Idle mixture screws/jets

[robert graham]

O.K., I decided to crank up my 1999 Yamaha C90 today for the first time this season.....never had any problems or issues with this motor since new....but today it was idling rough and cutting off.....I'm thinking I've been real lucky with this motor so far but may need to find a mechanic....But I did recall reading on here about those idle mixture screws on top of each carb, so I decided to pull each one out, taking note of the 1-1/2 turns out from lightly seated.....sprayed some carb cleaner in each one, replaced the jets......Now it idles just like it's supposed to!......Man, that was easy!"....My question to the experts is: should I spray these jets out now and then just to keep them clean or just wait for some idle symptoms?......I'd appreciate any thoughts or ideas on this....thanks!

[boscoe99]

If what you did solved the problem then I would simply leave well enough alone. Maybe you just had a build up of deposits on the needle valve or seat area that the cleaner removed. In which case you got lucky.

The use of ring free or something similar should help to keep deposit build ups to a minimum. I would just retry the procedure you used, only if and when necessary. Otherwise you might put abnormal wear and tear on the carburetor by removing and reinstalling parts. Other opinions may vary.

Did you say that you are the original owner? Interesting to hear that your needle valves were 1-1/2 half turns out from being lightly seated. Specs call for 1-1/4 turns out, plus or minus 1/4 turn. So, yours were in specs, using the allowable tolerances.

[robert graham]

If what you did solved the problem then I would simply leave well enough alone. Maybe you just had a build up of deposits on the needle valve or seat area that the cleaner removed. In which case you got lucky.

The use of ring free or something similar should help to keep deposit build ups to a minimum. I would just retry the procedure you used, only if and when necessary. Otherwise you might put abnormal wear and tear on the carburetor by removing and reinstalling parts. Other opinions may vary.

Did you say that you are the original owner? Interesting to hear that your needle valves were 1-1/2 half turns out from being lightly seated. Specs call for 1-1/4 turns out, plus or minus 1/4 turn. So, yours were in specs, using the allowable tolerances.

Thanks for the feedback....I'm the original owner, use Ringfree and Stabil all the time, and drain carbs for extended shut-downs, never a problem! The needles screwed and unscrewed easily with the spring tension the only resistance, and they looked very clean. Each was about 1-1/2 turns out, give or take just a bit....With the motor idling just fine I moved them a little back and forth to listen for any changes.....didn't seem to make any difference just to my ear....wonder how the factory sets these? Maybe not all that critical. Tell you this much, I wouldn't swap a guy even, my C90 for a brand new 90HP 4 stroke....Guess I'll just leave these needles alone for another 5 or 10 years!...Thanks again!