The seats can absolutely swell and restrict fuel flow, I have had that happen 2 or 3 times already.
Some HL carburetors have a high speed check valve, some do not. I'm not sure if the "do not" class use a sintered metal capillary seal like the MAC carburetors. In either case I think you need to pop the welch plugs out and see why fuel isn't flowing through the H circuit.
Looking at the IPL again, the HL63 does have a check valve, you may have to take extra measures to make sure it is clean and passing fuel.
Mark Heimann
Some HL carburetors have a high speed check valve, some do not. I'm not sure if the "do not" class use a sintered metal capillary seal like the MAC carburetors. In either case I think you need to pop the welch plugs out and see why fuel isn't flowing through the H circuit.
Looking at the IPL again, the HL63 does have a check valve, you may have to take extra measures to make sure it is clean and passing fuel.
Mark Heimann