what bike /engine is this?

[user 20441]

i just got this bike, it rides well, until it gets hot, then it stalls and can't start it again.
might be ignition related i think.
first thought of valves not having enough clearance,those were good.
it's got a 22mm carb (inlet rubber is only 21mm,will match this to 22mm)
97.5MJ and 15PJ.

it says in the handlebars : genuine thumpstar , but is it real??
it sits on 2x 10 inch wheels, very plush rear suspension and (leaking) upside down forks.

can anyone identify the alloy frame and that engine (would this be a gpx?)
it's got a GONGYU cilinder and gives 125cc.
it's more powerfull then my lifan 124cc...

look at the location of the clutch lever on the engine (not on the crank, meaning it would be a better engine)

thanks for the help on dentifying this toy

 

[user 20441]

nevermind that location of that carb,i was testing a slightly bigger carb that wouldn't fit under the tank,so had to twist forwards.

 

[motodevo]

That is a gen thumpstar frame, probably the most desireable one being the billet frame one. The engine looks to possibly be a yx125 with secondary clutch (i have engine with gongyu on it that is marked as a yx). Next time it gets hot and wont start, pull the lead and check for spark, that would confirm ignition probs. And it goes without saying, start with a new plug, there only a few dollars but some guys waste hours chasing faults down to a faulty plug. Also crack the carb bowl drain plug when it happens to make sure there is not a restriction in fuel flow causing it.
Nice little 50 style bike

 

[user 20441]

a different spark plug brought the sollution, easy peasy :-D
the engine number stamped on it is 156FMI but i read this code still is no guarantee to identify your engine?

 

[motodevo]

156fmi is a common style serial number for chinese made engines independant of the actual engine manufacturer. 1 means 1 cylinder, 56 means 56mm bore. Many upright/vertical (rather than horizontal like a pitbike cylinder)chinese 125cc also start with 156fmi

 

[user 20441]

can i fit for example, an yx 160 under this frame (without clearance issues for the carb,wich i allready have somewhat now with the 125...)
and what about those forks, are they any good for recreational use (the need servicing), no heavy jumping?
and what gearing works fine? 1st right now is like i could climb a vertical wall