need some help

It sounds like your motor is not actually starting. When you have no spark it will sound much like you're describing. Take the spark plug out and reattach the plug wire. Ground the plug against your motor as you turn the rear wheel, if you don't see a spark then you have almost found the solution. If there is no spark it could be because of your plug, plug wire, CDI or magneto.

Make sure you have spark first and if not we will see if we can help you find out what exactly is the problem.

yeah, sounds like grounding out, or not getting fuel- make sure the petcock is open, make sure the kil switch isn't stuck closed or partly- you can disconnect entirely to eliminate as a factor or not..

When it`s doing that, reach down and mess with the choke lever up and down along with the throttle....It`s quit the technique but sometimes it`s what ya gotta do.....

If your'e certain you've got "good" spark, (nice and bright dancing on the electrode) while pedaling fast (tie up rear and have friend hold bars) so to pedal in stationary position - spark plug laying on top of cylinder head to see.... if bright spark, check your carb by unscrewing the top where the threaded cable goes in (loosen the cable nut and adjustment screw in top) and unscrew the bonet that threads onto the body of the carb. Check if the piston and needle are free. Is the piston aligned with the slot and it's alignment pin? Assemble... does it respond all the way open-up and fall down-closed with twist of throttle? if all's good try again, making sure of proper choke usage and good fuel mix.

mike bike sounds/acts like that when the choke is on (so when its running rich) make sure the choke is securely off (a rubber band works to hold it) and if it still acts up then move your eclip on the carb needle up one notch and see what that gets ya

I have to agree with Nunya,I built many MB"s and almost everytime I had that poblem it was because the killswitch wires/Cdi wires were not hooked up properly, so it was grounding out,if both things are hooked up right and its still doing it,check the magneto coil,and spark plug.It's always a good Idea to have a extra magneto coil laying around,I've seen more then a few go bad.