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  1. #1

    Question Yamaha 6, used plugs totally different

    Recently doing my pre winter tune up. Removed plugs; upper looked ok, bottom coated with very dry, brown powder (almost like dried up brownie), looks like a lot of rust. Can that much moisture get passed the fuel filter AND the carbureator? I use my outboard almost daily ....I usually tilt it up overnight etc..Is there a possibility that over our wet winter the humidity worked it way up the h2o intake, passed the impeller and condensated in the engine and caused the combustion chamber/pistons to rust? Thanks

  2. #2

    Default Re: Yamaha 6, used plugs totally different

    Quote Originally Posted by jtmeade View Post
    Recently doing my pre winter tune up. Removed plugs; upper looked ok, bottom coated with very dry, brown powder (almost like dried up brownie), looks like a lot of rust. Can that much moisture get passed the fuel filter AND the carbureator? I use my outboard almost daily ....I usually tilt it up overnight etc..Is there a possibility that over our wet winter the humidity worked it way up the h2o intake, passed the impeller and condensated in the engine and caused the combustion chamber/pistons to rust? Thanks
    The brown gunk is carbon build up. And if you're only seeing this on 1 or 2 plugs verse all plugs, this carbon is a good indication the carb timing and sync is off. Too rich a mix being delivered to bottom cylinders. When mix enters the cylinder pre-ignition but does not completely burn (combust), what remains in the cylinder coats the piston head, cylinders, and plugs. Over time it hardens. Moisture isn't getting past the filter, carbs, etc. This residue is where the moisture is coming from. Need to reset your carbs and decarb the engine. Use yamaha ringfree or seafoam. I'd do a shock treatment, then run a decarb fuel additive with every fuel fill up for maintenance.

  3. #3

    Default Re: Yamaha 6, used plugs totally different

    Quote Originally Posted by ClassicAQ View Post
    The brown gunk is carbon build up. And if you're only seeing this on 1 or 2 plugs verse all plugs, this carbon is a good indication the carb timing and sync is off. Too rich a mix being delivered to bottom cylinders. When mix enters the cylinder pre-ignition but does not completely burn (combust), what remains in the cylinder coats the piston head, cylinders, and plugs. Over time it hardens. Moisture isn't getting past the filter, carbs, etc. This residue is where the moisture is coming from. Need to reset your carbs and decarb the engine. Use yamaha ringfree or seafoam. I'd do a shock treatment, then run a decarb fuel additive with every fuel fill up for maintenance.
    I did a small experiment: bought new plugs, gapped, installed carefullly. Bought new tank, fuel line, new fuel, mixed properly, new fuel filter. Drove dingy from shore to my anchored out boat, 100yards, for two round trips. Removed plugs this morning and the brown gunk was already back. So seems like your diagnosis rings true....being ignorant about carbureators ...are there two different jets that supply each of the pistons?

  4. #4

    Default Re: Yamaha 6, used plugs totally different

    Quote Originally Posted by jtmeade View Post
    ...are there two different jets that supply each of the pistons?
    Reply back with your engines model number and year and I'll let you know.

  5. #5
    Join Date
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    Default Re: Yamaha 6, used plugs totally different

    On a 6 hp there is one carburetor that feeds both cylinders.-----Do a compression test.

  6. #6

    Default Re: Yamaha 6, used plugs totally different

    hard to read:
    1996 Yamaha 6H6 2 cycl 6MSHU S 0311following numbers rubbed off.
    Did a little clean up, got rid of old gas and old tank, installed new tank, with new fuel with Quicksilver 2 stroke oil and Stabilizer, new fuel line, new fuel filter.
    Should I still add the Yamalube to this mixture? Are they all compatible?

  7. #7

    Default Re: Yamaha 6, used plugs totally different

    Quote Originally Posted by jtmeade View Post
    ...are there two different jets that supply each of the pistons?
    No. You've got 1 carburetor with 2 jets that meter the fuel/air mix for 2 cylinders. Since you're only seeing carbon build up on the bottom cylinder plug, I'm guessing this is because of gravity. Have you pulled carb and jets to clean?


    Quote Originally Posted by jtmeade View Post
    Should I still add the Yamalube to this mixture? Are they all compatible?
    Sounds like you already mixed fuel with quicksilver 2 stroke oil. Are you asking if you should add more oil using yamalube 2 stroke oil?? There is no difference between yamalube 2 stroke oil and quicksilver 2 stroke oil, other than the brand name and price. So yes, they are compatible, if this is what your asking. I wouldn't mix different fuel stabilizers together though. Each brand of fuel stabilizer can have its own dose of stabilizer per gallon of fuel. I don't think anything bad will happen. Worst case is you mistakenly add too much stabilizer, in which case your engine is now running on a shock treatment instead of routine treatment.

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