china bike 122cc dohc 4 valve project

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Dialing cams tonight, what a crap job. Engine should start tomorrow night or the day after. Yey!
 

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Its Alive!!!

Woohoo! It runs! :D I haven't ridden it yet but it sounds f**king fat. The tune is wrong and the float is jammed so fuel is pouring out. I haven't finished putting the bike together either but its looking good at this stage. I'm quite excited about the prospect of revving the crap out of it hehehehe.
 
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Yeah you're probably right. Its only gonna be in the xr long enough to get the tune right and make sure its all happy. Then it gets loaded into my road registered z50j.
 

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tormentandglory said:
Yeah you're probably right. Its only gonna be in the xr long enough to get the tune right and make sure its all happy. Then it gets loaded into my road registered z50j.
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..lol:D :D ....but this buttugly ignitioncover has to go;)
 
hi mate whats going on with your motor??? can we see and here it run please you have got people all over the world watching this thread ( im from jersey channel islands ) it looks great a job well done
 
I'll try and get some video this afternoon. I'm having a bit of trouble with it. It doesn't seem to want to rev out properly. Runs smooth and strong in the lower revs but starts to complain when you give it a hard time. I've been fiddling with tune and tried 2 completely different ignition systems but that hasn't fixed it. I'm a bit puzzled actually... I think I need to get a different brain to have a look at it for some fresh ideas. I'm gonna buy a timing light and some sort of tacho for it today to. I put brass oil lines on it last weekend.
 

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Hmmm, I thought it wasn't revving up hard, but I was wrong. I bought an old gsxr750 tacho today and it seems that the engine spins up to about 11,500rpm. On the road, it only does about 65km/h (with my gps in my pocket). It's gonna need a final drive ratio of about 16/26 to get anywhere near 100km/h. The primary ratio inside the engine is way to low. I'm not sure if a 26 tooth rear sprocket will even fit on the hub! Does anyone know if there are different primary gear sets available for the china bikes?
There are 2 different gears sets for the honda engines. Points ignition honda 50's have a taller primary than the newer cdi type engines. Big wheel 70cc honda bikes (dax, sl70, etc...) run the shorter ratio, like the more modern 50cc bikes. My z50j does 75km/h with 16/35 gearing and it barely pulls 10,000rpm of the 88cc engine.

Check out the link, its a vid of the tacho. YouTube - twincam engine running with a gsxr750 tacho fitted
 
Takegawa 5gearbox...the fith is veeeeeery long...but it cost an arm and a leg and doesn't hold up long!
 
no_crf50_here said:
pitty your not closer, have a few 3v motors laying around....no idea what they are running gears wise tho...
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If you have one in pieces, and if its not to much trouble, could you count the teeth on the primary gears and let me know what they are please? That'll save me the trouble of pulling mine apart :)
 
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