I've got an RCS 140 that I've run several tanks thru it on the bench . I had the engine mounted upright and it ran just fine. Now I've mounted it inside the plane, inverted, and it doesn't want to start as easy, nor idle. I've found that if I keep a little choke on, it will idle , but still has a tendency to want to cut off, and will die immediately if I turn off the choke. I'm running same fuel, and tank. I have installed a tee inline with carb and clunk for filling the tank. I have the same vent as before. I have not adjusted the needles any since it was run on the bench. I'm running large tygon fuel tubing, large tee, and large brass tubing in the tank. I have added a large Sullivan crap trap filter inline also.
My question is do I have a mixture problem? Since this is a walbro carb, which is pumped, shouldn't it remain the same whether it is mounted upright or inverted? And should I have to tweak the needles any? Does it sound like it's too lean on low needle? Any help is appreciated.

PS- newbie on gas engines!