The last comment about the brass filter sealing off due to ethanol fired a dormant synapse.

If you have the brass element nozzle filters they could be stopped up and causing the problem. I had this happen on a sprint car. The filters had been cleaned regularly, but over time they built up enough fine stuff in there that they quit flowing. I replaced them and that took care of it. You could ultrasonic clean them with a jewelry cleaner too.

I found those filters at Grainger pretty cheap. They were actually an air tool muffler.