Engine Trouble 4 stroking?

Discussion in '2-Stroke Engines' started by SRPM, May 5, 2015.

  1. SRPM

    SRPM Member

    Hi all I'm new to the forum and hobby. Got the kit on the bike and all dialed in, got the engine all broke in and everything and now I would like to get the engine dialed in just right because I plan on riding it to work. I have the Raw racer 66/88cc engine from gasbike.net (horrible webite) with an improved NT carb. Without the cnc high compression head so stock head.I'm running a 32:1 mixture with some supertech 2 stroke oil form wally world can't find the good stuff and premium gas (92 octane) with a E3.10 spark plug with a gap of about .25

    "Engine Symptoms"
    So when I'm accelerating up to about 15 to 20mph the engine seems to 4stroke (or maybe bogging) until I get up to that speed and will have to pedal to help it get there most of the time but not always, once it hits that speed it seems to gain power but 4strokes on and off up to top speed about 30 where it 4strokes out which to my understanding is normal. When climbing a hill it will have a nice crisp 2stroke sound for a few seconds then it'll 4stroke for a second or two then back to crisp sounding 2stroke then 4stroking and so on all while slowly flossing speed and this hill is nice gradual hill wouldn't be to hard to pedal up. Or is this just normal for these engines.

    So I've played with every clip setting without much improvment. So I got a set of jets #60 to #80. But I have ran into a brick wall. I can't find what the stock jet size is does anyone know on these engines engines/ carbs. I tried measuring it with a tooth pick but jamming it into the hole until it left this sort of lip then compared it to the ones in the set and it seems like it a #68 so I put in a #66 to see if that would help it seemed to a little bit not over noticeable. Seems to run even better when the weather got colder and was about to rain. Also the plug seems to be showing that it is running lean with the #66 spark plug is like a dark gray color and the black carbon on the edge of the plug around the spark plug hole is turning white. I'm super paranoid about running it lean when it has to replace my car for a while. So is there any way to measure jets without buying something so I can know where to start on the jets. Am I just unexperienced and don't need to do anything to the engine. Wrong spark plug maybe or something. Also what would!be a good NGK plug for temps in the 80s to 100s. Anything helps.

  2. Timbone

    Timbone Active Member

    Step 1: remove the air filter and do test runs. I have been reading motorcycle sites and I see where several mechanics suggest just putting some type of plastic enclosure around the air intake. (So I made one of my own and my 4 stroking problems are gone!) With your engine getting a full breath of air, you will know if your mix is too rich.

    The 2 stroke should run best when you find the sweet spot on the throttle intake. Sometimes, WOT is too much air and the motor will 4 stroke out. Sometimes, ou may have to throttle BACK a HAIR to get good engine advance.

    Once you know you have good air, then make sure you have good fuel flow. If your line has a kink or there is fuel foaming due to vibration, your engine will not get enough gas to go up to high RPM brap state.

    I like the NGK B6HS as a plug and it is plenty hot here.
  3. SRPM

    SRPM Member

    Thanks for the input. I'll have to try that when the weather warms up cuz if my understanding is correct when it's colder the air is more dense containing more oxygen thus leaning everything up. I replaced my e3.10 with a NGK B8HS and did a test run in the tiniest drizzle and seemed to run good:grin5:, came back and did a plug chop and it appears to be running lean:shout: now on the stock jet, needle second from top notch. Think the warmer weather would change that, I usually run it on days with temps at or above 70°f and it was ~50- 55°f 60 max today when I did my test runs.:confused:
    Last edited by a moderator: Dec 18, 2015
  4. Slogger

    Slogger Member

    You may want to give the intake manifold joint to the engine and to the carb a little attention. The NTs have notches in their mounting flange that can leak air in and cause your problem. I put an O ring in there and pushed the carb on firmly then tightened the clamp to make sure it isn't leaking.
    Others will tell you they put sealant on the manifold end to help seal it.
    Another thing I found on mine was that the intake manifold mounting flange wasn't very flat or smooth. You can tape some emory cloth flat on a glass surface and mill the flange flat and smooth by sanding it on this flat surface, the reinstall with some gasket sealer goop on it to make sure.
    It's something to try. I doubt a #66 would be too lean on a stock engine, but you never know.
  5. Slogger

    Slogger Member

    Oh, I forgot to mention I had low output and miserable running when I filled er up with premium. Back to regular from now on for me.
  6. SRPM

    SRPM Member

    I went ahead and sealed everything I could so no leaks and more. Also changed the spark plug seems to run better. I think the cylinder but be making contact with the head due to head gasket overly squished.
    I'll have to try regular next time I fill up.
  7. Slogger

