Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Here's the problem. With the cylinder separation angle at 45 degrees the intake manifold is very short. As rhe engine heats up the manifold transmits heat into the carb and that causes a vapor lock condition. I'm guessing your engine starts good and runs good for a short time but then starts to falter. Here's a quick check. Watch the fuel line and see if the gas seems to be pushing back when this occurs then put your finger on the carb. I'll bet its hot! Put a small piece of ice against the carb and it should smooth right out. I built a 90 degree V-twin and had the same problem.  The cure was to make insulator spacers between the manifold an head. I think ththese engines just have O ring seals so I don’t know what to tell you.