Krayxc, I'm no expert by any means, but I do have some procedures that have worked for me. One thing I have noticed about most model airplane gas twins is that the carburetor does not meter fuel well at all throttle settings. We're using carbs that see duty on chain saws and weed eaters, and those applications only require a decent idle, and a decent full throttle. Most giant scale plane flying is at part throttle, where the carb doesn't do well. We're forced to compromise and this is why one usually hears a big twin that idles well, and pulls well at full throttle, but exhibits a slight burble a part throttle settings. We need a richer than required setting at part throttle to insure enough fuel at full throttle. I have heard big twins that were smooth and leaned down enough so they didn't burble at part throttle, but, for the most part these engines also didn't pull as well, sagged slightly on uplines, and ran a bit hotter that other engines.

The next thing I've noticed is a difference in tuning glow and gas. On glow engines the low speed needle is only effective up to almost 3/4 throttle during which the high speed needle setting makes no difference. The high speed glow needle takes over at 3/4 to full throttle, during which the low speed needle setting makes no difference. On the other hand, a gas motor with a Walbro carb has a high speed needle that starts to be effective at less than 1/4 throttle, and the low speed needle is effective at ALL throttle settings. Any change you make to the low needle setting affects the engine at all throttle settings. The Tillotsen carbs that some 3W engines use does a better job at part throttle settings but even it is not perfect.

Armed with those facts, the way that I tune my carb is to first understand that the so-called "factory" settings are not the ideal settings for the engine, rather are simply settings that will allow the engine to at least start up and run. The best settings take into account your region's temperature and humidity, altitude, prop choice, airplane characteristics relative to speed, drag, etc. You must listen to the engine tell you what it wants.

Starting at the factory settings, turn the high speed needle to peak rpm at full throttle, then richen to a 200 rpm drop (maybe 1/8th to 1/4 turn richer on the high speed needle). Now, after revving the engine up to clear it out, throttle to idle and adjust your low throttle trim to get a low idle, say 1,700 rpm. After 10 seconds quickly advance the throttle. If it burbled briefly and then cleared out, you know it's rich, so you lean the idle needle 1/8th turn, rev it up to clear it out, and try again. The rev it up and clear it out part is impoortant, because if you don't it fouls the next test. After several "tests", you'll reach a point where the burble is less and less, and you'll need to lean the needle in 1/16th turns rather than 1/8th turn. The idle needle is very sensitive as it gets close, and it's easy to over shoot the mark. You'll know you've gone too far when you advance the throttle and it doesn't burble, rather it hesitates kinda gasping for air, then revs up. You then richen the idle needle in 1/16th turn increments, until you get the stable idle you want, and the transition response you want when you open the throttle. You then check your full throttle again, because leaning out the low speed needle also leaned out the full throttle. You adjust the high speed needle to get the full throttle peak, then richen the high speed needle a bit more so that the full throttle rpm drops 100-200 rpm. Go back and check the transition and adjust the low or high speed needle to suit.

All this is time consuming since you can't make the adjustments with the engine running, rather you've gotta run a test, stop the engine, adjust, fire it back up, CLEAR IT OUT, then run another test. As you can see, just like in a glow engine, the MAJORITY of time is spent adjusting the low speed needle, and you listen to the engine tell you what it wants. The above assume that the engine was rich at the first test. Obviously if it's too lean, you open things up until it IS too rich, then creep up on the proper leaner setting. If the low speed needle needs to be opened up more than maybe 1.5 turns to get an idle, I'd look for an air leak somewhere. BTW, I'm assuming you're using the stock mufflers, right?

I'm sure nothing I've said is new to you, and on the top end, your engine is turning about the same 6,300+ rpm my 102 pulled with the Menz 26x10, if memory serves me well. Hopefully, that idle will come on in for you.