Most MSR problems resolve easily once you isolate the cause. The symptoms are typically either (1) no fuel flow at all, or (2) no fuel pressure.
(1) No fuel flow can be caused by debris right at the shaker jet. That can be cleaned by shaking the needle in the jet, or poking your own needle down into the jet. In a bad case, the debris plug is lower down, but it is typically still somewhere below the burner. The debris could be carbon that has gone down from the jet, or it could be debris that has come through the fuel line. Once I had plastic that had come through the fuel line and then melted underneath the burner.
(2) Fuel pressure problems can be tricky. You might get just a bit of fuel flow and you get a yellow flame, but not the blue flame that you expect. First, make sure that the fuel pump is oriented with the liquid line and pressure line correct. Second, make sure that the pump leather gasket on the plunger is good. I always squirt a few drops of oil on it before each trip. Once I had to lube it in the field, and that is why I carry Chapstick. Fuel pressure can also be too high, so the burner works but it blows itself out. Also, a few people try to fill their fuel bottle to the last drop, and without a head space in the bottle, things don't work so good.