250 Big Red cuts out half throttle

[85 big red 250]

I was wondering if anyone had a similar problem. It still fires right up and idles fine but as soon as you push the throttle past a certain point it starts to bog down.
Thanks

[McDerry]

Plugged main jet. Theres three jets feeding fuel to the dual valve carb. Will run from idle through about 1/2 throttle on the two smaller jets, but won't run past 1/2 throttle if the main is clogged.