Engine Trouble Won't rev high enough?

Discussion in '2-Stroke Engines' started by p4cm4n, Jun 14, 2016.

  1. p4cm4n

    p4cm4n New Member

    so a few weeks ago I put together my build from some years ago.

    Many thanks to SBP, specifically Jim for all his help. He personally emailed me with answers to all my dumb questions.

    Now I think I have some engine problems.

    My mixture is 40:1. My idle is what I consider perfect. My plug is a pretty close to perfect if not perfect color, after much fidgeting. My engine is a 66cc on a cruiser bike, 7 speed with a SBP shift kit. Now that I've adjusted and perfected things like my rear dérailleur and brakes and started moving, I can't get a decent speed.

    I'm 230lbs give or take, I haven't been hauling a load behind me. Going from gear 1 on the bike, (don't have tooth specs with me now, can get them later) I hover about 18 miles an hour. Going up each individual gear, I only gain about 1-1.5 miles per hour, occasionally 2. By 7th gear, I top out at 29.

    If I don't sit on the bike, prop it up, and use WOT to spin the tire, you can really feel that two stroke vibration on my pre-balanced crank. But while on it, very comfortable ride...no vibration really considering..just can't get any speed or anything.

    Any ideas of things to look at?

  2. p4cm4n

    p4cm4n New Member

    Oh yeah, to throw it in there, it's a b6hs plug with 93 octane fuel, gumout brand (sheetz) oil, a 2011 skyhawk, and the standard setup from SBP sprocket wise
  3. jaguar

    jaguar Well-Known Member

    Have you
    -replaced that shitty stock air filter?
    -used sandpaper on glass to plane flat your cylinder head to prevent power robbing leaks? (you can also use this method to increase cylinder compression which is a sure fire way of getting more power output. Just start out with a really rough sandpaper to take off a half millimeter from the mating surface.)
    -put an iridium plug on it?
    -used a rotary tool to increase intake port duration by raising the skirt?
    -cleaned the contact area for the stator coils mounting screws which are the ground path for the spark? resistance there reduces spark power which reduces engine power.
  4. crassius

    crassius Well-Known Member

    at 230lb, that's all some folks get

    with shift kit, many folks see a loss of speed due to extra turning weight in gear system

    if the problem is elsewhere, think in these terms: if motor seems not to rev as high as you'd expect, then your high gear may be too high, try a smaller pedal crank gear - otherwise if engine is reving high enough, you may need a larger pedal crank gear
  5. Thanks

    Thanks Guest

    jaguar :

    You may have been one of the replies on a previous thread for me - specifically that I cannot get the body of the engine apart. I can get the top of the head off, that is all. Not the cylinder body. I have not done any shaving of size there, however it is flat (I have checked). I may do this.

    The plug is a NGK b5 or b6hs. I think I have both. Haven't tried iridium. I'm going to do a plug chop today most likely and will try to get an iridium to replace after.

    Haven't done anything with the skirt as I can't get inside the body safely.

    The contact area for the stator is mostly clean, some of the magnet looks rusty though. Could this affect it? I tried to get a new coil but couldn't install for some reason as the wholes lined up in a slightly misaligned fashion which concerned me for clearance on all sides.

    And thanks crassius seems I may be too fat I rode this a few years ago when I was about 180-190 and got a fair bit of speed out of it on the standard 44 tooth sprocket. Hoped the shift kit would extend that. Oh well.
  6. Thanks

    Thanks Guest

    oh and I have a brand new dellorto clone with low profile air filter.