Engine now backing way down

Discussion in '2-Stroke Engines' started by LabDude661, Sep 29, 2008.

  1. LabDude661

    LabDude661 New Member

    My 70cc 2-stroke was running great. I started to notice a little bit being taken off the top end recently. It smoothed way out but got slower and slower. The other day I was cruising back from the store at like 18 mph (usualy in-town cruising speed for me) and I decided to open up a bit and check my top end. I got to about 25 and it started to back off. Then it jerked back a few times and then it sounded like it was getting mad at me so I slowed down. It ran alright at the lower speed. I though maybe I was running too lean, so I choked it a bit. Then my top end dropped to like 20. I took my carb apart, the jet is clean and there are no chuncks anywhere. The float had filled with a little fuel somehow. I got the fuel out of it and ran it down the street. Did not solve the problem. Then I took my needle down a notch to richen the fuel. Same problem and a really low top end. So I got brave and took the clip up to the leanest setting. Got up to 25 and was I surprised to hear... A BACKFIRE! Startled me more than a little. It was bogging in and out and lurching. I checked the exaust and it was clear all the way through. The only system I haven't check is the ignition system. Has anyone had any problems like this with the magneto or CDI? I don't want to just start buying stuff. That kind of defeats the purpose of these things you know. Any help would be appreciated.

  2. funker

    funker Guest

    By the things you have told, and assuming you don't have a carburation problem, you may also want check the spark plug "light" or "clearance" between electrodes (sorry I don't know the right word). A small "clearance" - this mean the electrodes are too close - can cause you a notorious limitation on the top end. I think 0.7mm it's a good value and works well in all my 4T or 2T bike engines, I use a hand saw blade as reference as it generally have this measure.
    By the way, you probably have to change the carb float. Once it's damaged I don't know if it could ever work properly again.
    Hope some of this works!
    Last edited by a moderator: Dec 17, 2015
  3. MotorMac

    MotorMac Member

    check this

    In the tank shutoff valve there is a small screen that you should check to see if its clogged, if it is then throw it away and get an inline filter.I know you probably already checked this but sometimes its the small simple things we overlook.Mac
  4. LabDude661

    LabDude661 New Member

    Well it turned out to probably be a simpler problem than I thought. I simply tightened the mounting points and the reduced vibration seems to have fixed the problem. I'm not sure how the vibration was hurting me but it's fixed now. Thanks for the suggestions.
  5. Mountainman

    Mountainman Active Member

    float filled with fuel

    even if this was not the problem -- some gas inside the float

    your float should be repaired -- solder or braze -- broken seam ?

    these floats leaking years ago was a VERY UNCOMMON PROBLEM
    but - seen way more often these days ????

    Ride That Thing Mountainman
  6. LabDude661

    LabDude661 New Member

    Yeah I fixed the float with some JB weld. I'm not really sure if it was a seam break or what but I haven't gotten anymore in there since I resealed it. It seems like a bad part of the carb to make cheaply. It's such a hassle to get the carb apart and empty the cup. I'm still not complaining. I'm rolling again and I learned yet another HT lesson.