Ok lets start by stating MY biases. I don't like Nitro for sport engines Generally I like to use FAI fuel (80% methanol and 20% castor oil) I will go up to 15% nitro as some sport racing rules spec this fuel. Now some of the design from the 80's and earlier engines for the USA market do run better with nitro as high as 25%. These can be identified as the heads often don't have much of a squish band. To aid idling I often like to add 3% to 5% acetone rather than nitro.
I don't like any synthetic in the old lapped P&Ls. I've seen these synthetic act as a varnish remover damaging the base compression seal on used well broken in engines. To this day 100% castor oil is still the best for the leaded liner with lapped cast iron piston.
The airbleed is NOT there to effect a change in the stoichiometric mixture balance, well not directly. The purpose of the airbleed is to bleed most of the idle air under the spray bar so that this air does not pick up fuel from the spray bar. (See Bernoulli pressure drop as a function of flow). In
post 16 you can see where Super Tiger messed up on the air bleed for the 1965 ST23. The original air bleed was too high up in the carb throat as it allowed the "bleed " air to flow past the spray bar picking up fuel (causing a pressure drop). I drilled a new real bleed port to allow air to bleed under the spray bar. This air did not contribute to the pressure drop. Air bleed carbs have poor fuel flow at idle. It is this poor fuel draw that limits the fuel flow at idle. (Truth be told poor fuel draw is just what we don't want at idle! The auto mixture carb allows all the air flowing at idle to aid in the drawing of fuel). A big influence on idle performance with an air bleed carb is the tank placement. IF YOU CAN'T GET THE MIXTURE LEAN ENOUGH TRY LOWERING THE TANK.
I also don't like the 10x6 prop on sport 0.40 CID (6.5cc engines). With rare exception I find a marked improvement in airframe performance dropping down to a 9x6, 9x7 prop. Occasionally even a 10x5 will out perform the 10x6 on large winged trainers. This is because the engine really is just a heat pump. Allowing the engine to spin up will allow the carb to draw more air at full power. This will result in a stronger pressure drop across the spray bar. To keep the mixture in balance you will need to lean the high end mixture. This lean mixture will be in effect through out the full throttle range with an airbleed carb. A big plus with a faster spinning engine is that your pitch speed will go up. You will need more speed at altitude to lift the same airframe weight. So think about trading some static thrust for real air speed by going down on the diameter of the prop and going up on the pitch.
As to the glow plug I forget how Enya spec'd their plugs. But I like to use the glow plugs with the higher platinum content. These were usually labeled as cold for high nitro engines. The reason nitro engines need more platinum, is that it is the catalytic reaction between the methanol and platinum that helps combine the oxygen. In high nitro fuel the nitro displaces the methanol making it more difficult for this catalytic reaction hence the need for more platinum.
Ok to your issues. I too find it odd that you can't get a leaning response. Make sure your bleed port is in fact clear. The use of castor oil fuel can leave old oil blocking the bleed port. As it is the pressure differential between the tank vent and the carb spray bar that draws the fuel into the engine. With less air pressure at altitude the fuel should flow less. As to the glow plug question, does the engine run better at full power with the glow plug lit. If so you need to advance the timing with a hotter plug (one with more platinum) or less head clearance.
I don't recall if your Enyas have head gaskets. If they do try to remove 0.1mm to 0.15mm (0.004" to 0.006") worth. This is to aid timing and combustion.
Don't drill new or larger air bleeds. The Enya carb was of a good working design. Now Enya and others did have a true auto-mixture carbs with an airbleed adjust to fine tune the mid range on their higher end engines.
And last try some fresh fuel. Older fuel often doesn't have as much methanol as it use to.
If none of this helps we can go deeper into the combustion process.
As to engines I LOVE the Super Tiger with the MAG V carb. I hate the OS FP & LA with their air bleeds and poor nickel P&Ls.
I don't think changing the airbleed to a Perry will help much. Yes, the Perry is a much better carb than the airbleed. By the way, the latter K&B carb is not of the same design as the Perry. The Perry is a slot over hole design. The K&B uses a comma shaped metering port. The Perry is prone running rich in the mid range the K&B is much better in the mid range.
Mecoa is a vendor that often tries to keep these old machines running with new replacement parts.
