40hp 2 stroke power problems

[Stuart1975]

Hi All - first post here after being stumped by an problem I'm having .

Its a 1987 40hp 2 stroke - 3 cylinder triple carb motor - which is great and the 4th I've had but.....

Its got in intermittent power drop at full revs - and very lumpy mid range.

I've been advised it could be sticky needle valves not opening to allow fuel to fill the bowls correctly - but I'm wondering if this will be down to age and if so is it a case of can they be cleaned up or is it a case replacing them ?

Sometimes its happy to rev fully - other times it drops power like I've lost power from 1 or 2 carbs ... hit and miss on if will run fine at WOT or not.

Anyone have or had a similar situation or have any advice ?

Thans

[99yam40]

check the fuel pump to see if it is leaking causing #3 to get too much fuel.
If that is not the problem take carbs apart and clean

[Stuart1975]

Thanks - Carbs have been in the ultrasonic bath recently so nice & clean. I'll check the pump in the usual way ( disconnect the outlet and check its pulsing nice & strongly when spinning the motor with the starter).

Failing that it has to be a carb problem - just a question of what !.

Thanks again

[TownsendsFJR1300]

You want to make sure the diaphragm itself (fuel pump) isn't failing or have pin hole in it...

I'd also make sure you access ALL THE carb jets and pull them. Unless you can see light thru them, it don't count...


Another thread that may help, post #6

http://www.yamahaoutboardparts.com/f...tml#post112757