Huasheng 4 stroke revs up and dies when choke is turned off

Discussion in '4-Stroke Engines' started by Maddmatt, Sep 28, 2008.

  1. Maddmatt

    Maddmatt New Member

    My 4 stroke Huasheng ran fine, but then sat for 3 months. I've stripped down the carb and cleaned every nook and cranny but it only idles with the choke on and the second i turn the choke off, it revs up and dies within seconds.

    It's driving me mad. I can't for the life of me figure out whats wrong.

    The spark plug is good and gapped correctly
    There are no air leaks between carb and engine
    Wires are all connected correctly (kill switch etc)
    New gasoline, 92 octane
    gas cap is vented correctly
    black hose from air intake is connected with the engine block
    Air/fuel screw is currently at 2 1/4 turns out
    New oil in sump

    If I leave the choke on it will idle for ever, the second I take it off it revs up, tries to take off and dies. WHY!?!?!!

    Help me.

  2. sparky

    sparky Active Member

    Sure you're not mistaking on and off?? Ya don't have 'em backwards, right?

    My carb says off when the choke is actually doing it's job of choking.
  3. skyl4rk

    skyl4rk Guest

    Change the fuel filter. Take the petcock assembly out of the tank and blow some air through it.
  4. Maddmatt

    Maddmatt New Member

    Already checked that.

    New fully functional petcock, clean, working.

    New fuel filter.

    Still doesn't work.
  5. HoughMade

    HoughMade Guest

    It's got all the signs of fuel starvation. Runs with choke on, but not when off.

    When you say it revs up when you turn the choke off, does it rev up like it is "running away" on its own, or does it just rev a bit and smooth like it should when the choke is turned off, or it it you revving it up after the choke is off?

    When you say you cleaned the carb, did you take the jet out, all the adjustment screws and needles and pry out the plastic plug under the plastic idle speed screw? In taking my Honda carb apart in the last week, I discovered a lot of additional nooks and crannies I never knew about before. Does the float seem like it is moving freely?

    Here is a link to a post that has good pics of the disassembled HS carb.
  6. Maddmatt

    Maddmatt New Member

    I took apart the entire carb. it was bare parts, I cleaned those bare parts, then re-assembled.

    Yes I understand the difference of on and off. I can see the choke doing it's job.
  7. Emmased

    Emmased New Member

    Mine behaved in much the same way. I removed the filter inside the tank and used just the aftermarket one I installed between the tank and the carb. Never had a problem since.
  8. H/S Carb blues?

    HI well I had a very similar problem with mine, after neglecting to drain the BAD CA. gas when the gearbox croaked.

    I cleaned and worked in that carb twice, unsucessfully, and have obtained a new replacement carb, so I can continue testing.

  9. POPS

    POPS Member

    H/S carb Blues

    Hi...Maybe try putting some clear line on from gas tank to carb so you can see whats going on??? Could also be the float level set too lean ( Not enough fuel in the bowl )??? Just some thoughts,Trying to help. POPS
  10. Maddmatt

    Maddmatt New Member

    Ok so I have an update.

    I ran the engine with the choke on, then sprayed an aerosol carb cleaner at the joints to see if I had a leaky gasket. In theory if anything is getting sucked through then i would hear it in the idle.

    It worked. I found my air leak.

    But it's not from a gasket. It's from the throttle arm. I'm familiar with this problem with VW carbs, once an old VW carb is taking in air from the throttle assembly it's done for. Time to buy a new one. Anyone know if this can be rebuilt? Should I just order a new carb?
  11. Irish John

    Irish John Guest

    If you haven't had the carb long they should replace it free of charge. I think most suppliers don't supply carbs and will try to sell you a new engine.
    I'm glad you found the problem cos I was about to say replace your kill switch with a Yamaha or Suzuki one (Aus$18.00) cos the grubee one is a piece of crud. If your engine ever splutters and loses power when underway you'll know it's the kill switch. You've been the victim of a severe Grubing and I'll bet a new carb is expensive if you can get a supplier to answer the phone cos they don't respond to emails.
  12. Maddmatt

    Maddmatt New Member

    I've had it for about 1 1/2 years, but it did sit with gas in it for 6 months. I found that many of the chinese o rings and other things of that nature are not resistant to gasoline like they should be. Crappy rubber hardens with extended exposure to gas, (grubee fuel line is a great example).

