You are on a 2 stroke so here is my check list as I see it for when your bike is running great, then not so great. This list makes some assumptions... You have a clean air filter, and nothing extra ordinary has happened, bike swamped, hole in the case-ran it out of oil, you aren't riding at 6000 feet elevation when you normally ride at sea level, yadda yadda. I am no expert but here is my check list: 1- SPARK: Put a new plug in, check for spark. It can oil up and foul. 2- COMPRESSION: Test time! Not with your thumb, or whatever druid ritual you devise to convince yourself it has "enough" compression. Engines where out... test it. it can be a fresh rebuild and something goes wrong. CHECK IT. Ask around, borrow, buy one.... you need to know what your engine is doing and this is a great tool.... I am not being a jerk when I ask "How much Psi does your bike have?" I am a jerk for so many other things, this is not one of them. 3- FUEL: Odds are if it worked yesterday it is still going to work today. Are you getting fuel into your cylinder? A new plug would get wet if it didn't start right away to let you know you have gas getting in there. You could have debris in a jet but to get something in there you probably swamped your bike or something else extra ordinary happened (see earlier assumptions) If you have fuel delivery, full compression, and spark you should at least have fire. Now other items can throw things a curve ball but are less frequent. The next are in no specific order: 4- Clogged Vent Tube. Those little anodized aluminum things people put on gas caps instead of running a tube into their steering tube clog easily and can create a vacuum so you bike will have some fuel but then soon enough no gas can get from tank to carb. Seen it numerous times. If you can take your gas cap off and hear it suck air, take that damn aluminum thing off. Actually carb vent tubes can clog too but 4- Cracked Reeds. They talk about it on this sight but I haven't actually been witness to it myself. 4- Electrical. Rare enough but possible. Computer going south, spark plug cap/wire problem 4- Crank seal. Yeah you Steam Engine McCloud Maker. 4- I am tired but there are lots of other things there can be BUT you need to try 1, 2, and 3...... FIRST . . . . . . . . For the love of Zeus.... every time a bike runs weird it isn't the jetting. Odds are a nymph didn't come in the middle of the night and change your jetting. It is a pretty low wear item. This, of course, assumes it was running alright before and you didn't just pick up a basket case from someone else who tried to fix his compression problem by changing the jetting all over the place. (I am kind of in a mood) Luv all of ya'll guys, regulars and newbies! Some of these questions get repetitive.