Yerf Dog runs rough and back fires

[cpa]

Hi all, my Yerf Dog 250 cc Go Kart starts great and idles well but when you rev it up it misses and backfires. I have cleaned the carb, checked electrical connections and have a new battery in it. Normally would change the mixture (no adjustments) or the timing (is all electronic) so I am out of ideas. Any suggestions? Thank you in advance for your help!

[xlint89]

What model do you have? I don't recall them ever using a 250cc

[cpa]

You have a good memory, I took my sons word for the motor size (bad move!). I checked in the Yerf Dog website and it is a 150 cc Model 3209 Kart. That help?

[x-bird]

Maybe valves are out of adjustment.