I have experienced this problem many years ago with a conventionally aspirated carburettor fed engine and eventually identified the problem as being due to fuel vapour-lock. Basically what happens is that the fuel line, being close to the engine heats up, vaporising the fuel in the line and as the fuel pump only pumps liquid and not vapour, the engine behaves as if it has run out of petrol. Make sure the fuel line is as far away from hot engine/radiator components as possible and insulate the fuel line if possible, either by installing a sheetmetal heat shield between the line and the engine, or by wrapping the fuel line with lagging (insulative material). If vapour lock is the problem, cooling the fue line will immediately rectify the problem. The only other possible cause is a dodgy ignition coil, which will also break down under the effect of heat. If cooling the fuel line does not fix the problem, replace the ignition coil.