FT9.9 AE X Cylinder head removal

[99yam40]

Seems there are some parts shown on this that might act as a dash pot, but I am not sure which it would be.
#29 would be my guess, but someone else will have to confirm if that was correct

https://screenshots.firefox.com/lKYr.../www.boats.net

https://www.boats.net/catalog/yamaha...lhx/carburetor

[cleddau1]

So I could not find a solution to the stalling on throttling back so took carb to Yamaha dealer who did a complete overhaul and ultrasonic clean and kindly relieved me of £90. I now have the opposite problem. Engine starts fine when hot or cold. Ticks over nicely once warm. However if I then run it under load for a while say more than 15 minutes when I throttle back to neutral it continues to rev making it impossible to put into gear without switching off and starting again. Cables are all free. Any suggestions welcome and appreciated.

[99yam40]

OK so we are back to a problem when throttling down again or still.

can you tell if the throttle plate is not closing down to the idle position when this problem occurs?

does it move more to the closed position when you turn it off?

How about timing, advanced timing will cause higher RPMs at idle.
timing light would be easy to use to see what the timing is doing

[cleddau1]

Thank you for reply.
Timing is fine and after starting and warming up she ticks over nicely and I can rev in neutral and she goes back to tickover ok. It is only after running under load for a while that the problem occurs. At first I thought the remote cable was not returning properly but the motor is still revving away with the throttle back to the stop. The impression is of over fuelling as soot has appeared around the exhaust and she appears to be using more fuel that previously.

[99yam40]

dumping more fuel into a motor by itself will not cause the RPM to go up, it has to have air too for that fuel to burn.

but you can advance the timing at idle and the RPM will go up.
have you checked with a timing light to see what the actual timing is at idle when running correctly, and then again when it is idling too high to see if there is a difference in the idle timing?

only thing I can think of is timing or the throttle plate is not closing

[panasonic]

Can you get at the engine while running? I would warm up the engine, remove the cowl and disconnect the remote cables and operate the carb by hand with someone steering.
You can also take off the intake silencer and look at the throttle plate.