My bike doesn't want to turn over. It ran just fine last week, but something has changed. I have enough power with a new battery and I can hear the motorcycle trying to turn over. The exhaust pipe puts out some exhaust, but the engine won't take over. When this first happened, the bike ran for about 4 seconds and then it would die. Now, it won't turn over at all. I don't know what to diagnose as the problem. Tips? Thanks.
Your description was really vague, but here is some thoughts. From what I gather, engine does turn over (i.e. it actually spins), just does not start.
For the engine to start, you need two major ingredients: fuel and spark. Obvious first things is to check if fuel is in the tank, and pet-cock is open (if available). Spark can be checked by taking the spark plug out, putting electrode to the engine block with wire on (careful to stay insulated to avoid shock), and cranking the engine to see if spark appears. By the condition of the plug you can also see if the engine was flooded with fuel (that is why there is a pet-cock on carburetted engines).
If these obvious things check out, see if the fuel gets to the cylinders. Close the pet-cock, disconnect the hose, open the pet-cock, see if fuel goes through. Repeat the procedure down the line all the way to intake ports.
Those are basic engine no-start troubleshooting steps. Other than that, we need more information: how well was it working before, what is your experience with motorcycles, and how long have you owned it? Was it just out of storage (if that, was the fuel drained or stabilized?), or used regularly? Was it maintained well? Etc. etc.