Steve Best
Well-Known Member
Hey Gino,
I've souped up my Grubee Skyhawk with enough power to see 44mph on a single speed. I have no doubt it would have broke 50mph with proper gearing. I also had a jackshaft kit on my 50cc bike working through a conventional 7 speed derailleur. Here are my impressions:
A properly ported and rechambered China Girl (PK80 or Grubee) will easily make more than enough power, especially with a tuned pipe (I have not even started with tuned pipes yet) to achieve 50mph with the right gearing.
The jackshaft plates, shafts and sprockets are all heavy steel. With the chains, I found the jackshaft kit added a lot of weight to the bike, more than 10 lbs, almost as much as the motor. I kept the sprockets in close so while I did widen the pedals slightly for mine, but I could have kept the original pedals if I really wanted.
I didn't like:
1) having to "kick-start" the bike, but got used to it.
2) the extra weight of the jackshaft kit,over 10 lbs.
3) extra complication and chains to set tensions on extra chains
I did like:
1) no pedal start-away on hills, just release the clutch in low gear
2) quiet cruise at low rpm
3) noticed an improvement in fuel economy
4) no hill too steep even with a stock 50cc
If the jackshaft kit plates were made of aluminum and shaft kept short and the sprockets lightened and drilled you might get the jackshaft kit down near 5 lbs. The kick-start will still be required
I am riding mostly street with my 50cc so I removed the jackshaft and am running single speed again. With a little porting and head work it does 30+mph with the 50cc and that is plenty fast on a light bike. I like that I can lift it over fences and carry it up stairs.
I've souped up my Grubee Skyhawk with enough power to see 44mph on a single speed. I have no doubt it would have broke 50mph with proper gearing. I also had a jackshaft kit on my 50cc bike working through a conventional 7 speed derailleur. Here are my impressions:
A properly ported and rechambered China Girl (PK80 or Grubee) will easily make more than enough power, especially with a tuned pipe (I have not even started with tuned pipes yet) to achieve 50mph with the right gearing.
The jackshaft plates, shafts and sprockets are all heavy steel. With the chains, I found the jackshaft kit added a lot of weight to the bike, more than 10 lbs, almost as much as the motor. I kept the sprockets in close so while I did widen the pedals slightly for mine, but I could have kept the original pedals if I really wanted.
I didn't like:
1) having to "kick-start" the bike, but got used to it.
2) the extra weight of the jackshaft kit,over 10 lbs.
3) extra complication and chains to set tensions on extra chains
I did like:
1) no pedal start-away on hills, just release the clutch in low gear
2) quiet cruise at low rpm
3) noticed an improvement in fuel economy
4) no hill too steep even with a stock 50cc
If the jackshaft kit plates were made of aluminum and shaft kept short and the sprockets lightened and drilled you might get the jackshaft kit down near 5 lbs. The kick-start will still be required
I am riding mostly street with my 50cc so I removed the jackshaft and am running single speed again. With a little porting and head work it does 30+mph with the 50cc and that is plenty fast on a light bike. I like that I can lift it over fences and carry it up stairs.
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