HP61 Gold Cup
This is an Austrian engine from the Hirtenberger Patronen factory. The black Thermax coating is used to enhance heat emmissivity. HP engines are now made in the US. For some history have a look at the link above. It's said that the fellow who designed these engines also designed the Webras, which would account for the general similarity. The construction is ABCD with'D' standing for Dykes ring. The carb barrel cross slides like the Webra Dynamix although it is round in section whereas the Dynamix is rectangular. A unique feature of the carb is an accelerator pump. There is a spring loaded piston in a chamber near the fuel inlet. The chamber is visible to the left in the picture just under the drive washer. When the barrel slides in to close the venturi the needle passes through a hole and pushes the piston back against spring pressure. Fuel accumulates in front of the piston. When the barrel is suddenly opened the spring pushes extra fuel into the venturi.