Just disconnect the pipe from the engine and see if it'll start.
When I got my Jawa it ran great for 2 days, then 30 seconds after I started it it died. I took apart the carb several times thinking something was in the carb. I was finally able to start it after pedaling my ass off for 15 seconds, but it didn't have any power and I could only keep it running at high rpm and as soon I let off the throttle it would die. Then it eventually wouldn't start at all even though I had spark at the coil. When I found a coil for it and put it in the spark was way brighter than the old coil.
Are coils that hard to find for Jawas?? I was able to find one in a week or so from someone on here a few months ago.