Robin-Subaru lots of carbon in cylinder

Discussion in '4-Stroke Engines' started by moped-dan, Jan 29, 2010.

  1. moped-dan

    moped-dan Guest

    Im doing mantenince on the Robin-Sebaru EHO35 to get her ready for spring. I replaced the spark plug and it looked a little dark but normal. I looked into the cylinder and on the top of the piston it is all black and covered in carbon, is this normal? What could cause this and can I clean it off?

  2. give me vtec

    give me vtec Active Member

    that is always normal on an internal combustion engine.... were you expecting a mirror finish??
  3. GearNut

    GearNut Active Member

    Add some SeaFoam to yer gas. Follow the instructions on the bottle. That'll clean it out while you ride, and get every nook and cranny sparkling.
  4. BigDaddyT

    BigDaddyT Member

    LOL Seafoam is status quo up here. I thought it was just a local thing. Fer the old subaru cars they use Restore too. Seafoam is like a tuneup and Restore is for cars with bad rings and such.
  5. Mountainman

    Mountainman Active Member

    pay no attention

    noticed some carbon
    on top
    but it still does
    pay no attention
    ride that THING

  6. HoughMade

    HoughMade Guest

    Burma Shave​
  7. GearNut

    GearNut Active Member

    "Burma Shave"
  8. seanhan

    seanhan Member

    Moped-Dan It's seems your robin has a carbon footprint !!!!!
    I could't resist !!!
    The best thing you can do for these engines is run the heck out of them !!!!
    the more you use them the longer they last !!!
    well sorta ??
  9. Silvaire

    Silvaire Member


    What you describe may be normal.

    On the other hand, it may not be...

    There are two things I would check - the air cleaner condition and the oil level.

    First, check the air cleaner. Check that both the foam and paper elements are dry and clean. (The EH035 does not use an oiled foam element.) A dirty air filter will cause an engine to run too rich, causing soot to form on the piston and combustion chamber. An overly rich mixture will also wash the the oil film off of the cylinder walls, which causes wear leading to oil burning.

    Second, make sure you have the proper amount of oil in the engine. Either too much or too little oil will cause problems. Too much oil in the crankcase will cause the engine to blow oil out the breather tube and into the intake, causing carbon build up.
  10. moped-dan

    moped-dan Guest

    Thanks for all the advice... MM i love the poem.

    Silvaire I have the right amount of oil and the air cleaners are dry so I think ill let it be. The engine is running great I was just worried to much carbon would cause a problem.
  11. GearNut

    GearNut Active Member

    An even film of carbon is normal. If it is all chunky and thick, like 1/6" or 1 mm thick in spots, then you have problems.
  12. Old Bob

    Old Bob Member

    Under normal conditions it builds to a certain point and doesn't build any more.The mere presence of carbon deposits does not mean there is a problem. Most people would load their pants if they saw the inside of their car engine after 50,000 miles.
  13. BigDaddyT

    BigDaddyT Member

    I was told by an old timer to run the rpms up and drop a teaspoon of water in the carb and it will decarbon the engine somewhat.
  14. Happy Valley

    Happy Valley Active Member

    Yes, they do carbon the piston crown. I've conversed with Robin/Subaru factory service techs on this and told not to sweat it, about what I expected. I believe in part it has to do with the EPA compliancy and recycling gases back through the cyclinder.

    I also believe Seafoam, in moderation, is the EHO35's friend.
  15. GearNut

    GearNut Active Member

    Any gasoline powered ICE engine develops carbon build up. Gas is, afterall, a carbon based fuel. Petroleum, AKA dead dinosaurs and plant matter.
  16. arceeguy

    arceeguy Active Member

    I agree with the others, not a big deal unless it is causing problems with pre-ignition.

    I would also refrain from any fuel additives. My thinking is that if the solvent is powerful enough to clean carbon off of the piston, what is the solvent doing to the lubrication film on the cylinder walls?
  17. Happy Valley

    Happy Valley Active Member

    To mitigate carbonizing I use Seafoam but strictly as an upper cylinder treatment IE: a teaspoon misted into the intake of the warmed engine with near WOT once or perhaps a couple of times a year depending on engine hours.