Boost porting the 68cc china engine

Some pictures of summerland 10 miles north of us taken on Sunday feb8
Youd think i work for the city -not sure how this relates to boost porting
lol.cargo
 

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Robin, I looked up beautiful places in the dictionary, and would you know it had the same pictures that you took. Wow, I am jealous. Have fun, Dave

PS: If our new president messes our place up like I think he is, I now know where to go.
 
I have been having carburetor issues and a new china carburetor is on its way but when the darn thing isn't runin so rich, I can pull some high rpm
 
Hey Robin, fellow Canadian, you live in one fo the most beautiful places in BC speaking from personal experiences only. always thought I would retire there. Problem is I can't take the heat. Hopefully I'll take a trip up there one June or September and ride the bike around.
 
Re: Boost porting the 67cc china engine

europorsche914 said:
Here is the mod that i did to my motor. I attempted to balance the crank while it was apart and stupid me didnt look up any info on it... So it now vibrates like all **** at 25mph. I didnt half the weight of the reciprocating assy. But not all was lost... Before the crankshaft and boost port mod i could at most do 34mph according to my speedometer. Now the same speedometer read 43mph! Now im not going to tell everyone that it is dead accurate since i do not have a gps to test it but i know im going approx 40 mph since i was keeping up with traffic... The crankshaft can only be holding the engine back and the sound of the motor at that rpm is very smooth. Current mods to my engine include porting intake and exhaust, expansion chamber, homemade glass pack and steel pack muffler, 44 tooth sprocket, NGK b5hs, polish the head and piston top, and 2 boost ports. The two ports were about 1/4" wide and are as long as the ceiling of the transfer ports. They are about 3/64" deep and are centered between the intake and transfer ports. The end of each port is angled towards the intake port and utilizes a steep angle to aim at the sparkplug and help scavenge the exhaust charge out of the cylinder. Im satisfied with this mod and would do it again but will be tearing the motor down again to install a new balanced crankshaft... Please excuse the poor grinding on the one port, they ran out of grinding stones at the store and i will clean it up on the next tear down
Click to expand...

hi all, i did this mod and probably butchered it a little bit, i also widened the intake and exhaust ports on the inside, and i opened up my intake a bit. however, my bike now runs quite badly, no low end power, and decrease in top end and mid range. now i was just fiddling around and its no ones fault but my own. i've tried leaning and enriching, and getting rid of the base gasket too. (i know for a fact i dont have any leaks) now i do have rather OLD two stroke oil im using, and that may be part of the fault, but i doubt it.

anyway, im wondering if you had to adjust anything after you did this mod?
 
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