Wasted a day tuning a 48 HT

Discussion in '2-Stroke Engines' started by Wildturkey, Apr 8, 2011.

  1. Wildturkey

    Wildturkey New Member

    I have always been lucky with my 70cc engine I guess. I spent the most part of today attempting to get a 48 to run well for a friend.

    I have 2 here a Rock Solid with 1000kms and a leaking crank seal, and a Zbox that is about 1 hour old. As I have many carbys and plugs here I have been trying all combinations with no luck. I have tried jet swapping, mixture settings, swapped plugs and plug gaps. I just can't get these things to sing. The plug always reads OK but never any 2 stroke action, and never any bottom end power. At times I can get it to scream up high. Though I then turn around to go back home and it won't do it again? They start very easy and will idle.

    The only thing I have not changed is the coil and plug leed? Could this be something to check out?

    I am a mechanic by trade and can tweek most things. But these have me stumped?

    Any clues????

  2. HeadSmess

    HeadSmess Well-Known Member

    YEP :) GIVE UP :)

    OOPS... capslock :eek:

    i went fourstroke so the ht has been surplus...i tried starting it the other day...i say TRIED....

    ill stick with my fourbangers now :) something about knowing theyll actually get you there and back...without carrying a full toolkit(usually!)

    yeah, ok, doesnt help...

    what can i say? can get one to scream one minute, the next your wondering why your pushing a motorised bike up a hill, when it doesnt have a flat tyre,nor is it out of fuel... conquer that hill, and it will haul up the next one, even steeper, without even slowing down... temperamental POS! :D
    Last edited: Apr 8, 2011
  3. Wildturkey

    Wildturkey New Member

    They are great when they are running. I hammered my last 70 off road MX style for over 5000Ks rarely let me down. When it did it usually had something to do with me.
  4. motorpsycho

    motorpsycho Active Member

    check for an air leak at the carb, or at the intake tube.
    try starting it with the choke on or your hand over the carb throat and see what happens.
  5. Wildturkey

    Wildturkey New Member

    Tried all that Psyco. It idles well.????
  6. HeadSmess

    HeadSmess Well-Known Member

    ok j, now its getting painful...

    exhaust? what type? standard? saying they sing is like saying my dog has perfect pitch when it howls...i wish! get an expansion chamber :) could even just want a cleanout...

    erm. leaks around the exhaust gasket can cause issues. youre rejetting, so id hope you know what youre doing (what? no computer? nope, cant service it!)

    theres still one...two...three. three different mixture settings on these. jet size, needle size and position, and the slide bevel. all working together for ideal transition... oh, and the oil/fuel ratio plays a part!

    anyways, getting in further... check crank seals, both sides...once they start going...bye bye! id peek at the engine that ran the longest...

    oh. it is the one losing the crank seal...oops!
    Last edited: Apr 9, 2011
  7. Wildturkey

    Wildturkey New Member

    Will do some more testing with a mate today.
    A fresh set of eyes may do some good?
  8. motorpsycho

    motorpsycho Active Member

    so did this help the problem or just make it stay the same?
  9. Wildturkey

    Wildturkey New Member

    We rode allday instead of work on junk.
  10. Biker

    Biker New Member

  11. Wildturkey

    Wildturkey New Member

    I tried something similar.

    I filed 1mm off the jet holder. This brings the jet closer to the needle.

    Slight improvement but I still get the feeling I am barking up the wrong tree.

    I will change the electricals today.

    As an apprentice mechanic 20 years ago. I remember a car pulling up to the workshop. Chugging and blowing richness smoke. Well all agreed it was running rich before the customer had got out the car. We were all wrong. Turns out the condensor inside the dizzy was faulty. Looked in every way to be running rich.
    Only ever seen this that once.

    I know, I know before somebody says something. Cars are 4 stroke. It is just a good demonstration that you need to keep an open mind.
  12. GearNut

    GearNut Active Member

    Hmmm... If you filed 1 mm off of the jet end of the jet holder it really won't make much of a difference. The needle and jet interact with each other on the other end of the jet holder (it's actually called a needle jet), the end that is visible when looking down the throat if the carburetor.