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2008 Yamaha F40 40hp 4 stroke bogging down at throttle

bigtime_mcalpine

Regular Contributor
I picked up a motor for my local sailing club (used) and I think I'm paying for my good deed. The motor is VERY temperamental. Starts and idles fine but needs a very slow steady hand to throttle up and even then, many times it bogs down and sometimes stalls.

Some googling pointed me to a few links where owners had success re-jetting the main jet, replacing the (apparently) undersized jet with a compatible one from an F25 of same vintage.

Not sure I'm a big fan of that approach but multiple stories point to this actually working.

My first thought was, would a cleaning of the main jets not be a more prudent approach?

Any of you have similar tales of woe with this engine?
 
I can confirm that on at least two F40's the only way to get the motor up and running was to use bigger jets. The F25 jets.

Slow to accelerate indicates the accelerator circuit is clogged.

You might get lucky where the motor will run just fine after a thorough cleaning. In an ultrasonic cleaner perhaps.
 
I can confirm that on at least two F40's the only way to get the motor up and running was to use bigger jets. The F25 jets.

Slow to accelerate indicates the accelerator circuit is clogged.

You might get lucky where the motor will run just fine after a thorough cleaning. In an ultrasonic cleaner perhaps.

thank you, exactly what I was looking to hear before proceeding.
 
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