To check the reeds you'll have to pull the reed block out and have a look. Look for chipped or frayed edges around the ends of the petals.
These things are hard to diagnose without being there to see/hear it. Since it sounds like you have compression, that only leaves spark and fuel to be the culprits. Your not getting one or the other. I noticed you said you "cleaned" the plug. I have never had any luck with doing this, best bet is to replace it.
Edit: Reread your last post and noticed something else. In your ready to start sequence you said you "turned on the ignition switch". Where did an ignition switch come from? There are no ignition switches on motocross bikes. Always on until you hit the kill switch. This sounds like something a previous owner cobbled on there for some reason, and now has drawn my suspect as very possibly the root cause of your problem.
These things are hard to diagnose without being there to see/hear it. Since it sounds like you have compression, that only leaves spark and fuel to be the culprits. Your not getting one or the other. I noticed you said you "cleaned" the plug. I have never had any luck with doing this, best bet is to replace it.
Edit: Reread your last post and noticed something else. In your ready to start sequence you said you "turned on the ignition switch". Where did an ignition switch come from? There are no ignition switches on motocross bikes. Always on until you hit the kill switch. This sounds like something a previous owner cobbled on there for some reason, and now has drawn my suspect as very possibly the root cause of your problem.