Help with yamaha 40 2 stroke!

[daverowlands]

Hello all,

Just purchased a used yamaha 40 hp approx 1994 (see vid)
- http://www.youtube.com/watch?v=Y6nMHPeu1GI, Ran sweet as a nut yesterday for around half an hour then started to run rough and misfire, the engine was pumping water ok and the spark seams good. Fitted new spark plugs but when i pulled the lower one out after 5 mins running noticed vapour coming out of the cylinder possibly steam? bottom cyl water leak? after pulling the plugs out all looked the same, a small amount of oil on them. I was thinking the tank had sat around for a while and some crap could have got into a carb after half hours run? only other things i can think of is bottom cyl getting water in it or the CDI pack is playing up. Does anyone know if a yam dealer can do a electronic diagnostic of this engine?

Many thanks

 

[robert graham]

Re: Help with yamaha 40 2 stroke!

drain each carb onto a clean white rag to see what's in it, then with drain plugs out, pump primer bulb to "flush out" carb/float needles. check fuel line from pick up in tank, primer bulb, fuel quick disconnect on motor, fuel filter, fuel pump. may need to clean carbs/jets. Good Luck!

 

[daverowlands]

Re: Help with yamaha 40 2 stroke!

Thanks for your reply, I will do a carb clean, can the carbs be drained when still on the motor? I ask this since you mentioned the drain plugs?

Thanks

 

[99yam40]

Re: Help with yamaha 40 2 stroke!

yes they can. There are brass plugs on the bottom right hand side of the bowls. left hand side if you are facing the front of the motor. should be a 10MM head. Don't forget to clean the tank and put in fresh gas to keep from getting stuff back into the carbs after you clean them.

 

[daverowlands]

Re: Help with yamaha 40 2 stroke!

Thanks a lot for your advice, engine seamed to run better after draining the carbs, is this a good enough clean or do i need to take the carbs off and clean them fully?

 

[robert graham]

Re: Help with yamaha 40 2 stroke!

I drain the carbs fairly often just to remove any water or junk in them(takes maybe 5 minutes once you learn to do it), but draining carbs won't unplug a jet, so you may need to remove/clean carbs or have it done. drain carbs (onto a clean white rag to see what's in them), fairly regular, use Stabil Marine all the time and add a fuel/water seperator(Walmart $27) and you should be in great shape, fuel wise. my motor is a 1999 Yamaha 90C and the carbs have never been cleaned and it runs like a champ. just good preventive maintenance! Good Luck!