85r fouls plug on every warmup?

[kxt250r]

i recently had an airleak which i believe was around the manifold and the bike would not idle. now that is fixed it idles well, but every time i warm the bike up it fouls a plug, either when its revved or not. (when running its fine and wont foul plugs)
have not made any mods and all the carb settings should be sweet..
cant work this out??
thanks

[cr480r]

turn the choke off after it fires...

[kxt250r]

turn the choke off after it fires...

that's what i do already..?

[ceaserthethird]

Whats your Oil mix ?

[BigGreenMachine]

Sounds like a trans side crank seal problem to me.

[jeffatc250r]

BGM has a good point, is your bike losing tranny oil? and does your exhaust smell nasty?