06' F40TLR pilot jet guestion

[handle59]

I have been led in this direction to seek out a particular member that has re jeted this specific motor with good results. I have cleaned carbs repeatedly, run treated fuel, synced carbs and the motor still seems to be running lean. I believe the pilot jet is the problem but mid range is also acting up.
Runs a little better after cleaning but goes down hill fast. It may have run ok from the factory but it seems that any build up (ethanol residue) on the jets will make this motor run poorly. I don't use this motorboat very much which I know is one of the problems but when I do use it I need it to run correctly!
Knowledge is power, please enlighten me.

[boscoe99]

What do you want to know?

First thing to be aware of is that your F40 uses a #38 idle jet. Earlier F40's used a #40 idle jet. The running quality of the motor when down hill when the smaller jet was introduced. Ostensibly to reduce emissions.

I took a number of crappy running F40's having #38 idle jets and changed to them to a #45 jet. Why? Because I had a bunch of #45 jets available. At the same time I installed a bigger main jet. Why? Because I had them and thought I would install them just to see what happened.

The results were nothing short of miraculous. The motor started, idled, accelerated and ran at full power with nary a problem. Now I did thoroughly clean the carburetors prior to installation of the bigger jets and made sure that all passageways were free and clear and that the accelerator pump and its nozzle were operating as they are supposed to. There is a modification available for the nozzle if it is clogged and the clog cannot be cleared. Also, there is a modification available to improve the chances of successfully cleaning those little buggars.

I used a heated ultrasonic carb cleaner with Yamaha carb cleaner as the solution.

[99yam40]

seems like I remember him saying one or more of the jets may have come from a 25hp motor, but I could be wrong

[handle59]

What size main jet did you increase to?

[boscoe99]

seems like I remember him saying one or more of the jets may have come from a 25hp motor, but I could be wrong

Damn good memory. They were from F25's.

[boscoe99]

What size main jet did you increase to?

A #108. Jet used from the factory is a #95. Like I said I am not sure if the larger main jet is even needed. It did not hurt the motor however. Without putting an O2 sensor on the motor I cannot say how it really affected the air fuel ratio at high power.

If you don't mind playing with the carburetors I would first install just the oversize idle jets. Then if the motor is not what you want try a bigger main jet.

[handle59]

I will go ahead with the larger pilot jets #45, may increase the mains to #100 not sure yet. The motor always seemed to run well wide open but lately the midrange is missing a little along with poor idle. What jets is the motor running on at half throttle? Mains or pilots or both? Is there any additive you would recommend over another to help keep carbs running clean? I have tried a little bit of everything without much success.
Thanks for you input.

[boscoe99]

See this thread for a theory of operation of the carburetors. It shows how air is mixed with the gasoline and introduced into the motor. It changes with the throttle opening.

http://www.yamahaoutboardparts.com/f...d-th27082.html

The increased idle jet will allow a bit more gasoline into the motor at both idle and at power. Might just want to go with the larger idle jet at first. Plus, I need someone to do this to tell us how the motor responds.

I got the jets from jetsrus.com at a fraction of the price that Yamaha charges. If there is doubt about what style is needed you can send them a photo via and email and he can help you.

mike@jetsrus.com

Keihin carburetor jets and parts main jet slow air pilot kit

[Tony Harper]

Morning Boscoe, can you please elaborate a bit more about the modification for the blocked accelerator pump nozzle & best way to clean them, is this mod available on paper to view??
Sometimes these blocked nozzles have debris floating around inside of them, I have used ultrasonic bath cleaners & this seams the best way, but even then it may take quite a long time to clear properly.
Cheers from down under Aus.

[boscoe99]

Morning Boscoe, can you please elaborate a bit more about the modification for the blocked accelerator pump nozzle & best way to clean them, is this mod available on paper to view??
Sometimes these blocked nozzles have debris floating around inside of them, I have used ultrasonic bath cleaners & this seams the best way, but even then it may take quite a long time to clear properly.
Cheers from down under Aus.

Cheers from up over USA.

Send me your email address. PM if you wish.

[Tony Harper]

Have pm'D you Boscoe, thanks