scoot just kinda quit producing power

[vs7]

150cc gy6
On the last leg of a 15 mile ride my bike just started making loud popping sounds, which might sound like sputtering through a stock muffler. I lost power immediately. After pulling over to make sure my exhaust pipe wasn't broken I tried to accelerate, but almost instantly it was nothing but just popping and bogging.


About a month ago I was forced to ride home about 5 miles with no muffler(I kept it at 10 mph or so), as the stock one broke off. Every thing has seemed fine, except every time I check the exhaust valve there is no clearance, even though I always adjust it to .004". Could I have ruined the valve? Would that cause these symptoms? Is an exhaust valve difficult to replace?


Any advice will be greatly appreciated. Not looking forward to a 20 mile round trip bicycle ride to work tomorrow.