KTM 250-Doesn't start -backfires

[ndejesu]

I bought a used KTM 250 1996 which ran, but without much power due to bogging down in 2nd/3rd gear. I took it to the KTM dealer after attempting to clean the carb, lower the needle, and change the gas. They cleaned the carb and verified that the compression is good and it is getting a spark. Now the bike doesn't start and when push start, it backfires once (real loud). Does anyone know if the powervalve malfunction would exhibit this behavior?

[bajadog]

I have a power valve that was completely stuck closed, it still
started but had no top end.

It sounds like ignition timing to me.

[ndejesu]

Update: I sold the bike and the guy who bought it called me back to tell me he got it running. There were two things wrong with the bike:
1. The reed valve was cracked/damaged and needed to be replaced.
2. The key on the timing flywheel was sheared and was causing the timing to be off.
Once he got those things fixed, the bike ran fine.