kat not running right please help

[tazz7951]

I bought a 96 kat 600 for my girlfriend. the bike was running great when i bought it. I was also a previous owner of this bike so i know how the bike has been maintained. This is my girlfriends first bike and she didn't really know how to ride so i was letting her ride the bike around the house. This way she could learn how to start and stop without the bike going dead on her. It was all very slow speed and i would stop her every now and then to make sure the bike wasn't getting too hot, which it didn't. I got on the bike the other day to take it down the road and when i would try to accelerate from 45mph it would spit and sputter. If i would take off pretty hard from a dead stop it would do it no problem but maybe backfire some when i let of the gas to slow back down. can someone please give me some advise?

[HungLow]

fule filter i would take a look at it or just replace it it sounds like is plugged

[Slofuze]

You may have fouled the plugs. I'd start there.