1985 CR250 Problems. I NEED HELP PLZ.

I have a 1985 CR250 that I have had ALOT of work done too and I am still having problems.I have had it rebuilt,And this was about 2 months ago and when I got it back I had starting problems,And it would take forever to start and when it did start when I get it going when I give it alot of gas it like boggs down and wants to cut off unless I let off the gas.Then I had a waterpump problem and got that fixed and I got it back today and did what the guy said,I put the choke on,Gas on,Gave it no throttle and gave it 4 full kicks and it started fine.But after less than a miniute it just cut off,And I have been trying to start it ever since.Please help,I think it may be a carb prob,But I'm not positive.PLEASE let someone help me I have spent alot of money on it.

Thanks for the reply,Do You think cleaning the carb would help? I don't think it has been cleaned in years.

I think it may just need a good cleaning,Atleast thats what I'm hoping for.I don't think it has been cleaning in alonggg time.The guy who had it before me,Did nothing to the engine and barely ever cleaned the air filter or anything.So my guess is he probably never cleaned the carb either.

Alright I apprecaite the help,And I will put a new plug in and see what happends and I am also going to try some new gas too.