Fuel injection Lycoming vs Continental
I am sure many of us have heard the unfortunate sound of a Lycoming engine being cranked repeatedly and not starting. Walking out of the hangar to have a look, one invariably finds a Lycoming powered Piper Arrow or a Mooney with a hapless operator desperately trying
to start the plane and eventually running the battery flat.
The problem invariably is that the engine has been flooded and usually this was a ‘hot start.’ The problem often lies with misconceptions about how to prime the engine with fuel and that the Lycoming injection system is very different from the Continental system. I am speaking generally here and not referring to any specific engine, but the common types found in many light aircraft. For example, a Seneca V is not a typical Continental Injection System).
Starting a Continental IO/TSIO 360/470/520 is all much the same. Fuel on - Master on -Throttle and mixture full and hit the primer / fuel pump switch. Fuel flow rises to its peak on electric pump and leave it there for a few seconds and then switch the pump off. By now fuel is coming out of the overflow pipes onto the ground which is common. Throttle set to idle plus a little – mixture full rich, crank and the engine will start after a few turns. Hot start is much the same except that one may have to feed in fuel in via the electric pump to keep things going. Try the above on a Lycoming engine and you will be incredibly lucky to get it started. If the engine is hot it is almost guaranteed that it will not start; this is where the cranking repeatedly comes in.
I am sure many of us have heard the term ‘re-circulating the fuel’ when it comes to priming. I have heard this many times especially when trying to assist owners / operators with hot starts. It is important to understand that typically Lycoming engines use the RSA / Bendix type fuel injection system and Continental uses its own version which is completely different in its function other than they are both constant flow with flow dividers. Fuel injected Continental engines have an engine driven fuel pump with a vapour separator which in fact does return some fuel to the tanks. However, this will only function when the engine is running and not when priming for start.
There is no such thing on a Lycoming with
RSA / Bendix injection system
Therefore, the term ‘re-circulate fuel’ is a myth in both type engines. What is possibly correct is that with a hot engine the fuel in the flow divider, injector lines and other associated pluming may have vaporised and there is no fuel in the lines.
Applying primer pump will obviously fill the lines again with fuel and ‘purge’ any air in the system, but not re-circulate as there is nowhere to re circulate to. Why the difference? Opinions vary, but most popular opinion is simply the design of the induction system between the two manufacturers.