Ok I am a mechanic and i have also owned and worked on several of theses 150cc motors. Sadley i dont know whats wrong with mine This baja has a neutral so it is easy to duplicate concern. When i rev it up it seems to cut out as if it has a rev limiter. It does this while driving just the same. I swapped the cdi with a performance "orange" cdi off of my talaon. does the same time. I dont know if this "performance" cdi has a no rev limtit but i do know i can dog the crap out of my talaon with this on and it does not cut out. So im thinking its something else. The engine does not bog down at any other time just once the rpms get pretty high. i dont have a tach so i dont know how many rpms im turning but again ive owned plenty of these buggies and have not had this problem. ive got a video i will try and post. any help please let me know. No other modifications have been done to this that i can tell. Thanks again for any help

have you tried adjusting the valves i have had one to tight and cut out at a high rpm
its been a while ago now but i think i have floated my valves out before.but it was on black top down hill and wide open. i was running 10 gram sliders ,1500 spring ,bigger axle sprocket, gear low. it was screaming i know it was going over 9000 rpms had to be.
stock buggy think it would be hard to do just my opinion

also have you checked you grounds, wires plugging on to coil,
also check coil wire to make sure its tight in coil, plug cap also.
you can unscrew wire out cut some off wire and screw it back on.
maybe even try a new spark plug.

i tried to watch you video but couldn't

I also tried another coil that i had. Brand new again "orange" performance coil. did same thing. I dont know how to adjust valves do you know how or have a thread i could look at? You can feel it do the cutting out just before if shifts as when the rollers must be going out because it cuts out then gains speed then cuts out again. if you do donuts it does it also. Acts just like a rev limiter but i know that cant be the problem. ill try and post video again i dont know why you couldnt see it though. i took it with my i-phone then sent to my e-mail. do you have e-mail i might could send it that way

your video was probably fine, my computer just said i don't have the program to run quick time, which i thought i had.

are you sure your not haveing a gas problem not keeping enough gas in the carb bowl.
also grounds have to be good to or at a high rpm you will lose spark and cut out,i had paint on my cvt cover when i first got mine that had me looking into things that wasn't the problem.

valves are just common maintenance on these engines they need to be adjust regular, they will sneak up on you
there is a service manual section here in board index any gy6 will work.
check one out just have to get piston on tdc compression stroke,cam ligned up than adjust i think most just go .004 on intake and exhaust valve
check a manual out if you have a question just ask some one here will lend you a hand

ok so got home with new ideas. took off air filter duct and started up, when i rev it up and it starts cutting out lots of fuel vapor comes out carb. so im still thinking valve or carb problem now. Any ideas? ill take carb off tomorrow i guess and clean and see what happens. heres another video tell me what you think please

just found it broken intake valve spring will post video tomorrow

you can change the valve spring without removeing the head. just need to get the piston to tdc and pack small rope or use compressed air to hold the valve up