Try running it with the air filter and housing off from it.
A little story to go with that.
When i was 17 i went on a 1200 mile trip delivering some sculptures.
The boss had bought this old ford full size van. it had a 460 in it but didn't run well at all. We did the full tune up on it and it ran much better.
Loaded up the van. and took off. we soon found out that it just wouldn't do freeway speed if there was any up hill to it.
100 miles down the road the we had burn up a full tank of fuel.
We tried several thing but what fix it was when we chucked the hole air cleaner assemble in the back and took off. Mileage tripled. wow, pull any hill..................until the eng when boom 400 miles down the road.
ops:
I still, to this day do not know why the air cleaner housing caused such a over rich condition. But it did.
It's a simple test, give it a try.