Cannot get HT to fire up

Discussion in '2-Stroke Engines' started by Irish John, Apr 14, 2009.

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  1. Irish John

    Irish John Guest

    I'm trying to fix a near new 48cc HT which stopped firing before I tried to help the guy who owns it.
    I've replaced the magneto & coil and the CDI.
    I wired it up blue magneto to blue CDI & ditto for black then killswitch yellow stripe to black & then kill switch green to blue. That is all OK and I can see a spark from the plug but it might be a weak spark I don't know.
    I've put a good NGK 6BHS plug in which is usually the best plug.
    Cleaned the carby completely but still no firing up of engine.
    Could it be the kill switch itself?
    I adjusted the clutch so it bites really hard and should improve the spark.
    I notice that the gasket on the inlet manifold is 10 times thinner than it used to be so not sure if air is getting in there. The thin gasket is just more quality fade since I last dirtied my hands on an HT 3 months ago. I've checked head bolts and exhaust bolts and inlet manifold bolts.
    I don't think it is fuel problem but I'll replace the cock next.
    Has anyone got any idea why this little beast wont fire up even on 400 metre hill. It fires but won't accellerate or stay firing if I pul the clutch in.
    Last edited by a moderator: Apr 14, 2009

  2. BoltsMissing

    BoltsMissing Active Member

    test it again with no switches connected, straight blue to blue, black to black.

    Regarding carby and exhaust gaskets, make the same shape as port holes.

    Seal up the carby inlet part where it slides into the manifold with level pink plumbers thread tape. I usually remove the clamp, wind some tape so it covers the slots in carby and then slide the clamp over the thread tape, and wind some on manifold. It Seals it good.

    NGK plug, NGK Plug Cap and use a differant copper lead, the kit's copper lead is not the right type. The copper is too thin as compared to aussie made copper plug leads from auto electricians.
  3. machiasmort

    machiasmort Active Member

    Did you get that thing runnin?
  4. 247Jude

    247Jude Member

    I had a simular problem, it was the spark plug, the gap was briged by a small piece of metel. It looked like a small ball bearing.
  5. Irish John

    Irish John Guest

    You mean disconnect the kill switch wires completely to diagnose if it's the kill switch. GOOD THINKING BOLTS WILL DO TOMORROW FIRST THING

    I don't think this is necessary Bolts - too time consuming & almost certain its not the probleem. I could use gaket mastic compound stuff instead. Last option.

    That's been done at the outset but I could try yet another carby - would be third carby tried

    The plug & lead is part of the CDI I can't just pull it off and glue another one on to the CDI. This can't be the problem. I've had faulty CDIs before but not twice in succession that's too unlikely even by HT standards
    This is the second CDI and lead/plug and it's a new replacement from ZBox as is the Magneto and coil. I put the magneto on carefully using a spacer between magnet and whatsit.

    I think the first option might get me somewhere cos I haven't eliminated the kill switch yet and they are the cruddyest components in any HT kit. If it isn't the kill switch it has to be the fuel line or carby.
    There is no firing up yet the plug sparks. Hoiw can that happen. It's a good plug - all my plugs are good & I have dozens of them.

    WHAT ELSE CAN IT BE??? I reckon it must be the kill switch cos of all HT components my opinion of the kill switch is the lowest. Lower than whale excrement!!
    Last edited by a moderator: Apr 14, 2009
  6. Irish John

    Irish John Guest

    I'm using plugs that work on other HT motors mostly NGK 6BL Hs I think they are and they are usually the best. I have dozens of working plugs off other HTs. That ball bearing was probaly put in your plug gap by a disaffected worker who resented being herded into the factory at gunpoint every morning at 3AM. How else would it have got there seriously Jude?
  7. 247Jude

    247Jude Member

    It was formed by the seating of the rings. It was runing fine and one time it stopped! I thought it was the cdi or magneto! But that little ball of metel was what I found! After changing the magneto.
  8. 247Jude

    247Jude Member

    I use platium 4 plugs now.
  9. BoltsMissing

    BoltsMissing Active Member

    There is a wood screw looking thing in the CDI where the lead fits, so you have to unscrew the lead. perhaps there is a bit of moisture, who knows.

