Spark Plug Issues

Discussion in '2-Stroke Engines' started by Alson, Jun 14, 2010.

  1. Alson

    Alson Member

    I read you thread and know Im going to gap my spark plug at .024 instead of what my manual sugests .036. What do the smaller gap do, compared to the big gap

  2. AussieSteve

    AussieSteve Active Member

    With a larger gap, it's harder for the CDI to produce a strong spark, but more of the spark is in contact with the mixture.
    A smaller gap results in a stronger spark, but less spark/mixture contact area.
    It's a balance between the two.
    A 0.024", (0.6mm), gap seems to work pretty well with these engines. Some guys that use the white wire for lighting, (which draws power from the ignition winding), set the plug gap at 0.020", (0.5mm), to compensate for the weaker spark.
    0.036", (0.9mm), is a very large gap. These CDIs aren't very strong, so a smaller gap would definitely be better than that.
  3. Alson

    Alson Member

    changing gap and better plug

    My engine sputters, I moved the C-clip up, then lost power. So I put it back, got a lot of power, but still sputters when I dont give it throtel. Im was told to go with a better plug NGK B6HS but try a B5 first it might take care of the sputter, is what I was told, I'll see
  4. Alson

    Alson Member

    more air flow to get rid of sputter

    If the sputter doesent go away by useing the NGK B5HS, then I thought I should go wjth a high performance air filter, it would lean it just a little, might help the sputter
  5. Alson

    Alson Member

    more air flow to get rid of sputter

    If the sputter doesent go away by useing the NGK B5HS, then I thought I should go wjth a high performance air filter, it would lean it just a little, might help the sputter
  6. AussieSteve

    AussieSteve Active Member

    Not real sure what you mean by 'sputter'. Missing? Only at idle?

    Still, if you're using the stock plug, that could well be the problem. Fit the B6HS and see how it goes. (I never even fitted the stock plug after reading the recommendations here.)

    A better air filter isn't a bad idea, but that won't be causing the problem. These engines can be tuned pretty well with the stock one.

    Run the B6HS for a bit, then pull it out and check the colour for an overall indication of your mixture.
  7. Alson

    Alson Member

    Engine still sputters

    I put a NGK B6 in and it seems the same, I took my air cover off and seen oil in the filter, its spitting oil and gas back in the air filter. I moved the c-clip to lean it but lost a lot of loaer but it didnt sputter like it did, so I put back to second from top it sputters when I dont give it throttel, but when I give it throuttel it runs real good. No idea how to fix it, any sugestions would be apprecheated
  8. AussieSteve

    AussieSteve Active Member

    It's perfectly normal for these engines to blow a little fuel/oil back out of the carb. They're what's known as a 'port scavenged' engine. There is no reed valve or other means of stopping some mixture being blown back as the piston drops, before the intake port is blocked by the piston. Some mixture is also blown out the exhaust during the cycle. (That's the purpose of an expansion chamber. The tuned length provides a reflected pulse from the rear of the chamber that pushes the mix back into the combustion chamber.)

    Odd that it's only real rich only at idle and not through a bit more of the rev range.
    Usually, if mid-throttle mixture is OK, these things idle surprisingly well, considering the carb has no idle circuit.

    Maybe the float level is set too high. It should be set at 21mm. The procedure for checking is described in NT Carb Tuning Basics.

    There isn't any fuel in the float, is there?

    Have you removed and cleaned the carb with compressed air? Might be a bit of c r a p in the float needle seat, although that would usually affect more of the rev range.
  9. Alson

    Alson Member


    I took my biger jet out and put the stock jet in jt, it runs the same. Ill try to move the flot deal down a bit and see if that will help, I cant see the pitcher of the flot adkustment that well, Ill give it a shot
  10. AussieSteve

    AussieSteve Active Member

    No, it wasn't the clearest. I got a bit of glare from the flash.
    With the carb upside-down and gasket removed, measure from the gasket seating face to the highest part of the float. Should be 21mm.

    I saw your post in 'NT Carb Tuning Basics'. Hopefully the other carb will work properly. Then you know it was the float level.

    Good luck.
  11. Alson

    Alson Member

    trouble shooting carb

    I put the brass arms that regulates the float hight from my stock carb, which looks much higher. Took it for a ride, and the sputter is gone, it runs very good and cruses nice in slow movement. I dident have a mm mesurment, but runs good but seems like I lost a litt,e top end, when Im going slow and open it up it bogs then goes. I dont know if its to ,ean, I didnt take the spark plug out and look yet. If its lean should I bend the brass things down a bit. When I have the carb upside down the float and the the top of tbe brass valve are flush, your pitcher it was up above the float a little. Ill check the plug and go from there
  12. Alson

    Alson Member

    Thanks Steve for the info, jt was tbe float level
  13. Alson

    Alson Member

    My plug is a light chocklet brown, like nesley quick
  14. AussieSteve

    AussieSteve Active Member

    Good timing. I was just about to reply. Been pretty busy.

    I knew that it had to be something simple. (There's nothing complex in these engines.)
    I'm glad it's sorted.

    Regarding final adjustment, it's best to set the float at about 21mm, then use the slide needle height and main jet size to get things just right. Altering the float level to adjust the mixure will lead to problems.

    The plug colour doesn't sound too bad, possibly very slightly rich. If it was lean the plug would be grey or whitish.

    Best to do plug chops at mid-throttle and WOT with a new plug, as described in 'NT Carb Tuning Basics', to do the final adjustments.

    Good luck.

    P.S. It's better that the mixture is slightly rich, rather than lean. If it's not 4-stroking, I wouldn't be overly concerned if I were you.
  15. Alson

    Alson Member

    It seems like I lost just a little top end about 3-5 mph, I dont have a speeddometer, but I can tell, I thought about lowering it just a little, I dont knowl mabe I should just leave it a,one ,ike you said, see I realy dont know if its set right, I had no mm mearsUment deal to measure jt. I looked real close at your pitcher and your nedel valve was just a little up from your float, mines even wjth the float, makes me think jt might be why I lost a little top end
  16. AussieSteve

    AussieSteve Active Member

    Still best to actually measure it if you can.

    Then you should ideally do what I suggested. Anything else is just messing around.
    Hopefully I don't sound rude, but i've already said it all.

    I do re-iterate, though, don't try to tune your bike by float level adjustment. Just set it at 21mm. (Buy a steel rule if necesary, they're only a couple of bucks.)
  17. Alson

    Alson Member

    Alright, Steve, thanks, Alvin
  18. AussieSteve

    AussieSteve Active Member

    No worries, glad I could help.
  19. Alson

    Alson Member


    Thanks again, you realy did help
  20. Fabian

    Fabian Well-Known Member

    Hi Alson,

    Please be careful with your comment: "I took my bigger jet out and put the stock jet in jt, it runs the same."

    From my experience, the engine may appear to run the same, but if it runs well on the larger jet and you replace it with a smaller jet, it will only run hotter, and most likely detonate, causing the connecting rod big end bearing to fail.

    I've had 5 engines all fail with exactly this same problem (big end connecting rod bearing failure) and since replacing the main jet with a larger Dellorto No 84 (through trial and re-trial) i've not had any more engine failures.
    Every one of my engines would fail at 700 kilometers (approx 450 miles). The distance figure of 700 was so repeatable it was almost laughable.

    Last edited: Jun 24, 2010