Yamaha 90 Bogs

[catmandon't]

One of my 1998 Inshore 90's will start great, run fine under 1000rpm but then bog at about 1600 rpm. It used to eventually fire right up to normal cruise rpm's but will not do that now. The consensus was to clean the carbs and that is now done. That did not solve the problem. I think it is an intermitent wiring or oil flow problem but on the schematics I do not see a sensor that would do that other than the oil level sensor. Could a bad oil tank sensor limit the rpm's? Looking for any odd suggestions anyone has.
Thanks, I'm a new member but have learned a lot from reading the posts.

[boats.net]

The oil level sensor on engine oil tank will activate the low oil warning, if activated will reduce rpm's to 2000 rpms and buzzer will sound.

[catmandon't]

Thanks

This problem preceeded the yellow warning I am now getting after re and re on the oil tank. A previous repair had damaged the rubber cap on the sender and I am awaiting a new sensor. I do not get an alarm but did feel a little current leak from the wires. I hope that is the problem but I should get a buzzer if that is the case, correct. Is there any other sensors besides that and temperature that would limit the RPM? Remember it will magically run up to proper speeds at times.

[99yam40]

Does the alarm buzzer work?
You should be able to test by grounding the pink wire at the temperature switch or maybe even turning the key on (motor not running) with the emergency (man overboard) switch pulled on some motors.

You should be able to tell if it is in safe mode by checking the timing with a timing light as it retards the timing to limit the RPM

[catmandon't]

Buzzer

Good thinking. We had just realized that It does not have a buzzer on startup but don't know if it should. I will do those checks tomorrow. Is there a safe way to check oil flow being it is a mechanical pump and would have to be running to pump? I gather from posts that Yamaha only monitors if you have oil not if it is flowing.

[99yam40]

you are correct level only for the oil alarm
yes you would need to have the motor running on a pe mix while checking oil flow

See if this gives you some needed info,

[catmandon't]

Excellent

Thank you, that link totally explains the sensor. I'll re and re tomorrow and repost. I suspect the torn rubber on the sensor combined with some oil leaking out of the cap is giving some intermitent continuity to the safe mode circuit.
The previous rebuilders broke the link to the oil pump from the carb and we manufactured one today. Should the setting at idle be completely off or is there a starting point somewhat open? Sorry for all the questions but I am in Mexico and it is impossible to get parts or manuals. I am awaiting a response from Yamaha on PDF manual but will have one sent from boats.net with my parts.

[catmandon't]

Bad news, Good news

After fashioning a link for the oil pump linkage and disconnecting the oil tank sensor completely I ran it and got the same bogging under load. As I sat wondering what else could retard the timing I was staring at the linkage to the computer and had the revelation I should have noticed much sooner. Even though my throttle and shifter were working nicely, I had not noticed the secondary lever with the advance attached was not going with the throttle. I am working in the water so I came home to look at a blowup before taking it apart to see what is wrong. I am now totally sure this is the problem. I'll let you know.

[catmandon't]

Eureka

Well, did a re and re on the linkage and the secondary one was still hanging up. Checked all the parts and turns out the shaft running into the CDI was corroded and that was keeping the linkage from advancing. Seems so obvious when you finally find it.
The combination of dirty jets, bad oil sender and corroded CDI shaft made it hard to pinpoint. The MAGIC run up was when the linkage spring could finally move the sticky CDI shaft.
Good lessons, thanks for the suggestions.

[bluegoat]

I have a 1985 90 hp and had a similar problem. Get the boat up on plane around 3000 rpm and it would bog. Not every time though. I went through the fuel system at 1st thinking it was starving for fuel. Then I went through the oil tank sender and the thermo switch and replaced the thermostat.
Today I was out after pulling all the carbs off and going through them and it still would bog.
I got behind the oil level gauge in the cabin and disconnected all of the wires to it and the module that is attached to it.

Bingo it runs WOT all day long I hope this may help someone else.