Motor Kit Advice?

Discussion in 'General Questions' started by Tressie, Apr 5, 2013.

  1. Tressie

    Tressie Member


    I've been looking at a cheapy 49cc Chinese conversion kit on eBay:

    My local legislative requirement is for a maximum power of 200W, so I figure the 49cc should be quite adequate in a detuned or RPM limited configuration. I've done the measurements and calculations and know that 200W affords me a 21.5km/h top speed, so that shouldn't be too hard to invoke.

    My questions relate to the various versions of these motor kits available, as well as to the operation of any governing mechanism, and additionally the specific CDI unit functioning. Basically, am I looking at the right kit with no obvious known issues, or is there a better choice that I don't yet know about.

    Secondly the governor. Does it have one, and if so can it be accurately set for any particular maximum RPM?

    Failing the availability of a workable governor, I'm then curious about the individual funtions of the 2 thin electrical wires leading to the CDI ignition unit. It seems this might be a point at which RPM might be measured, and ignition interrupted by a simple microcontroller unit in the case of an over-rev condition.

    Thoughts anyone?

    Thanks for reading,

    T :cool:

  2. Anton

    Anton Administrator Staff Member

    Hey welcome. The engine in the link is a Chinese HT "Happy Times" engine. These are the most commonly used 2 stroke bike engines.

    Ok by governor you mean speed limitation. There's nothing on these engine's to limit the speed. They are a lot more than 200W out of the box too.

    Here's a good discussion about the motorized bike laws in australia:
  3. Tressie

    Tressie Member

    Hi Anton,

    Thanks for the warm welcome, and especially for visiting the link and identifying the "Happy Times" motor kit I had mentioned. No red flags with this choice by the sounds of it.

    The link you posted, concerning Australian motorised bicycle laws and policing practices, was something of a shock. I anticipated that I could expect to be pulled over and questioned regarding regulatory compliance, but by the sounds of it I might be in for something of a lost battle. I guess you prepare for the worst (compliance documentation), hope for the best, and then see how it all plays out in the court system.

    One thing that had become evident, whilst I read of unhappy encounters with authorities, was this: If someone is actually going to dyno a bicycle suspected of non conformity, then merely restricting RPM as a power limiting measure isn't going to fly. A better solution might then be to install a constriction in line with induction plumbing, not unlike is done in some classes of competitive motorsport. The disadvantage with such a scheme, however, is that a 2-stroke engine so de-tuned will provide insignificant output at lower speeds and RPM. I might get my 21.5km/h top speed with the 200W, but getting there is going to take additional pedalling every time, or otherwise a v-e-r-y long time. This is where 200W electric motors have the unfair advantage, as they develop torque right from the start. Bother! WA legislation talks of a top speed of 25km/h being the objective of the power limit, so one wonders whether a speed limit, as opposed to a power limit, wouldn't have been a saner governing implement (?).

    Okay, any extra tips, to help a 2-stroke newbie get the best out of his intended "Happy Times" acquisition, would be especially welcome at this point.

    Hope I haven't prattled alone too much. Happy cycling everyone!

    T :grin5:
  4. Anton

    Anton Administrator Staff Member

    Actually I just had another look and this is a really cheap HT engine. The quality of the engine may be pretty poor if it's anything like the ones from this ebay seller

    There are a couple of other options:
    Zbox -
    Rock Solid Engines -

    The engines these guys sell are a lot more expensive than the ebay engines. They look similar but I think each factory has different quality assurance measures in place. I have engines from both Zbox and Rock Solid engines and they are fine. I can't comment on the ebay kit you pointed out since I have never tried it out. I guess it's all down to how much you are planning to ride the bike. There's plenty of ideas on the forum about how to make your kit reliable.

    As for the aus laws keep looking through for more ideas. I think the main thing is to obey all the road rules.
  5. Tressie

    Tressie Member

    Slant head or symetrical?