    Yes. And if it works, no need to fix the kit's kill switch, the extensive length of wiring seem to tax a bit of it's potentially high performance. I use a On/Off toggle at the least as close as to the CDI as possible to keep the wiring as short as possible.
    Had no switch once but it seems to make some purists react, so I now use a switch. But for testing and process of elimination purposes to find fault, no need for a switch for now.

    Ok, but I found the best approach is the, "leave no stones unturned" method, just in case.

    Remove the fuel tap and remove the kit's filter, add a in-line filter.

    The kit's filter may have a tendency to restrict fuel flow.

    Since reading somewhere once where a HT spark plug lost it's tip inside a new engine, then that get's thrown out to and replace with NGK B6HS, gap at .025 and ought to get the basics out the way.
  10. Irish John

    Irish John Guest

    Thanks a lot Bolts - your perfectionism is worse than my own - you really have given me great advice covering every conceivable angle and I'll be onto it in the morning.
    I'll bet you a schooner of 20:1 best 2-stroke mixture that it's the kill switch. I am seldom disappointed at my propensity for being wrong about these things so I look forward to losing. I've never found it this hard to get the HT to run.
    A midi of best 2-stroke mixture says it's the Carby!
    Last edited by a moderator: Apr 14, 2009
  11. 247Jude

    247Jude Member

    Check your cab for any cracks or fractures. The same for the intake manifold, and gaskets on the intake side. Air filter? It runs but not well?
  12. arceeguy

    arceeguy Active Member

    Just a long shot:

    Check to see that the woodruff key is installed on the magnet. If the magnet isn't aligned properly, timing will be off. Might explain the spark but no "bang".
  13. one time mine wouldnt start,i had the gas petcock turned off.
  14. ozzmonaut

    ozzmonaut New Member

    I'm gonna go with killswitch. I had the same problem with my weedeater friction drive. I wasn't even sure it was the killswitch but it was a beefy switch from the 60's so I hit it real hard a couple times with a wrench and it worked. But then it happened a few times after that so I replaced it with a switch off of some old fox-frame mini bike and that is what is still there.
  15. Irish John

    Irish John Guest

    It's NOT the kill switch

    I disconnected the kill switch and the motor still won't fire up except sort of on steep downhills. No difference.
    I need to assume that the turkey who owns this might have the wrong fuel in the tank.
    I will refuel the whole shebang and try that before I try replacing the carby again which I'm fairly certain is OK.
    The wires are new and look quite OK - no cracked insulating etc.
    The bike looks like it's been ridden on dirt roads or the beach. The former is just stupid and the letter is insane.
    I cannot be defeated by a substandard Chinese pice of ***t.
    I must win this battle for the honour of my name!
  16. BoltsMissing

    BoltsMissing Active Member

    Na, bets are off for me Irish, 100/1 "Murphy's law" in the field on these HT's
    But the form of things seems the switch is more than likely to be the run home.
  17. Irish John

    Irish John Guest

    Sorry Bolts but you called off the bet too late and there's a dozen schooners of finest two-stroke mixture with your name written on them waiting for you at the Billinudgel Hotel. Just tell the guy Brad your name is Bolts and he'll start pouring.
    It can't be the kill switch. Before I try your other treatments I think I should treat the fuel as tainted and refuel the bike cos I didn't put the fuel in there.
    If it is the fuel I am going to have to tell the guy I'm doing this favour for that he's an idiot.
    Well back out there to try and solve this. Thanks guys for your help & I hope we succeed.
  18. arceeguy

    arceeguy Active Member

    Looks like the score is:

    Piece of sh1t - 1
    Irish John - 0

    Last edited: Apr 14, 2009
  19. 247Jude

    247Jude Member

    Lol well is there anything you haven't changed, how is the compresion? In other words have you changed the rings?
  20. arceeguy

    arceeguy Active Member

    It's a two stoke engine - one of the simplest pieces of machinery.

    Got air

    Got fuel

    Got spark

    Still thinking something is up with that magnet.


    If you have an inductive timimg light handy, make some timing marks on the magnet at TDC, remove the plug (to relieve compression) and roll the bike forward and see if the ignition timing is close. Might need two people to do this. One to roll the bike, the other to aim the timing light.