Carb issues

I have a 91 CR250 that I took out this weekend and I’m having some problems with it. The previous week the bike ran flawlessly with out any problems. However, on Sunday it was running very rough and was burning through a lot of fuel. Normally I run NGK BR8EG plugs in it but I go around I tried a cheaper plug, NGK BR8ES. I maintained the same ratio 40:1 BelRay MC1. At 3/4 to full throttle the bike would run fine. At lower RPM the bike would smoke a lot and burble quite a bit. It was burning through twice as much fuel as it should have.

Went back to the trailhead and switched back to NGK BR8EG plug and tried to tune the air and fuel ratio to smooth it out. No luck. At higher RPM the bike would smooth out and run just fine. Any lower and the burble was back.

My first though was that the float was sticking but I didn’t see the carb pee any. I’d blame it on the jetting but just a week before the bike ran fine.

I did notice that there was a small air leak between the carb and reed cage. Wouldn’t that cause the bike to rev to the moon? I tightened it up but still no luck.

The top end isn’t that old, maybe 10 but no more then 14 or 15 hours on it. The air filter was clean. I’m out of ideas. Should I just spend the money and have the carb rebuilt or do any of you have any other thoughts at what I should look at.

Any help would be appreciated.

Mike