    It seems that locally I may have the choice of 2-types of 49cc "Happy Times" engine kits. One engine has the spark plug set at an angle to the plane of the head, and the other has the spark perpendicular to it.

    Can anyone please tell me what may be the difference in these variants, and whether one style might be preferrable to the other?

    Thanks for any thoughts,

    T. :confused:
  6. Anton

    Anton Administrator Staff Member

  7. darwin

    darwin Well-Known Member

    With the laws so restrictive in cc size/200wts how do you guys stay legal down under?
  8. Tressie

    Tressie Member

    Haha, that's a funny thread. Thanks, Anton.

    Hmm...maybe I should take a closer look at the bike I'll be using, currently at my sisters place in the country, to afford myself the best chance of sourcing the style of engine that will fit it's frame correctly.

    T. :rolleyes7:
  9. Tressie

    Tressie Member

    Silver or Black?

    Okay, it sounds like the non-slanted, or 'Hemi', head might be preferrable, should it fit. Now what about the motor colour?

    I know that the thermal emissivity of silvery looking metals can be quite low, resulting in poor heat dissipation and substantially inaccurate non-contact thermometer readings. Would I be correct in assuming that the black anodised finish available on some HT engines, will help them to radiate heat more efficiently, and therefore to run cooler? That's a good thing for an air cooled 2-stroke, isn't it?

    T. :confused:
  10. crassius

    crassius Well-Known Member

    I like the look of the black engines, but the bare metal ones are easier to spot leaks on before they become a problem. Any color but bare metal is often due to a cheap paint job which may affect cooling a bit.
  11. Tressie

    Tressie Member

    Stud replacement?

    I read somewhere that the studs for the head, intake and exhaust are pretty poor spec, and should be replaced first thing.

    If I cut-up some high tensile strength steel bolts to fit, then what should I use to glue them into the cylinder? I hear Loctite won't handle the temperature.

    T. :whistling:
  12. jaguar

    jaguar Well-Known Member

    the temp isn't too high for Loctite.
    as far as rpm limiting, 2 strokes limit the rpm by the height of the exhaust port. too complicated to fully explain here. click on my signature link and lick on the link for "porting for peak rpm". the authorities go mostly by engine size and top mph (or kph in your case). These engines aren't marked as to their size. They won't put your bike on a dyno to check for how much horsepower it has. So you can increase the power w/o increasing the maximum speed.

    Yes, if you don't correct engine vibration you will need stronger nuts/bolts and Loctite. Also you'll need to replace the upper conrod bearing after a year since the extra compression psi caused by too advanced ignition at top rpm will destroy the stock bearing. the replacement bearings are better.
  13. Tressie

    Tressie Member

    Hi Michael,

    Ah, thats the sort of info I had been hoping for. You've obviously gotten right into 2-stroke engines, so I suspect you're the man to ask.

    Okay, if you we going to de-tune a 48cc HT in order to limit it's output to around 200W, then how would you tackle the operation? On the one hand, there's a (pricey) commercial kit that comprises of 'matched' air filter, intake port and exhaust port constrictions, along with unknown carburettor adjustments for smoother bottom end. Now having taken a brief look at the resources you had suggested, it appears a more favourable result might be obtained by way of exhaust port modification.

    T. :confused:
  14. Samdallas214

    Samdallas214 Member

    if there is any way you can afford it go American made the kits cost far more but are far better kits.

    I see you are on ebay just stay away from eBays boygofast he sells junk beware spend a little extra and go with a different seller even if you get it off eBay
  15. jaguar

    jaguar Well-Known Member

    JNMotors is preparing to sell improved engines but really if you take my advice and do it yourself you will have more pride in your machine as well as having increased your experiential knowledge.
    I don't think they need to be detuned. they already are. that's how they pass all govt regulations. they wont/cant know the actual power output so they just go by engine size (which they wont measure to verify) and top mph. So I say make it more powerful but dont raise the exhaust port so much that you can exceed the speed limit for them.
    Last edited: Apr 13, 2013
  16. Samdallas214

    Samdallas214 Member