Rough Midrange

I'm running in my 66cc beastie, it's only got 80km on the clock at the moment.

She fires up easily enough using choke, within 2-3 mins runs well with choke off.

Low range pulling is fantastic but when I get the speed up it sounds like it's faultering. Almost like it's only firing every second stroke.

The plug has no residue on it, still shiny silver, running 20:1 mix, blue smoke at mid throttle to WOT.

Any ideas???

be gentle with your breakin period.
have you ported the exhaust pipe?-basically cut the gasket to fit the exhaust port and then taper the exhaust flange to match to gasket opening. my engine completely changed after that

after you start it up-be sure to let it warm up a 1 minute or so.

regularly check the air filter for oil and clogs-I can usually start my bike with no choke (in august anyway) just use choke to stop it.

I've never had this confirmed but make sure the magnet is centered in the magneto coil. who knows-you end up checking everything on your ride eventually but porting is usually the first performance mod after sparkplug/wire upgrade.

suerte.
jon

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Break-in is best accomplished with the use of various throttle positions and engine speeds- don't be afraid to run it up once in awhuile, it's not going to grenade just because it's new. Baby-ing a new engine will not help in any way.

Now, these engines are piston ported crude old school engines. You are a little rich in the mid range from the sounds of it. These engines will break into a four cycle when they are not loaded (going up hill/speeding up/ect) if they are set right. If you are trying to speed up from mid range and it still is four cycling, you are too rich. If it breaks into a clean two cycle with application of throttle, you are in pretty good shape.

In my experience at least, if you get these things to run in a nice clean two cycle all the time, they are too lean and suffer not only in power, but engine longevity. (wristpin, bottom end bearings).

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If it ain't broke, and you mess with it long enough, it will be.

Also, go to 24:1 after the first tank. Going from 20:1 to 24:1 will make the engine run slightly richer, so you have to change the "C" clip.

Once dialed in, you plug should be a medium to dark brown in color.

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If it ain't broke, and you mess with it long enough, it will be.