    Slogger Member

    My Dax engine came with no head gasket at all. It doesn't leak and the piston doesn't hit anything, so i guess it all good.
  8. SRPM

    SRPM Member

    Cracked her open again last night, it was making a little contact but I just removed as little material from where it was contacting the head problem solved. Would running lean make the engine bog down excessively? Also what's your opinion on the cnc high compression heads?
  9. Slogger

    Slogger Member

    I would back up and ask if you are running it without an air filter installed. There isn't much point to tuning it without one, since it will need one for everyday use. Air filters can have a dramatic effect on my china doll's jetting needs. I was using one like a K&N that came with the SHA. It fell off. The ride home I had good power, more than usual.
    I put one on for a Tomos moped. Like this: http://www.ebay.com/itm/291000159342
    It is held on by a music wire clip and has a real restrictive metal element in it.
    I had to drop 2 jet sizes, from a 66 to a 62 to get it running right. The restrictive filter is good for engine life but bad for total HP. You might as well put yours back on it and then dial it in.
    Anyway, too lean a condition will make it harder to keep running before it warms up, gives a dry raspy exhaust note, almost never 4 strokes, gets very hot, and finally bogs down and seizes the piston.
    Any trouble that seems worse when the engine is cold is a lean condition.
    When it's hot, bogging and 4 stroking or lacking a willingness to rev is usually a rich condition. If you never need the choke in winter, you are probably a little rich.

    I can't help with the head question, I haven't used one since I'm satisfied with the stocker.
  10. SRPM

    SRPM Member

    Filter is on. Its more of a bogging issue I think now don't have much throttle response except at like 3/4 throttle to full throttle. And I couldn't get up the hill I usually make it up by pedaling with the engine.
  11. Slogger

    Slogger Member

    How many hours are on the engine now? Is it fully broken in?
    Mine ran inconsistently during the break in, like it had a mind of its own. (I might have caused some of it, changing oil mix and jetting and stuff)

    If it's ok from 3/4 to full throttle you can try to drop your needle another notch. (Raise the clip) That leans the mixture at lower speeds. If it still isn't lean enough to buzz happily you should go one step leaner on the main jet, put the clip back on a lower (richer) notch and try it. Watch out for a lean run, if you find it's running real lean shut it off and pedal home.
    If your work is a far piece it might be getting hot and sagging as you get there. I don't think these engines are stable temperature-wise for continuous running, they need a cool down break sometimes.
  12. SRPM

    SRPM Member

    I have about 250_300 miles on it not sure about hours but if I had to guess I would say about 50. it's 4.4 miles to work with one big hill ( might get a pic of it up for you guys to see) steep have to pedal with engine like I said before but the rest of the trip is mostly flat and down hill
  13. SRPM

    SRPM Member

    Also I think it's more 3 stroking than 4stroking like when I let off the throttle. If I where to try to put the sound of the engine into words/letter it would be like zzzbbbbbbzzbbbbbzzzzzbbbbbbbbbbzzbbbb instead of a nice zzzzzzzzzzzzzzzzz on the throttle when ithei let off it's more like gugugug and kinda sound like bouncing a metal ball on concrete really fast.
  14. Slogger

    Slogger Member

    Hahaha :)
    The metal ball on concrete sound is disturbing..
    The "zzzbbbbbbzzbbbbbzzzzzbbbbbbbbbbzzbbbb" sounds like you could go leaner, but I hate to say that when you aren't out of the break in zone. You're almost there, but they really do seem to be inconsistent for about 300 odd miles. Mine is, anyway. As the rings seal the pump becomes more and more efficient, the running characteristics will change some.
    I'd run it and read that plug, check for leaks and drag my feet on changes for another 40 miles or so.
    To be safe.
    SRPM likes this.
  15. SRPM

    SRPM Member

    Haha the metal ball thing was just a way to explain it.will do that and keep you guys posted
  16. 66cc

    66cc New Member

  17. Waxxumus

    Waxxumus Member


  18. wildone

    wildone New Member

    when you said put a enclosed plastic around the carb!!! are you talking like a air box on a street bike that feeds the carbs??? just wondering cuz i dont see how that would stop 4 stroking.. as my understanding is 4 stroking is caused by running to rich on top end and only your jetting is gonna effectively change the problem. the best performance mod i did to mine is a dellarto clone carb ( came with new cable 5 sizes of extra jets )and a long pipe expansion chamber i got off of ebay from bicycle_motor_works.com the best advice i would give is junk the oem carb and pipe and the headaches that go with them
    Last edited: Jul 11, 2015