1998 C90 new powerhead tuning

[boscoe99]

What does any of that have to do with this thread? No reason to post stuff like that. Im trying to solve a problem and thought I could get some help on this forum. Its a very odd problem, I get that. Im not expecting answers imediately either.

This was intended for yam99. Not you. If not applicable to you, and you are not interested, don't read, and turn the page.

You are getting lots of help. For free. How much of a better price do you want?

I give lots of my time trying to help here. For free. I need a bit of levity from time to time.

Call Yamaha customer support. Good luck getting a man on the line that knows what a C90 is.

[flounder daddy]

hay lucy.
I spalined it once.
the C90 does NOT use any method of warm up detect.
the CDI at start up simply uses a time constant circuit to advance ign timing for a set period at each start cycle.

some 3 cyl Yamaha models do use a separate thermosensor to give feed back to the ECU. the c90 is not one of them.

yes there is an 800 # for Yamaha.

you are chatting with at least one Yamaha certified master technician.

biggest issue, your a raceum car bubba.

forget anything you thought you knew about them thar raceium cars.

it does not apply to high performance 2 strokes.

fix your fuel system.
go fish.

go to any ford,chebby, or Honda dealer.
tell the lead tech your vehicle runs well but after 15 minutes at 5000 RPM it falls out.
watch that techs peepers glaze over,
they never see any auto engine run much longer than 13 seconds at that RPM.
us boat moto mokanicks see 5500-6000 RPM runs that last hours.
longest I ever ran my F150 at 5700 RPM was about 45 minutes.
longest I ever ran my 455 olds above 5000 was about 13 seconds.

Thank you for the insults, sorry you dont know the difference between bubba gump living in his trailer "mechanic" and an actual precision toolmaker. Your preaching its a fuel issue. Im sitting on the boat, at the dock as im typing this. The engine took 12 minutes to idle down, and guess what!?! The timing fell back to 7* atdc and is idling at 875-900 and the timing is advancing as it should when given throttle. Does not sound fuel system related to me.

[99yam40]

OK , so it is changing timing and RPM as it should.
It just takes a little longer than you want.

It would be interesting to see if a different CDI would shorten that, but that is a lot of money to see if it would make the difference.

If the warm up period is a time constant type of thing in CDI, I am thinking turning it off and back on would extend the time.

If it was a temp thing then the heat soak idea would come into play.

I may be wrong, just a thought

[boscoe99]

OK , so it is changing timing and RPM as it should.
It just takes a little longer than you want.

It would be interesting to see if a different CDI would shorten that, but that is a lot of money to see if it would make the difference.

If the warm up period is a time constant type of thing in CDI, I am thinking turning it off and back on would extend the time.

If it was a temp thing then the heat soak idea would come into play.

I may be wrong, just a thought

Yep. Turn the motor off when hot. Then restart. If the time constant delay before idle down is faulty it should idle fast again for the same period of time that it is running fast when first started cold.

I learned something today. Did not know that some Yams used a time constant fast idle for a period of time. There is so much to know.

This post is for 99yam in particular and not for flounder daddy since it is not helping him solve his problem. Any others that want to read it, do so with my pleasure. For flounder daddy, move on, nothing to read here.

[99yam40]

Even My c40 when already warmed up will start at the high idle for a shorter period of time, but it is for just a few seconds not minutes before it idles back down to normal idle.
With nothing to tell it the motor is already warmed up, I do not know how that C90 reacts

[flounder daddy]

Im starting to think the CDI has a issue in cold weather. Im good friends with the original owner of this engine and even he stated that in the winter time it took a long time to idle down and act normal. I might just have to live with it. The last thing im going to put on is a new thermoswitch. It does idle a tiny bit higher when its hot and you start if after making a drift in the water, but almost immediately idles down normally. Whatever this mystery is, its heat/temp related.

[robert graham]

My 1999 C90 doesn't idle high when cold so I usually use the neutral throttle lever to run it at about 1200RPM's for about 30 seconds then she's ready to go...I'll admit to being very interested and curious about your long cold start issues....has to be something going on here, so keep us posted!