new motor break in

\this motor is only running smoth during acceleration, once it levels out it runs rough, i let it slow down and give it gas and it will run smooth until it quits acelerting, im not rappin it out it, does this even at half throttle

i think i'd start by checking for air leaks on the intake side - carburettor etc, intake head gasket; guys do this by spraying wd 40 around the sus area of the intake while it's running at a constant fast tickover & listening for a change in engine note

you have to contrive to avoid the wd 40 getting into the actual airfilter intake of course

trying another sparkplug & checking the gap at the same time is always a good idea too....

i run into this all of the time. try a different carb slide needle. you may have to try a few different ones, before finding one that wont do that.
or you can chuck the needle in a drill, and take some really fine-grit sandpaper and roll it between your fingers. not much, though....we're talking microns. bikeguy joe can explain it better.

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it's normal for them to cruise under 4 stroke.. mine even seems to gain more power when it's 4 stroking.. once it goes 2. my MPH will back off, let off and let it4 stroke and it'll pick back up

160 miles and absolutely no power, seems to have little compression as well, i ordered another motor that should be here tomorrow, i changed carb slide needles and than tried a whole different carb that i know is a good running carb and that didnt work either, thanks for the replies.

For what its worth, I had/have similar experiences. New motor is rough during break in. Tried the old carb that was proven but it didn't like the new motor. I have no clue why since there was no air leaks. New carb is better but it is still tough to start cold. A lot of 4 stroking yesterday. Hotter plug today and although it was rough at first it seems to run better now. I did 15 miles earlier and let it cool for a couple of hours to test the cold start. It's not ideal but a lot better than yesterday.

If you have a Harbor Freight near by, they sell a compression checker for $9. I picked one up yesterday. I had never used one but it is quite simple. Pull the plug, screw the checker in the head, pedal and pop the clutch. The gauge will keep the highest reading.

FYI I think I read elsewhere that it is bad for the CDI to not have a load on it. So- you can leave a plug in the plug wire just dangling to the side while you check compression. Don't let the plug touch your thigh with shorts on!!

If nothing more, you'll have plenty of spare parts for the new kit.

If you are using acorn nuts on your head bolts, they probably are loose and you may have power loss from blowby past the headgasket....very common issue for no power.

Also what angle is your Carb intake at? Is your bowl level?

Thanks for the replys, put a new carb on and sealed the heck out of it with black permitex gasket maker and eliminated the air leaks, i also put the carb slide needle to the top and the motor is running better and better, real zippy when accelerating, i am also running a stock pipe for the run in to properly seat the rings, must have back pressure to avoid washing out the rings, will put modified pipe on later, Thanks again

That's completely normal, before break in is complete. After that, you SHOIULS break into a four cycle when not under load. A properly running piston ported 2 stroke will break back and forth between a four cycle and a two cycle at cruise, breaking into a clean two cycle when the throttle is opened.

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