40 MPH Club

Thanks! It is starting to come along. I hope when it goes back together this time I start to see the results I'm looking for. It was finally starting to feel and sound like a proper two stroke with a smooth hitting power band pulling cleanly to the top with no 4 stroking or flat spots. It's taken a lot of work.
 
Welcome to the 40mph club beginner01! I will be trying to re join soon with a 49cc Huasheng 4 stroke on a beach cruiser. It may turn out to be a bigger challenge than Bonneville with a China Girl ha ha.
 
Coaxing 40mph out of a 49cc 4 stroker will be a good challenge... it can be done but won't be quite as easy...
With some careful port work, bigger valves,bigger carb, a tuned pipe (stepped type header), and a cam (if available ) and give it lots of compression and it should make it, best bet would be to set it up to make lots of top end power, lots of rpm, and gear it down and/or find a way to make a cvt work and 40mph should become fairly easy to reach. You could run it on methanol or even a nitro blend will also help.
 
The cam is available and I will port it even though they say not much can be done. Compression is fixed on the Huasheng, but I have a couple ideas that might work. I have an aluminum intake manifold partially built out of half a Briggs V-twin manifold, I'm sure I will have some work to port match it and line up the bolt holes. I have read up on header designs and that should be straight forward. And you know I like nitro blended with methanol, the China Girl took to it really well. If the Huasheng seems strong enough I may try the same percentage I ran in the CG since I have baseline jetting math that should be close. I will have to blend my own though. With the 2 stroke I took the easy way out and bought off the shelf R/C fuel but it had a ton of castor oil in it and I don't want or need that in the tiny thumper.
 
There is a huge variety of pre blended nitro fuel available for R/C cars and planes. Everything from 5% up to 50% nitro to methanol blend but they use huge amounts of castor oil in the blends. I was able to make it work with the emulsion tube drilled as far as I could then one size bit up from that on the jet with an RT carb fed by a Briggs V-twin pulse pump. You have to try to achieve 6 times the fuel flow rate of gasoline. It actually burns cooler and makes roughly 3 maybe close to 4 times the combustion force of gas. It's a very quick way to explode engines obviously. Mine held together for a few wide open passes on our test road. I have a balanced crank and tapped the cases to 3/8 and had grade 8 bolts ran down thru the head for studs.
 
The whole set up wouldn't idle or even run below probably about 3500 rpm but it made a bunch of power at wide open throttle and high revs. I only tried the 20% blend but with a bunch of trial and error could find a mixture that would run ok I'm sure. I just needed wide open top speed power so that was all I tried for. Happy Motoring!
 
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43 mph they said but would not write a ticket for it @ 15:54
 
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This is a stock 66cc with a 700C rear and 26" front, 42 tooth rear, it will max out at 32mph checked by a properly calibrated speedo and a reality check with a gps speedo app on my iPhone. Don't think it could go much faster no matter what gearing was used. Larry
 
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