1991 Yamaha 70HP won't go WOT

[keaton85]

Issue: About 80% of the time the motor will act like it's hitting a rev limiter and not go into WOT. Right after idle under load it will start acting up. Sometimes it will be fine and you can cruise around all you want at WOT without missing a beat. BUT throttle back down and there is a good chance it will stumble and hit a "rev limiter" a little past idle under load.

Replaced/Serviced:
- Fuel pump: Rebuild but there was very slight pitting to one of the seats on the metal flapper on the outlet side. Idono if this would cause an issue or not.
- Carbs: Cleaned 3 times, float level set to 14mm. Only issue was destroyed o-rings on the float needle seat. I removed them and tightened the seats back into the carb. I'm suspecting this should be fine?
- New plugs
- No air bubbles leading into the fuel pump (used a clear fuel line to check)
- sprayed carb cleaner around the carbs and around the stator, no air leaks found.

Other broken items:
- Lighting coils are shots
- RPM gauge works sometimes
- oil level on gauges doesn't seem right, as I'm at 1/3 tank and it states it's full on the gauges?

I really don't know what else to do now... if it was timing then wouldn't the motor have the WOT issue all the time and not just 80% of the time? How can I remove the temp sensor and the oil level sensor out of the system just in case those are causing issues? I really don't know how to rule things out here...

[99yam40]

If you find things bad replace them , do not just remove them and hope.

Give us the rpms not just "it will stumble and hit a "rev limiter" a little past idle under load."

Have you checked your alarm system to see if it sounds like it is suppose to?
Could be you have one coming in and limiting RPMs

Compression, spark, and timing are very easy to test, have you done that?
Need to check spark and timing will problems shows up. timing light should show both if you hook to individual plug wires.

Fuel pressure and vacuum is also easy to test to make sure the supply side is good and meets spec.

[keaton85]

I really wish I could see an RPM read out but the gauge doesn't want to work consistently.

Compression is 120,115,115 top to bottom....

I guess I will try and get timing set, test peak voltage output and see what I can come up with for resistance readings off the charge coil.

The buzzer alarm is not connected as it had been rewired without it. Is there a way to disconnect the oil level sensor and temp sensor to keep the CDI happy? just to find out if either of those are causing the issue..

[keaton85]

Overheating!

I'm going to replace the impeller and the thermostat tomorrow and then go from there. Hoping I don't have to pull the head as I probably won't get that off without breaking or stripping out a handful of head bolts...

So frustrating, but definitely learned something off this project.