Motorcycle Repair: 74 Dt250 Cutting Out, yamaha dt250, fuel mixture

Question
Hi there. I have a 1974 Yamaha Dt250. A few weeks ago it started cutting out
at around 5000 rpm. Before it would go over 6000 and run just fine. It's really
iffy. Sometimes it will do it, and other times it won't. I made sure the petcock
was clean, and I recently cleaned out the carb. It seems to me that it's a fuel
problem, because if you shut the gas off, right before it runs completely out
it will run excellently. I'd really appreciate any help. Thanks!

Answer
Matt,

when you shut off the gas it starts
to lean out the fuel mixture which
indicates your problem is probably
due to excess fuel.

This could be a few things.
One- is a plugged exhaust pipe.
Two- is a main jet that is a size too large.
Three- is a blocked air filter or air box.
Four- is a faulty or leaking choke plunger.
Five- float level too high or leaking float valve.