1987/1988 Yamaha 90hp timing adjust help!

[ollyjscott]

So I have recently bought what I thought was a 1990 model 90hp 2 stroke Yamaha but the more I look into it the more I think it's an earlier model. I would like to adjust my timing but the manual I found online is for the newer 90hp motors and mine looks like it has an earlier system for the timing retard/advance. Theattached images (if this works) shows the difference. My motor is like the one in the photo vs the one in the manual. Looks like my timing adjust arm is at the top of the throttle control lever. Does anyone have advice, instructions or a link to an online manual for this model of 90hp?

Help appreciated!

[robert graham]

Why do you want to make adjustments to the timing??....if you're having running issues with the motor then they could well be fuel system/delivery related and most probably not timing...unless someone has been screwing with it....

[rodbolt17]

cause its gotta be the timing, or a carb adjustment.
cause its got screws and knobs and such.
just cause its a FIXED mechanical thing that unless something breaks it never changes doesn't mean a thing.

if there is an adjustment someones gotta monkey with it.

I cant tell you how many EFI motors I fix that someones been playing with the IDLE adjustment screw .

[ollyjscott]

I wanted to know how to adjust the timing as the motor is running on 2 cylinders at low and mid rpm range. It's a 26 year old motor so chances are something could have loosened (the adjuster bolt for the magneto lever which alters timing). The service manual also includes timing checks as part of the maintenance schedule.

It seems the issue is a bad fuel pump diaphragm which is causing cyl #3 to run over rich, so a new pump is on order.

[robert graham]

I replace my fuel pump every 5 or 10 years if it's failed or not....if the old one's still working I toss it in the tool kit for a spare....

[99yam40]

I wanted to know how to adjust the timing as the motor is running on 2 cylinders at low and mid rpm range. It's a 26 year old motor so chances are something could have loosened (the adjuster bolt for the magneto lever which alters timing). The service manual also includes timing checks as part of the maintenance schedule.

It seems the issue is a bad fuel pump diaphragm which is causing cyl #3 to run over rich, so a new pump is on order.

Have you checked the timing with a timing light to see if it even needs adjusting?

Yes the leaking pump can cause #3 to run rich, and if it is an oil injection model it will wash the oil off of things on that cylinder and cause lack of lubrication problems also.
Hope you did not run it too long like that

A C90 with premix fuel does not run that risk though

[rodbolt17]

once set, you simply DO NOT ever need to monkey with ign timing unless something in the magneto control breaks.
its mechanical and works till it breaks.
go chase another bunny but leave ign timing alone.

[ollyjscott]

Thanks for the feedback here guys. I will trust in the advice and not worry too much about the timing right now. I'll check it with a timing light in the near future.

Agreed about the pump issue : I had imagined that too much fuel would dilute the oil injection in that cylinder. Compression on all 3 is still very good, I checked last night. I only ran it for around 2 hrs at 75% throttle while testing the boat and motor. Not sure how long the previous owner had it like that but I'm hoping it is something that happened during winter storage... Time will tell!

[rodbolt17]

what we are trying to say is NEVER randomly dink with ign timing.
in the past there were some static methods, they never worked.
the ONLY way to check idle,pickup and WOT timing is with a load and a timing light.
however once set its set for life UNLESS something breaks or someone gets their skinners on it.
that's also why Yamaha used a locking compound, it shows if anyone has dinked with the links.