Yamaha 90 2 stroke idle. I’m at wits ends.

[Jonb1032]

Boat sat for a few months but was religiously started every week and idled for 5 minutes. Took out for a test quick run, when I returned to dock I noticed engine won’t idle. It drops rpm’s and dies. Been working on for few weeks now, mostly replacing parts. So far, new water fuel separator and new lines to engine., new primer bulb, new engine fuel filter. Today I opened up carbs for a quick clean up and replaced gaskets but only cleaned jets etc.
Still same problem. All I have left is fuel pump and then try external tank. I did a compression check all 125psi. If I turn the fuel enrichment lever on it idles better at start up but still drops after a few seconds and stalls. Plugs all look similar when pulled but I’m no expert. ?

[99yam40]

Make sure the idle timing stays in spec
knowing what 90 you have would help others give info
My C40TLRX had a problem with the Idle timing I had to replace the CDI to get it acting correctly.
But that is not a common problem.
I am hoping you followed the link and sync procedure in your service manual after putting the carbs back on.
that procedure also mentions timing

[robert graham]

My 1999 C90 Yamaha that I bought new had an idle issue several years ago….I removed each idle mixture screw from top of each carb( recording turns out from lightly seated), sprayed carb cleaner into each hole where screw was, blew each with air hose, replaced screws and set to original turns out settings….never any more idle problems….must have been some debris or varnish in those idle mixture circuits …..

[Jonb1032]

Excuse my ignorance here, but boating is new to me. Since I’m having trouble idling, can I put into gear and slightly raise the rpms hence skipping the idle range, hooked up to water that is. I did briefly try that and it also seemed to be extremely rough running and also stalled. I’m starting to think maybe it’s not running on all cylinders. My next plan is leave the fuel side and verify it’s hitting all 3. When In neutral I attempt to open the throttle linkage by hand it still ran rough. Definitely not smooth at all. The plot thickens….

[99yam40]

so you are going to keep all of us wondering what 90 you are talking about for some reason?

and why do you not answer the questions ask of you?

maybe I did not ask properly.
what motor are you dealing with?
did you follow the link and sync procedures?
do you have a service manual for you motor you are working on?

[Jonb1032]

Sorry, it’s a 2004 90TLRC. I was initially hoping it was a simple fuel issue so that’s why I changed the filters etc.. I received the boat from a friend and it ran. It was used by him several times a week. However I was not able to take it out for several months. I have only had one small trip so far. So it’s very discouraging. I did not change any fuel screw setting. Just a basic carb clean making sure jets are clean. Service manual -no. For the few minutes it does run it does have a more pronounced shake than before so that’s why I’m thinking not firing or fuel starve on a cylinder. Been working on this on days off so it’s been taking so long.

[boscoe99]

Sorry, it’s a 2004 90TLRC. I did not change any fuel screw setting. Just a basic carb clean making sure jets are clean.

Were the idle mixture screws removed when the carburetors were cleaned?

[Jonb1032]

No, I just cleaned inside carbs. I removed and cleaned the jets and reassembled with new gaskets. I keep assuming it was a minor fuel issue and it started to snowball. Even though the semi-carb cleaning went well. I probably shouldn’t have jump that far in so soon. None the less the carbs looked good, To good. But I cleaned all holes anyways.

[boscoe99]

No, I just cleaned inside carbs. I removed and cleaned the jets and reassembled with new gaskets. I keep assuming it was a minor fuel issue and it started to snowball. Even though the semi-carb cleaning went well. I probably shouldn’t have jump that far in so soon. None the less the carbs looked good, To good. But I cleaned all holes anyways.

If you did not remove the idle mixture and main jets, disassemble the carburetors completely, and clean all of the parts in a heated ultrasonic cleaner, rodding out the orifices and passageways, you were wasting your time.

There are microscopic holes in the carburetor. Just one of them having a scant piece of debris will cause the motor to not run or to run like crap. All of the clean gasoline in the world getting into the float bowls won't do diddly squat if it can't make its way through the carburetor and on to the motor.

[Jonb1032]

The main jet and the idle circuit jet are inside the bowl, correct. The idle mixture screw is the screw on the outside of the carb.? I did clean remove and clean both jets inside the bowl but did not touch the idle screw outside.

[ausnoelm]

Don't root around speeding up the idle, clean the carbs properly and it will be fine. Poking around washing the bowls and jets is not cleaning a carb. Make sure the fuel tank is clean, or be prepared for a do over.