ORIGINAL: AndyW
Good point, Recycled Flyer. But some traditional diesels have the piston top ride below the bottom of the exhaust port at BDC. So that raw, liquid fuel that's made that nice, fat fillet against the piston goes POURING into the combustion chamber in a gushing torrent causing havoc and mayhem. [X(]
Most diesels in sport controline models and even most racing engines are mounted "sidewinder" style. It is usually a simple matter to completely close the exhaust with the piston when priming, and the closed piston prime excess just follows gravity. Below is a picture of my Nelson 15 F2F diesel. Like most very high performance diesels it has an overflow priming system. The other pic is of my Parra Diesel in a Goodyear model with a home made version.
Both systems divert part of the tank overflow to the closed piston to (hopefully) deliver an instant one flick start during pitstops. Note the potential influence of gravity on the excess.