I just had problems with my 375 sprint. After much checking of all parts, replacing diaphragm and primer, Still had trouble.
My problem was different in the fact it was starving. Start up was fine, but would suck in the primer then stall.
In anycase, perhaps remove and check you main pickup tube. I blew mine through many times and it was always clear. On the 3rd time around I pulled it and ran some fluid through. What happened was a dark spot appeared. It was a fine ball of blondish hair that darkened when wet, but moved freely when I passed the air through it. So when the fuel went in,it swelled and blocked the jet! Its worth a try to pull it and make certain. Not entirely an issue id relate fully to your symptoms, but worth a try if you've checked everything, and its getting no fuel.
The other ball is fixed and is a gallery block, and id doubt it will be any cause for issue. Make sure your diaphragm is the right way up, if applicable to your carb.