    As far as getting a new carb, it's cheap and easy but will just take a while. My father and I are just about to launch a bicycle engine supply website, our 40ft container arrives mid december. I'll have everything I need then.
  13. Irish John

    Irish John Guest

    That is fabbo Maddmatt. Good on you and your Dad. If you PM me your website or contact details I'll gladly buy parts from you and especially kits if they are better than the opposition. The competition you'll face is so laid back they're horizontal. I'd love a site with all the things for motored 4-stroke bikes like analogue speedos, freewheel sprockets, kill switches, 48T or 50T sprockets instead of the 56T which I now have 5 surplus of and, most importantly, the nice old 1 piece cranks and not those revolting 3 piece yokes with kiddy length cranks they are offering now. Keep me posted.
  14. HeadSmess

    HeadSmess Well-Known Member


    i read this and crossed my fingers and hoped it was the case...leaky throttle shaft.

    stripped carby(only ten times in two days!) removed rod, machined groove and inserted an o-ring.

    moral of the story? use the lathe to make an adaptor plate to take a z50 style slide carbie:thinking:

    ok, my problem.

    just put a huasheng onto my bike. went for the chain drive to rear sprocket style, after having tried FD too many times before with all those hassles... (a 5km hill in drizzle is almost reason to cry)

    so, chain, tensioner, frame, tank.

    tanks lower than carbie so i flogged a pump from an old briggsy. pressure pulse from rocker cover.

    all has been good for past two weeks. not.a.problem! beauuuutiful :)

    yesterday, ride to a friends, a fair trek. halfway, engine starts coughing, dies.


    pulse feed for the pump had some oil in the line. drained it. remove fuel line, crank engine. pumps working fine.

    attempt to start, nothing.

    go full choke, starts.

    choke off, dies.

    grrr, i say. ive had an issue with the carbie before with the engine on a stand. apparantly fixed.

    so, rode home, full choke, splutter splutter, not terribly great fuel economy on that trip...

    stripped carbie, cleaned thoroughly, every **** orifice, even using ultra fine wire to get into the two idle ports visible just as you crack the throttle. everything. compressed air, a soak in acetone, carbie cleaner, more probing with the wire, more air, ad nauseum. blindfolded, i could dismantle n reassemble one of these with my pinky toes now.

    it is not;

    fuel pump. float bowl is always full. problems still there when i use a normal gravity feed with no pump.

    dirty fuel. i siphoned some different brand petrol from the mothers van, and flushed system. no use. no water, no contamination, etc.

    plug. changed plug. twice.

    main jet. approx 0,8mm. every lil hole is clear, emulsion tube holes, blah blah.

    leaking gaskets. gasket goo, leak tests, you name it, ive tried it.

    the lil plastic cap under the idle screw, pulled that, replaced o-rings, they tend to get chewed. nope.

    valve clearance. gapped to 0.05.

    my pulse feed. i considered it might be the crank breather acting as a venturi the way its set up on the air cleaner, causing pump not to pump.

    blocked off my pulse feed. no difference. and it couldnt have been this anyway, as the pump is working...

    float height. fixed. un adjustable. plastic molding.

    nothing has worked.

    there is no killswitch or wires to be leading me off track.

    all else i can think of is my coil is starting to burn out, which would be annoying, but possibly not as annoying as not having any idea whatsoever!

    also have no coil to try. at least, one that matches the crank radius.

    its not a terribly complicated carby. so why the problems? grrrr.

    anyway. my few last tricks are to drill the jet(which i see as being sorta pointless cus its been fine up til now),replace carbie, or modify a brushcutter coil...


    any ideas ppl?

    it sounds like it is starving. and the earlier problem was when i blocked the overflow. that had much the same effect... it is not blocked this time!
  15. scotto-

    scotto- Member

    My first guess would be the pilot screw...supposed to be set at 1 1/8 turns out, not 2 1/4. This would be a simple fix!

    EDIT: This is in response to the original poster's question.
    Last edited: May 17, 2010
  16. sparky

    sparky Active Member

    My guess would be air.

    The carb's prolly not getting a good seal.

    Full choke starts it... slide the choke half-way down and see if she runs like a champ or not.
  17. HeadSmess

    HeadSmess Well-Known Member

    thanks for the reply.

    unfortunately. no. when it stuffed up it was full choke or nothing. tried. several times.

    now fitted a 20mm slide carby off a pit bike(50cc). didnt have much luck there, either. at first.

    a real head scratcher.

    changed the plug again, and wow. started with the new carb. full choke only.

    so richen the pilot and its running, no choke. very badly. jet sizes are way off. idle? what idle?

    so, thinking ok, maybe it was a faulty plug, followed by another faulty plug, i tried the original carb again, with the new plug.


    fixed? nope! if anything, worse :p so, yes. its carb related. not spark.

    some drilling of pilot jet and im sort of getting results with the new one. its accelerating, very very rich though(cant drill the main jet smaller, unfortunately)
    :poop: carbie. should find a mikuni/kehein...something tuneable. the needle and jets are all wrong on this one i have. (was never really great on the engine it came off)

    anyways, ive just ordered an alternative engine, the zbox, so the huashengs getting the shelving treatment now. first time an engine has beat me so thoroughly and so...inexplicably. im the one ppl come to for help normally!:eek:

    frustrating cus i actually rely on it where i live...and its not common enough to just swap and test parts when needed.:poop: maybe in a year ill come back to it...

    *some text missing in case of thread jacking *
    Last edited: May 20, 2010
  18. jason ivanoff

    jason ivanoff New Member

    make sure your fuel line is tight.happend to me