2002 Yamaha F40TLRA Pilot Screw Question

[bigbeeus]

What does the pilot screw do? How many turns out should it be set to initially? How to know when it is set correctly?

Trying to teach myself how to rebuild the carbs on my F40. Thanks for the education.

[robert graham]

It adjusts the idle mixture of air/fuel….the screws are set at the factory….usually 1-1/2 to 2 turns out from lightly seated. Just screw it in until lightly seated, counting and recording the turns, then you can re-set them after carb cleaning. Screws can be adjusted slightly for smoothest idle…

[boscoe99]

The base setting for the F40 is 2.5 turns out from being lightly seated. Plus or minus 0.5 turn.

Fully disassemble the carburetor to the extent that it will come apart. Needs to be cleaned in a heated ultrasonic cleaner using a good cleaning solution. Every passageway and orifice then being cleaned and confirmed to be open.

The accelerator pump nozzle is particularly difficult to clean. There is a modification that might help if the nozzle cannot be cleaned.

[99yam40]

you really need to get a service manual for your motor if you plan on working on it yourself.
4 stroke motors are not all set the same as old 2 strokes motors ( no good simple rule of thumb to go by) , so having that info in hand for your motor is a good thing to have

[boscoe99]

Making an adjustment to the idle mixture screw while the motor is running is something that you will feel. All but impossible to put into words on paper. Might take a bit of fiddling since there are three carburetors. The idle mixture screw may not end up being the same on all three carburetors.