Strange sound

[tombenn444]

Okay so I recently addied some custom exhaust that I pulled off of a two-stroke mini bike and it sounds good has a decent power I haven't really opened it up yet since I'm having some trouble with my sprocket adapter and the roads are a little wet right now but anywho I'm getting a strange popping sound about two times a second on 3/4 throttle and I'm wondering what it is is my exhaust too long I'm having too much unburned gas in the pipe is the back pressure too much?

 

[Chainlube]

Sounds like it's 4 stroking.