That is exactly the bump in the road...

But I decided to go the analog McGyver way and solved it like that.

The challenge I had was that a glow carb from an AP .06 Wasp (1 cc glow engine) had to supply an ASP 30FS running at 1500 RPM, fixed RPM variable load.
Since RPM is fixed by governor, increasing load actually DOES force the governor to open the throttle, but since the RPM does not rise, that means carb vacuum and thus fuel draw reduces.
It is the same effect that forces us to use a servo-slowdown when opening the throttle, only, in my case the RPM won't come up.

So I was having an engine that went from slobbering rich at low load to too lean at high load at constant RPM (meaning you cannot really determine what is going on by ear).

Given the very low RPM, very low fuel consumption (this thing, even slobbering rich, only consumes less than 1 oz of fuel per hour), there also is no visible smoke plume to go by...

What I did, was attach about 1 1/4" length of 1/8" OD Brass tubing in front of the air intake, that serves as a restrictor.
At low load (throttle barely a pinhole sized opening) the throttle barrel is the main restriction, at increasing load the throttle opens, the airflow increases and the Brass tube becomes the dominant restriction, shigfting the vacuum area to in front of the carb barrel, increasing fuel draw at increasing load.

I can tailor that vacuum bias by varying the length of that Brass tubing, and at the moment I am (based on sparkk plug colour) probably just ever so slightly on the rich side at high loads.

It looks rather improvised (and that is because it IS improvised), but this is that restrictor.


So far, it works like a charm, the engine is running pretty consistent and so far absolutely reliable, it starts really easy, and the only "thing" procedure-wise is that you have to start it on manual throttle, and once running you need to bring RPM to within a certain range close to set RPM or the governor won't engage. Without a visible tach, that is a bit of a trial and error thing, but no big deal. Once the governor engages, it basically runs until the tank is empty.

Cooling is done by a tiny 42 mm electric fan, and more as a gimmick than anything else I added a commercially availlable themperature controller (very cheap Proportional controller, nothing fancy) and changed the NTC resistor for a FrSky probe, which conveniently brought the regulating range to 70~100 deg C.

The weird thing about this cooling is, that when I ran the engine without cooling, it never got over 110 deg C as far as I can tell, and the other ASP 30FS I have runs way hotter.
I do not believe for one minuten that this tiny fan has any significant effect on engine temperature, because even an idling prop generates a 100 times more air movement, but alas, without the fan the engine refused to run reliable, and needed a belching rich mixture (judging by the pitch black exhaust residue) while using that tiny fan, I'm now fairly close to Stoichiometric: the exhaust residue now is a light grey oil/water emulsion and the tailpipe does barely get over 30 deg C.

Haven't been able yet to determine engine temperatures due to the shrouding on the fan (no access for IR temp gun).

But who cares if it appears to run right all day long, right?