Engine revving on high, throttle handle twists very little

Discussion in '2-Stroke Engines' started by asfazrq, May 31, 2010.

  1. asfazrq

    asfazrq Member

    The issue is that engine is revvs super high on idle. I recently changed from a 44T stock sprocket to a 36T rear sprocket and immdiately the engine revved extremely high. I have played with a idle screw twisted it all the way in and the 3.5 turns outwards but that has done nothing. I checked the carburetor and ensured that the brass barrel is properly seated. along the way the throttle handle would not pull so I changed the throttle cable. the little screw (horizontal one) on top of the carb cover is screwed all the way down, lowest cable tension but still that does not cut it. top speed is 33 mph and the idle speed without touching the throttle goes up to 26mph. I have done everyhing I can, made sure there are no kinks or sharp bends in the throttle cable, but to no avail. Initially the throttle handle used to twist quite a bit but now it turns around half than it used to.

    I am not sure if the throttle handle is already pulling it a bit at the rest position. I had huge issues connecting the throttle cable to the little hole in the throttle handle. after connecting th cable and then screwing the the handle to the kill switch assembly the throttle handle would not turn, but the groove in which the throttle cable goes goes stuck in the groove in the kill switch where the throttle cable passes. not sure if I am describing it properly. but it was pain to even get so far - I had to slightly twist the trottle and then close the screws on the kill switch assmebly. that was unfortunately the only way the throttle would twist.

    need your help and kind advise. very much appreciated.

  2. core2kid

    core2kid Member

    Mine did this today. What I had to do was loosen the screw holding the cable by the throttle and where the cable goes into the carb. Loosen it all the way and you should see a lot of slack. You could even take apart the throttle and let the cable loose. Then tighten your idle screw all the way, start it and start unscrewing the idle screw. It should lower in idle speed.
  3. asfazrq

    asfazrq Member

    I have already done that, both the ends of the throttle cable are set to loose - the end that connections to the kill switch and one that connects to the carb, still nothing.
  4. Al.Fisherman

    Al.Fisherman Active Member

    Check for a intake leak.
  5. asfazrq

    asfazrq Member

    I added a boost bottle kit (useless thing) with a pre-drilled manifold (has teflon tape on the drill screw so should be airtight). i had to replace the old (non-drilled) intake manifold and it's gasket was completed super glued to it so I made my own gasket with a very think cardboard. I kept the cardboard to be slightly larger than the original gasket and made sure that hole was exactly the size as the intake manifold opening. it's a thick cardboard a few times thicker than the original gasket. could that be the culprit?
  6. motorpsycho

    motorpsycho Active Member

    a cardboard intake gasket? ummm, yeah, pretty much the same as having no gasket at all...probably has a major air leak.
    since the engine is revving really high, are you positive that the slide in the carb. is not stuck wide open?
  7. AussieSteve

    AussieSteve Active Member

    If you remove the air filter, you might be able to see into the carb's inlet to see if the slide is right down. I'd do this with the idle screw loosened right off.
    Otherwise, you could remove the carb with the throttle cable still connected and really see what's going on.
    As motorpsycho says, it does sound like the slide is staying partly or fully open.

    Even if that is the case, it would still be a good idea to replace that gasket with a decent one. You can buy them cheaply, or you could buy some 'oil jointing paper' and make your own. I use 0.8mm, but I carefully flat-filed both surfaces first, with the studs removed from the cylinder. Use thicker if you can get it.

    If the slide is returning right to the bottom then, as Ron said, you most likely have an air leak. A really bad one.

    If the boost bottle is useless, while you're at it you could p iss it off and fit the stock inlet.

    Best way to check if there's a problem with the twist-grip is to disconnect the cable from the carb then see if you're getting full travel.

