Totally pointless- adding power and efficency to a 66cc chinese bicycle moped... - Page 2 - Fuelly Forums
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Old 07-26-2009, 07:11 PM   #11
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chinese engine= blow up soon enough without trying to do so.

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Old 08-13-2009, 02:59 PM   #12
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Having had a number of 2 strokes, in stock configuration they are made to go through every kind of weather and traffic conditions without hassle. Also the economics of factory assembly, the cheaper the scoot, the more cost savings went into its production.

In the 80's I had an RD250 Yamaha twin 2 stroke. I replaced the cylinders and pistons with 350 units, added a DG head that raised the stock compression from 7.4 to 9.5 to 1, added Bassani expansion chambers for exhaust, swapped the 28 mm carbs for 34 mm carbs. In the end it had the power of a 900 cc bike. The trade off was I went from 42 mpg to 18 mpg !!! With help from my local Yamaha dealer, he showed me how to jet it leaner, play with needle sizes in the carburators to get the bike back some MPG. After that I got between 28 to 34 MPG, that was liveable.

With allot of the scoots out there especially the 50 cc class, a pipe and carb will will raise your upper RPM and that way increase your speed, because you can't change your final drive ratio. If you check out, they have dozen of stories. Youtube more than likely has your scoot modified, and you can follow the trail to see what they did.

With your bike, if you can get a Mikuni carb kit for it, that may be better than the stock carb by providing better atomization of the fuel. If you do add an expansion chamber, limit if you can the exhaust outlet size. An expansion chamber works like a reverse supercharger, the chamber creates a vacuum effect, making the exhaust pressure lower, drawing in a larger volume of fuel. If you have ever added an expansion chamber to a stock bike, its a rush, once up in the RPM band, the expansion chamber goes into action and the bike leaps away. To cover all this extra power, you have to add fuel, therby making your MPG go down.

Defentely go out and play, tear it appart, its a tone of fun. I don't know if there is an 80cc kit for it, it would be interesting to see how many after market perormance parts would make better MPG. Little things like advancing the spark a degree or two might make better MPG, advance it too much and you'll overheat, overheating a 2 stroke means seazing the piston.

Taking the cylinder head and milling it down a millimeter could give you a bump on compression, there is some more MPG. Going to a Bosch platinum can help. A pile of little things can add up to a big thing. Enjoy.

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Old 08-13-2009, 03:04 PM   #13
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Oh yeah I forgot, if your scoot has a variator, or variable transmission, you can remove or sand down the limiting washer on the engine side of the drive pulley, with this it will make the cones come closer together and raise your final drive ratio, making your gears taller by 1 or 2 percent.
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Old 08-13-2009, 03:48 PM   #14
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A medium/low ported 2 stroke will give more pull down low and allow a lower rpm for normal cruising.

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