Well, on an air bleed TT.42, it most definatly will cause issues if the tank is set low in the plane, you see, I don't have a low speed needle to adjust the flow rate, and at idle the pressure feed is lowered due to the lower rpms of the engine. So at idle it runs hot to the point where if you pinch the fuel line it dies instantly, so if I tune it to peak rpm and back off about 300 -400 rpms to keep it rich, I can sustain an idle but not for more than 3 minutes before it loads up, if I open the airbleed it will idle too high and I almost have to shut the carb off to make it idle. Now the transition is alright but sluggish, it just seems to have a fine line your walking on with a single needle carb. Yes they are simple, when your not trying to suck fuel up to the carb, it will much rather pull the air from the airbleed than the fuel from below. I actually have many years tuning engines on models aircraft, cars, boats and being an ex automotive tech, I'm pretty good at tuning engines. But there are many things that can give a problem in an engine, bad fuel, plug, lean, rich, worn, low compression, high compression,excessive dirt, air leaks, loose componets, missing componets(head gaskets) and even the freakin stripped screw will cause an air leak, especially if it's used to hold the carb on, if you can't seat the head tightly, then it's going to pull excess air into it. Over the years, I've had maybe 12 supertigre's and only 1 was an odd runner, but that was to an slight airleak in the brass needle plate on the carb, simple fix, new oring lubed in dielectric grease and installed in a clean carb body. TT are good engines, but most ABC or ABN engines don't tolerate lean running, but that goes for every engine out there as well.