    Also, I see that at the bottom of this page under 'Similar Threads' there are two that appear related. (Haven't read them myself.) Might be worth a look, but the advice will probably be the same as ours'.
    Last edited: Jun 1, 2010
  8. asfazrq

    asfazrq Member

    I have a feeling it won't be all the way down. I think the issue is with the throttle cable connecting to the throttle handle. It most probably is pulling the throttle cable half way through (or possiblly more) at the rest position. I pointed out in my original post that the throttle handle doesn't turn much - which leads me to believe that the cable is not setup properly in the throttle handle! what is the correct method to setup the throttle cable in the handle? coz I tell you what, I have to partially turn the throttle handle while screwing in the handle to the kill switch assmebly housing. i had no choice, b/c at the 100% rest position it will not turn after closing the kill switch housing. please advise
  9. AussieSteve

    AussieSteve Active Member

    I have to turn mine a little, after attaching the cable, before the cover will screw on properly. Not much, though.

    I just went back and re-read your first post for clues. You mentioned that you changed the throttle cable. Is the cable and the outer casing the same length as the original cable? It sounds like you've got a shorter cable or longer outer casing.

    Another point, you said 'I have a feeling it won't be all the way down'.
    You're probably right, but it's better to have a look than it is to have a feeling. Then we'll be sure where we stand.
    Last edited: Jun 1, 2010
  10. asfazrq

    asfazrq Member

    if the outer casing is longer, how do I fix it?
  11. motorpsycho

    motorpsycho Active Member

    if the outer casing of your throttle cable is longer than the actual cable, something is wrong. all throttle cables are made so that the inner cable is always longer than the outer casing. the ends of the actual cable will peices soldered or crimped on them to seat in the throttle handle housing, and in the carb. slide.
    if the outer casing is longer than the actual cable, there is no way that they could have crimped or soldered the ends onto the cable.
    are you sure that you got the right cable? it almost sounds like it might be broken.
    Last edited: Jun 1, 2010
  12. AussieSteve

    AussieSteve Active Member

    I didn't mean that the outer cable night be longer than the inner casing. Of course, then, there wouldn't be a nipple at each end.
    I meant that it might be the wrong cable.

    asfazrq, compare the new one with the old one and check that both have the same amount of cable free of the casing and that the nipples, especially at the twist-grip end, are the same as the original.

    Brake, gear and clutch cables can easily be shortened, (either the casing or the cable), because they only have a nipple at one end. Throttle cables have nipples at both ends and so can't be shortened without soldering or brazing a new nipple on afterwards.
    I cut my over-long clutch cable and gear cable to length to suit the bike.
  13. asfazrq

    asfazrq Member

    I ended up taking the little screw on top of the carb cap, which allowed me to the lower the brass barrel at the lowest position. this ended up in the engine revving less at idle, so I figured what the issue was. the bad news is that i lost like 3mph on the top end b/c the brass barrel only goes this much high when the throttle is pulled to the max. I figured, i'd rather shut off the engine at idle than lose the top end! any concerns with doing that? please advise.
  14. AussieSteve

    AussieSteve Active Member

    Despite my asking, you didn't mention if the cable travel is shorter than the original. I guess it is, by the sound of things.
    (Makes it hard to diagnose without the full story.)

    The cable shouldn't affect the idle at all. To raise the idle, screw in the idle speed screw on the LHS of the carby.

    Still, personally, I wouldn't accept the situation. I'd replace the cable with the correct one so that I could get full throttle. Removing the cable adjuster from the top of the carb is a crude fix.

    Did you replace the intake gasket to ensure it's not leaking as well?
    Last edited: Jun 7, 2010
  15. motorpsycho

    motorpsycho Active Member

    it still sounds to me like the cable is way too short, which is not letting the slide bottom out in the carb.
    you need to get the correct cable, and it will be the correct length.
    it will allow your engine to idle AND give you full throttle.
    you should have full control of the throttle...you should never let the engine just rev like crazy on it's own. you need to be able to adjust the idle by turning the idle screw, never by shortening or lengthening the cable.
    your "fix" isn't a fix at all, it's just rigged up to make it work somewhat.
    you need to fix it right.
  16. asfazrq

    asfazrq Member

    guys you're super awesome. i crashed because of road construction the other day, hurt myself pretty bad but I survived and my craze for MB has only increased. i have ordered some new parts e.g. centrigufal clutch so gotta do some repairs to the bike before I tinker with it more. all of a sudden the engine idles at acceptable revving, but with the clutch semi-broken it's difficult to tell if I actually fixed it. i'll do the repairs and will keep you posted. just haven't had a chance to compare the cable. thanks for helping out and the reminders.