Engine Trouble Please Help 4 stroking

Discussion in '2-Stroke Engines' started by alpha, May 31, 2012.

  1. alpha

    alpha Member

    im a little bewildered, i wanna use my bike for transportation to work.

    im having issues with what seems to be 4 stroking, ive messed with all of the settings of the needle. i dont know for sure what motor it is, it looks like a jet silver. little head nuts, shorter fins on the side of the head rounded edges on the cylinder compaired to most chinese engines. it has the square gromet for the magneto wires, and came stock with cast intake not the steel welded one. the only one i have seen that looks like it is the jet brand engine. i also dont know what CC it is, the guy who use to own a MB shop that sold these kits told me when i bought it from was a 66/80cc, but when i compaired the dia of the piston to what im sure is a 49/50 cc engine it looks the same and other than a much more stout build as it looks to me looks like a 49 not a 66. so how do you tell the difference between the two?

    as for my problems i have what seems to be the 4 stroking issue as i said above and im not sure what to do, no matter the needle setting i cant get it to run right, either no power or 4 stroking, cant find a medium.

    just playing around with it, i was able to get it to run right with a load on the engine using the back brakes(not always the smartest thing im guessing) but it started smoothing out but soon as i let off the brakes it accelerates then once it gets up about to 75-100 it does the 4 stroking, but at that point i can only do about 20mph.

    when i start from a stop it 4 strokes a little under half all the way up to full throttle.

    im sorry if i may sound a bit short and blunt in past posts im not trying to sound that way at all just busy all the time and dont have the time to make a detailed post like this.:helmet:

  2. Lunardog

    Lunardog Member

    Well you need to start at the basics. Im guessing that its getting spark but, is the plug fouled? Have you checked it? If you run it and pull the plug is it wet? Air filter or exhaust clogged? Leaks around the head gasket or base? Eliminate the most common causes that are simple and quick to check and even if you dont know what you are looking at make a note of what you find after checking the simple things then ask again after you have a little more information. Might help in getting to the bottom of the issue quicker. A picture or two would probably be helpful in getting the engine and carb identified also.
  3. motorpsycho

    motorpsycho Active Member

    there is a VERY tiny difference in size between the 66 cc piston and the 49 cc piston. the only real way to tell is to measure it. you will not be able to tell the size by looking at it, and trying to compair it to another piston.

    what fuel-oil ratio are you using?
    what spark plug are you using?
    what's the spark plug gap set at?
    is the end of the plug brown? Black? silver? wet? dry?
    try running it with the air filter off and see if that makes it run better.
    if so, your air-fuel ratio might be too rich.
    also, make sure that your choke isn't partially closed because that will make it 4 stroke too. the choke plates on the n.t. carbs (assuming that you have an nt) will sometimes loosen up and close on their own.
    it's also possible that you need to re-jet the carb...it sounds like it's running too rich.
    but, start with the simple things before you go re-jetting it.
  4. alpha

    alpha Member

    i will check all of that stuff, im using 60 to one due to break in but normaly use 40:1 with redline oil. i do have an NT carb, but i bought a speed carb witch should be here soon. ill get some pics. i had another NT carb that the choke did close on its own and that just killed the bike, but i have a different carb now and the choke plate is tight now. i need to check the filter, the gap.

    but im using a B6HS NGK. i konw my post is all over the place in a bit of a time squeese
  5. motorpsycho

    motorpsycho Active Member

    60:1 Is too lean. break -in should be 20:1 & then after break -in go to 32:1.
    With fuel-oil ratios, the lower the first number is, the more oil the mix has. 32:1 Has more oil in it than 60:1. 20:1 Has more oil in it than 32:1.
    If you are truly running at 60:1 for break in, you are starving your rings & bearings of oil at a critical time
  6. darwin

    darwin Well-Known Member

    Dirty carb?
  7. alpha

    alpha Member

    lol sorry didnt think about that its 20:1 for some reason i thought it was more with a bigger number, i had to look at my measuring device to figure it out. i will be running 40:1 when im through with my second tank. so about a gallon and a half of fuel will be 20:1 and then to 40:1
  8. alpha

    alpha Member

    carby is clean, but i have a new speed carb comming soon1
  9. Steve w downey

    Steve w downey New Member

    By looking at the head studs 50cc has 6mm studs 80 has 8mm studs this will tell you before you pull the head and save time.
  10. alpha

    alpha Member

    HEY.....well good news, the NT SPEED carb did the trick. i had to bend the float arm down just a hair so it would not flood out. that was one of the biggest problems was the flooding making the bike run really really rich. the bike hauls *** after it gets past 10mph, then it opens up, it tends to hick up around the second power band, but im sure a boost chamber will help with that, i have a friend who had the same issue, it would cut in and out of the top end, and the boost chamber did the trick.

    here is my new motor running good now

    BTW i know i have no filter and i have no idea what to use. any ideas

    i was going to ride it to work but without a filter i didnt know if its ok.
    Last edited: Jun 3, 2012
  11. dodge dude94

    dodge dude94 Member

    Do you have a carb with the two mounting holes?

    If so, you can go to sickbikeparts and get a K&N-style filter. Good for performance, engine filtering, and it looks boss. :D
  12. jaguar

    jaguar Well-Known Member

    I bought a foam filter for a lawnmower and cut it up and glued it back together to fit my carb using silicone sealant. It has lasted a long time.
    By your symptoms I would say the old carb was running too rich (too much gas). You could of leaned it out by lowering the float, lowering the needle, or replacing the main jet with a smaller one.