What I have experienced using the recommended APS fuel pump: My Moki 180 has been difficult to start since day one. Going against almost all past practices, I skipped any bench running and installed the new engine into my aircraft.
After two very frustrating rounds of coil replacements (see my earlier post), I finally have a reliable ignition. However, starting the engine continued to be difficult, despite my 20 years history of gas engine success (incl. Moki 250 and Saito radials) and over 40 year history of model engine experience (incl. glow radials).
And I have to say, it is unfortunate I always feel compelled to "qualify" my experience, but I assure you, I am not some model engine nitwit who immediately blames the product when I run into difficulties - quite the opposite.
The last time I flew my CARF SU-31 at an event, I posted one flight. An hour later when trying to start the engine again, no dice. After one "burp" while choked, I could never get it to even pop. Everything checked out fine and I had no interest in wrenching on the plane at the event.
The following morning, I removed the spark plugs and found the bottom two literally with pools of fuel in them. I had followed the exact same starting procedure as always - the exact same starting procedure I have used on every gasser I have ever owned, including my Moki 250 (which did NOT an external fuel pump).
After drying the plugs and swapping 1 and 2 with 3 and 4, the engine started normally and ran fine.
I have since sold the airframe to a buddy and removed the 180 with its next home being an F8F Bearcat. To that end, I mounted the Moki on my test stand and ran it with a 4 blade prop and no fuel pump.
VOILA!
Now it starts with the exact same reliability as all my other gassers, using exactly the same starting routine.
With no external fuel pump, I did have to adjust the H and L speed needles, but engine starting is now 100% reliable, hot or cold. It throttles well and runs like a top. Also, I notice absolutely NO difference in the way the engine idles, throttles, or howls at full throttle without the auxiliary fuel pump.
Clearly,
the APS fuel pump was FLOODING the engine.
OK, so mine is the programmable version and I never slaved it to the throttle stick. IF at some point in the future I decide I need it, I will.
After probably 20 flights on the engine
with the fuel pump, combined with MANY sore arms starting the Moki, I have NO intention of installing the fuel pump into the Bearcat.
After a dozen or so bench runs there is absolutely zero residue/blockage in the air pulse pump line which actuates the internal Walbro pump diaphragm.
With my Moki 250 I did have to keep an eye on that line and clean it out perhaps every half dozen flights. The same diligence will be exercised again.
No pump vastly simplifies engine/tank installation too.
While I am NOT saying the APS pump is a bad idea, I am just describing my experience with it. Chances are, had I slaved it to the throttle channel, this starting/flooding problem may have been avoided.
BUT, I prefer what has proven to WORK for ME over the years, combined with simplicity, even if it requires extra diligence in keeping the engine's internal pump system at 100%.