1990 Yamaha 40hp carb issues...

[SiLiconD17]

Hello all, I just bought a 16' semi-V aluminum bass boat with a 1990 40hp Yamaha 2 stroke 3 cylinder on it. It cranks fine and everything and will run for a second, but you can smell that it's got old gas in the carburetors (it had sat for about a year). I know this unit is oil injected, but I'm not sure how that works exactly as I am used to working on pre-mixed carbureted 2 strokes.

It's my assumption that it will need a carb rebuild job, but doesn't oil injection squirt oil directly into the block instead of into the carburetor? Or does it simply mix with the gasoline and run through the jets in the carbs like a normal pre-mix outboard? I ask because if only gasoline is running through the carburetors, there should be no reason that they're gummed up and needing a rebuild.

I'll have to look into it more tomorrow when I have light to see... Thanks for your help!

 

[bgbass.1]

Re: 1990 Yamaha 40hp carb issues...

the oil mixes into carb. you should rebuild carbs.then decarbon pistons mix seafom withyour gas that will help remove any gunk left over.

 

[rodbolt]

Re: 1990 Yamaha 40hp carb issues...

oil on that yamaha is injected into the reed box aft of the carb, pure gasoline is all thats supposed to be in the carb.
gas will dry and form all kinds of nasties.
time for a good cleaning and maybe even replace the fuel pump as they dont last forever and if the rubber fails it can cause a rod to exit the block.

 

[SiLiconD17]

Re: 1990 Yamaha 40hp carb issues...

Thanks for the info. I changed the plugs today and tried a few things. It cranks when you pour gas directly into the cylinders where the plugs screw in, so it's got to be the carbs. It looks like I'm in for a rebuild...