Priming

[tarp]

Hover,

I stand by my answer for older O-360 engines found on the Cherokee 180's, Archers, Seminoles (at least up to 1979 which is the manual I own), etc. I have no idea what extra "piping" may be on the 2000 model Seminoles.

Skeezer,

The reference to "pumping" the throttle forward twice is to activate what many call the "accelerator pump" inside a carbureted engine. The accelerator pump is just a simple valve that allows a little bit of gasoline into the throttle body (venturi) of the carburetor without the aid of the vacuum pressure from the engine.

A lot of folks advocate using this as a "primer", however it can be dangerous in the event of a backfire. Since you have now provided a ready fuel source so high in the system, you can literally set your air filter on fire or worse if the engine backfires.

Generally, two pumps of the throttle on a warm engine without any other "prime" will be plenty of fuel to get the engine to turn over. The danger comes in when people keep pumping and pumping loading up the carb with fuel.

Follow the manufacturers suggested starting procedures but always use the "cold", "warm" and "hot" engine sections of these starting procedures as they are written.

 

[DC9stick]

When I flew the Twin Beech, The real Twin Beech P&W 985 tailwheel, When the weather got chilly we pumped the throttle as fast as we could while cranking the engine, a large puddle of fuel would form under the engine and sooner or sometimes later the engine would backfire setting the puddle on FIRE! By the time you got out of the seat crawled out the window ran down the wing opened the cargo door grabbed the extinguisher and put out the fire the engine had been preheated from the bottom and would then start. On really cold days you repeated the preheating process until succesful or the battery was dead.

I have witnessed numerous pilots cranking and pumping the throttles on FUEL INJECTED engines, this does nothing except cause the butterfly valve in the injection unit to flap open and shut and is seldom sucessful.