2000 90hp 2 stroke performance problem

[2000yama]

i have a 2000 yamaha C90TLRY 2 stroke that starts fine, idles fine and will run smooth without a problem when kept around 4000 to 4500 rpm but if you go full throttle and run about 5200 for about 10 seconds it will loose power suddenly and you have to back off to a little above idle for awhile and the motor runs slightly rough but almost smooth once you bring the rpm down and doesn't try to shut off. if you try to give any throttle at that point it won't make power or rpm and runs very rough. if you stay at low speed for a while it will straighten itself out and you can go again. i checked fuel at filter and bulb was still firm indicating no fuel problem so i think it's spark somehow.I have checked connections, plugs and nothing apparent there.

[robert graham]

May be a weak or failing fuel pump, a fuel venting issue(be sure vent is open), or an air leak into the fuel flow(like at a filter O-ring) or fuel quick disconnect( check that O-ring)....

[2000yama]

potential fuel problem

Thanks for the help, Here is a little bit more info to digest. I first thought fuel also, so i shut the engine off the moment the power dropped off and the see through filter was full and i unscrewed a float bowl drain and fuel was present although i didn't let it drain to see just how much was there.there were no fuel leaks present either. With the motor seeming that all cylinders were not performing and the motor shaking as though misfiring and not wanting to respond to throttle no matter how much was applied and it didn't try to shut off from too much air with not enough fuel when applying throttle, i thought that indicated fuel wasn't the problem and was leaning toward electrical. Do you think that is possible to be electrical?

[robert graham]

"It runs well at 4500RPM's and cuts out at 5200RPM's"would make me think of a fuel flow or fuel venting issue...is your fuel tank vent open and clear?...

[2000yama]

fuel

I will check the vent, I had the fuel guage sending unit replaced and they installed a new fuel line to the motor and I haven't had it out since they did it so that's a good thought. I assume the vent is on the top cover where the line attaches on the tank

[TownsendsFJR1300]

Your may be on the right track with draining the float bowls. Drain them fully BUT catch what comes out in say a small SUPER clean tuna fish can.

You may a small bit of debris floating about then getting stuck / sucked into a main jet, that's what your looking for. If using ethonol, check older hoses (under hood fuel filter as well) for any breakdown on the internals of the hose. Nasty stuff.

Also, in any case, try running Yamaha's "Ringfree".

Its an excellent product, not cheap but goes a long way.

I've had VERY good results using it with somewhat dirty carbs, FI, etc, W/O dismantling. I've personally used it in bad cases, 2-3x's the recommended amount with usually good results. It is recommended, at least in the newer owners manuals to be used regularly... I do run it regularly in every gas engine I own...

[2000yama]

potential fuel issue

I drained the bowls and all is clean(no water or debris) and my gas tank is in the hull type and the separate vent hose that is next to the fill hose at the cap and is clear. i ordered a new fuel pump and when replacing it i will look at the old one for condition issues. I assume these outboards have spark advance and do they operate by the throttle lever position so more advance when more fuel is applied or some other method through the computer based on rpm?

[TownsendsFJR1300]

I drained the bowls and all is clean(no water or debris) and my gas tank is in the hull type and the separate vent hose that is next to the fill hose at the cap and is clear. i ordered a new fuel pump and when replacing it i will look at the old one for condition issues. I assume these outboards have spark advance and do they operate by the throttle lever position so more advance when more fuel is applied or some other method through the computer based on rpm?

Their NOT like the old Evinrudes where the manual linkage advance raises the RPM's before the carbs kick in....

Advance should be ECU con*****ed. Some, (from what I've read here), the base timing can be checked / adjusted..

[99yam40]

Some motor change timing at starting and idling until motor warms up and again as you raise RPM.
so monitoring with a timing light while starting and warming up will show what is happening

[rodbolt17]

do you have the digital gauge package?
does the audible alarm actually work?