Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Re: optimal operating temp?
I'd guess it's not vapor lock. Vapor lock occurs when fuel boils in the pump, because it can't pump vapor. If it were vapor locked, there would still be fuel in the float bowl. It would start easily, but then die after 10 or 15 seconds.
It's more likely that fuel is boiling out of the carb and puddling in the manifold, flooding the engine as soon as it starts to crank. Or boiling the carb dry so there's no gas to start on. Or, maybe most likely, it's boiling in the pump which is pushing it past a leaky needle valve and flooding the engine.
I'd check the easy things, like timing, and if it persists, do a quick rebuild of the carb and set everything to spec.
Also make sure the heat riser is opening. If it's stuck closed it can make the manifold under the carb very hot.