2002 cr250 Choppy idle, erratic PINGS

Well iv Had this problem before and i thought it was because it was sucking air where i had cracked my crank case. but had it welded by a company which did a good job. And I just put a new OEM Honda piston and rings and gaskets, But once the Bike warms up to around 70 C, When i go Slow in first gear the idle will jump up and as it comes down it has a unusually loud and distinctive pings. This is not a regular common 2 stroke ping. Its like a, PINNG....PING.......PING.....PING, Really loud As the rev comes back down Any suggestion. Ill try to get a video of it Tomorrow. And the new Parts only have about 20 min on them.

the plug does look good and it has not done it sense then, the bike has 0.4 hours on it and I haven't had any other problems, starts first kick every time.