Is my fuel air mixture good based on spark plug?

Discussion in 'General Questions' started by StrontiumEthics, Aug 7, 2010.

  1. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Here is a picture of my spark plug after I ran the engine for 5 min and went full throttle then killed the engine while in full throttle. and cool down for 30 mins. I would like to know if my mixture is good.
     

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  2. a/c man

    a/c man Member

    Looks a little on the rich side to me.
    How's it running in your opinion?
    Is it 4 stroking or stuttering at full throttle?
    The picture would tell a little more from a side view of the plug.
    You want a chocolate tan color on the insulator.
    I'd probably lean the main jet a little.
     
  3. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Its Very funny. I just adjusted the Needle and took that last picture from the first post. Before that point the engine was stuttering @ Full throttle when I rode. I was getting the idea that it needed a little more fuel. So I lowered the e-clip to the 3rd out of 4th slot on the needle, and tested it. I didn't really get a chance to test it with the engine on the 3rd notch (The two attached pictures) because it began to get dark outside. But while the engine was on the 2nd notch it stuttered while riding at full throttle. Here is the picture from the side you requested.
     

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  4. a/c man

    a/c man Member

    Oh yea, way to dark and oily. You'll foul that plug quickly that rich.
    Remember that the needle jet will only regulate the fuel mixture to about 2/3 throttle. You can move the clip to the top notch and still be running too rich at wide open throttle with too large of a main jet.
    When you did your plug chop test at wide open throttle the needle jet didn't even come into play.
    I really think it's time to play the which size main jet do I need game. Experimenting by soldering the jet shut and re-drilling is the easiest, quickest and cheepest way.
    There's lots of posts here about that or e mail me if you want.
    I've got mine just right and the difference is remarkable.

    Tim
    Boell4grumpa@aol.com .....if you need to
     
  5. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Wow! Really? But very strange. When I had the E-clip on the second notch and did the same test the spark plug came out pretty dry, not so oily. So do you recommend going down on my main jet? I don't mind getting some jets from SBP? But from what do I start with? which jet do I have now?
     
    Last edited: Aug 7, 2010
  6. GearNut

    GearNut Active Member

    The most common jet size is a 70.
    I say most common size because the actual jet size seems to vary a little with different kits, manufacturers, and the particular day of the week that the carburetor was assembled.
     
  7. a/c man

    a/c man Member

    I really should have asked what ratio you are mixing you gas and oil.
    A "thick" mix will look darker than a 24:1 mix for example.
    Like GearNut said stock is around #70 (.027 inches)
    Most stock jets run too rich.
    Try a #68 jet see how it works.
    If you want to try drilling here's the resource I use for converting
    drill size to both millimeters and decimal inches.
    It's about half way down the page .DRILL BIT CONVERSION TABLE
    http://en.wikipedia.org/wiki/Drill_bit_sizes
     
  8. motorpsycho

    motorpsycho Active Member

    yes, also remember that when you go to a smaller jet, one number size difference can make a huge difference in the air/fuel ratio. you may have a 70 jet now, but if you drop to say, a 65...that's dropping way too many sizes all at once. when you lean out a carb by changing the jet size, you need to go in tiny increments.
    like a/c man said...if you have a 70 jet, only drop down 2 sizes to a 68 and try it.
    i think i need to re-jet one of my carbs too, but i am running 16:1 gas/oil mix for the break in period so i won't really know if i have to lean it out until i can drop to 20:1 or 32:1 gas/oil mix.
     
  9. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    As of now I am running a 20:1 ratio and I put the notch up to the Second to first notch. and ran the engine for quiet a while and then let it cooled and took this picture of my spark plug. Tell me what you guys think. I was going full throttle a lot while riding.

    PS: Something strange started to happen. While riding when I release the throttle it took a little while longer for the bike to idle. Perhaps an air leak in the carb?
     

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    Last edited: Aug 8, 2010
  10. a/c man

    a/c man Member

    It looks better.
    How did it run?
     
  11. GearNut

    GearNut Active Member

    Grey with a hint of brown is definately better. The grey is caused by additives in the pre-mix oil that you are using. nothing wrong with it. If it were silver I would be worried.
    Silver is burnt aluminum from the crown of the piston getting deposited onto the spark plug. An air leak will cause a lingering high idle that slowly drops down to normal. Check it out before trying to adjust the fuel/ air mixture any further.
     
  12. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Lol. So far today it ran very nicely. It stopped the stuttering at high RPM when the engine was nice and hot. How Can I get rid of this Carb leak? Its really annoying when I want to slow down and clutch and the engine keeps revving. It wasn't like that before.
     
  13. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    I have read in the forum I can get an O ring. But is there a something else that I can do with the carb? One time I tried putting grease along the exposed area but after a while it got really dirty so I don't know if its a good idea.
     
  14. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    It ran great today.
     
  15. GearNut

    GearNut Active Member

    Do not do the o-ring trick!
    The only way it will work is if you push really hard on the carburetor to compress the o-ring and hold it there while you tighten the mounting clamp.
    If the o-ring is not made out of the correct rubber (Buna-N) it will react with the fuel and get soft and swell up to the point where it will not fit in the space it has to live in, eventually getting sucked into the engine.

    A thin coating of Hylomar on the intake manifold, will seal it up very well and be easy to clean up in the future if needed. A q-tip dipped in acetone works well for spreading it around upon application, and a rag wetted with acetone removes it.
     
  16. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Where exactly am I sealing up on the carb? Just the manifold? While I am there should I replace the studs that hold the manifold into the head? They got loose once already.
     
  17. GearNut

    GearNut Active Member

    You are sealing the manifold to cylinder and the carburetor to manifold, both ends of the manifold really.
    You can replace the manifold to cylinder studs if you want to, but few folks ever have a problem with them. As for coming loose, these engines seem to vibrate everything loose, even the fillings in your teeth.
    Loc-tite 242 Blue is a common thread locker used on the offending fastners.
    Some folks swear by it, some swear at it.
    Those that swear by it usually do a visual inspection of the bike approximately before each ride, fixing or adjusting things as they get to them.
    Those that swear at it typically go over the entire bike frequently and religiously keeping everything is tip top shape,torque, and tune.
     
  18. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    SO Do I still use the normal intake gasket?
     
  19. a/c man

    a/c man Member

    Keep the intake gasket on.
    I also use Hylomar gasket sealer on my bike and car (water pump)
    Coat the gasket but don't over-do it with the goo.
    Nobody has asked, but have you checked your throttle, throttle cable, cable tensioner, and throttle slide to insure that its not binding in any way to return the throttle back to idle? It should return back crisply and you can hear the throttle slide bottom out if the engine isn't running and you goose the throttle and let it go out of your hand.
    That spring inside the carb isn't big or strong enough to overcome a lot of resistance in the throttle twist handle, cable, and throttle slide set up.
    Just a thought ..trying to cover all the bases buddy.
    Also that cap on top the carb is crappy and will distort if you tighten it down just a little too much with channel locks, Mine has hung wide open on me once or twice and scared the poo out of me.

    GLAD TO HEAR YOU GOT IT RUNNING BETTER.
    These bikes are like an ongoing science experiment.
    TIM
     
  20. StrontiumEthics

    StrontiumEthics Motored Bikes Sponsor

    Oh ok. The throttle is what i have to look into. Is there a stronger spring that i can use instead? I believe it comes down enough. But I just installed some silicone gasket sealant on the intake gasket, and the intake manifold into the carb. As of now i'm letting it dry. Tomorrow I will be checking the throttle cable.
     
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