motor. No change.

Need help. Any more tests or ideas I can try.

Thanks ahead

[99yam40]

Check compression and spark on all cylinders, then check timing with a timing light. If all that is good the pull and clean the carbs.

Be careful, if it is running lean on one or more cylinders it will eat the pistons if you run it that way

[floatshallow]

I checked the compression: cylinder 1- 110psi , 2- 110psi , 3- 100psi

I checked spark at idle with spark tester at 3/8" gap & got spark at all cylindrs at idle. If I get it at idle can I assume I have it at WOT ?

I have never timed an outboard. Can you tell me how to time it ? I would assume you clamp on to #1 cylinder at idle for a value in the book on the flywheel, but do you also check it at WOT. If so, how do you do it safely?

Thanks for your help

[LakeLanierTom]

Check that all three carb butterflys are opening.

Need help. Any more tests or ideas I can try.

Thanks ahead

Remove your carb cover so you can see into the throats (venturis). Have a friend operate the throttle from neutral to wide open (engine NOT running) and observe inside to be certain all three carb throttle plates (butterflys) are opening fully and in unison. If not, find and fix the linkage problem on the outside of the carb.

You symptom also describes an electronic ignition problem common to a stator (alternator) breakdown. More common to not be able to exceed 2500 rpm, but perhaps your tachometer is off a little..?

Could also be a sheared off flywheel key which would show up quickly with a timing light check. Your timing will be WAYYY retarded. The engine rotating parts are further ahead than the ignition "thinks", but this usually prevents starting and causes a condition where it won't idle with the throttle handle in the neutral position.

[99yam40]

I checked the compression: cylinder 1- 110psi , 2- 110psi , 3- 100psi

I checked spark at idle with spark tester at 3/8" gap & got spark at all cylindrs at idle. If I get it at idle can I assume I have it at WOT ?

I have never timed an outboard. Can you tell me how to time it ? I would assume you clamp on to #1 cylinder at idle for a value in the book on the flywheel, but do you also check it at WOT. If so, how do you do it safely?

Thanks for your help

Have some one else drive the boat or man the timing light and run it in calm water while looking at timing mark with light. It will also help you see if you are loosing spark at the problem RPM by moving pick up to the different plug wires.

I have checked WOT timing before also by disconnecting the CDI linkage from the throttle and with the motor idling moved the wiper to the WOT position while watching the timing marks with the timing light.

You could have a leaking fuel pump diaphragm that is flooding the bottom cylinder enough to not let it fire properly.

But more than likely you need to pull and clean carbs

[floatshallow]

I won't be able to check the timing until Wed.. I looked up the specs.- Idle 6-8 ATDC at idle. 24-28 Full advance. I presume these #'s are marked on the wheel & a pointer fixed somewhere.

[I]"I have checked WOT timing before also by disconnecting the CDI linkage from the throttle and with the motor idling moved the wiper to the WOT position while watching the timing marks with the timing light." [/I]

I am not totally clear on this test. By moving the wiper on the CDI box to WOT, Wouldnt that rev the engine up with no load & over rev the engine?

Thanks again for the replies & for bearing with me . I have not timed before & the Seloc book does not tell you how to do it. They only tell you how to adjust it by adjusting the throttle linkage. Quote "These models are equipped with an electronic ignition advance mechanism in place of a mechanical ignition advance system. Adjustment of the throttle linkage sets the timing"

[99yam40]

No, it will not over rev as long as you disconnect the throttle linkage and just move the wiper on the CDI not the throttle linkage on the carbs. The RPM will increase a little
Hook the timing light to #1 spark plug wire and it helps to mark timing marks you are looking for with something to make them stand out better

[floatshallow]

No, it will not over rev as long as you disconnect the throttle linkage and just move the wiper on the CDI not the throttle linkage on the carbs. The RPM will increase a little
Hook the timing light to #1 spark plug wire and it helps to mark timing marks you are looking for with something to make them stand out better

Thanks again. I will post when I find more. I have formulated around 10 tests to narrow it down & hopefully fix it.

[floatshallow]

Up date: It's finally fixed!

99yam40 - Thanks for your guidance for timing & checking spark with timing light at WOT. Those checked out good. Now I know how to time an OB. After I completed those tests, I did a carb test that was recommended by a mechanic @ simyamaha.com which was quick & easy to isolate the carbs. I ran at WOT & sprayed carb cleaner in each carb. #1 & 2 bogged down indicating flooding. #3 sped the motor up to normal WOT , which indicated the starving carb got fuel from direct injection in the intake. I took the carb. apart & found a huge chunk of what appeared to be lacquered fuel in the main jet orfice. I cleaned that up, put it back together, & now she screams like she used to!

I also installed an external Racor water separator/filter for added insurance.

Thanks everyone for your inputs. This is a great site!!!