79DT250

So i recently bought my dt 250 and it was running great for a few days and then it died, I finally got it started up the other day and it wont go past 4k rpms when im driving it. ive tried everything i can think of with the carb and i can get it running good for about 10 minutes. it idles just fine just not when driving it? it leaks from the head gasket? idk if maybe a vacuum leak or something would be causing my problem.

I just bought a 79 Dt250 and its an awesome bike. Looking to do some upgrades and a few body changes with it. Having a few problems with it hopefully you guys can help me figure it out.