ETLB Squawk Forums — Archive

Quoted from The Termite Will it have electric start?  If it has electric start, then you shouldn't need a primer system,  just a choke or enrichment circuit. I have no problem starting my 503 in the winter, the enrichment circuit / choke does the trick.

I am not an expert in fuel system, but from what I have read, the primer system provides a rich supply of fuel / fuel vapors at inlet manifold for just the first few seconds when engine cranks. After the first few cranks this supply is totally gone. Assuming the engine fires within the first few cranks, the engine still takes about a minute or two to warm up, and till engine reaches operating temperature, we still need the carb to ship choke-enriched fuel into the cylinders.

Between the two,  the choke has a more useful and more substantive role than the primer. Also, how widely is the primer system used ? Is it just a neat trick the home-builders have perfected, or is it more widely used in other applications like 2 cycle motor cycles etc ? I don't know, I am just asking.

My experience is that if you use a primer the choke is not needed at all.  The primer pumps raw gas into the intake manifold.  I usually pump 4-5 strokes on the primer until I feel good back pressure and know that fuel is going to the manifold.  I open the throttle about half way and start cranking.  When the engine fires it will run for a period of time on this fuel charge....usually enough for the engine to continue to run.  If needed I will pump the primer a few more strokes to keep the engine running while it draws mixture through the carb.  On some of my engines I've removed the enrichener (ie, choke) and filled the hole with a sealant.

The primer and carb enrichment circuit both get the same results by providing a rich mixture to a cold engine but they are different in other ways. The carb enrichment setup will need one or two cables to activate from the cockpit and it also harder to control how much fuel that is needed to prevent flooding. To me the primer is more user friendly and simpler to hook up. I just use 2 pumps then start the engine. If it starts to lag I apply one pump more until the engine sustains idle. Either way they will both work.

Monte

I have used both and prefer the primer circuit.  A couple of squirts to get it to light off then, ease in one or two more once it is running (as needed), then you are all set.

The primers also function as an emergency shut down option (by flooding the engine if you lose your ground), and can be used to operate the engine to some degree (say to a safer landing spot) should your fuel pump fail.

I agree with LSaupe.