I'm thinking about replacing what's there with a uniflow, that isn't so tall. I would hope that'll give me better draw and put outboard edge of the tank closer to the needle. I have a bit of an issue with that because I'd like to be able to do the pattern with the plane, and there's only 3 1/2" from the leading edge to the back of the engine. This leaves me concerned that any tank that'll fit will have problems with fuel flow toward the end of the pattern.
Just make the tank depth/vertical dimension whatever is needed to get the desired capacity. I agree with the general idea.
Check that the insert is in the venturi. It should be a black oxide-finished insert about 3/8-1/2" long , fit the inside bore of the venturi boss, and maybe a 1/32-.040 wall thickness. The spraybar passes through it, so it's way down in there. They are frequently removed to Get More Power. The apparent power level and extreme mixture change from beginning to end is strongly suggestive that this is not present. If it is present, you can make it smaller, by sleeving it down with brass tubing. That will make a big change in this case, but, you have way more power than you need, and not enough suction, and that would improve both.
15% sounds OK, and may be the only thing making it possible to needle with the excess venturi.
BTW, uniflow will not make it worse, but it also won't improve it. The fuel pressure will be the same as it is at the end of the tank with the current setup, just for the whole flight.
I'm kinda thinking about putting said uniflow tank on the inboard side, but that's not very old-timey.
You want it old-timey, or actually-worky? Also not a bad idea, but it *should* work with a slightly narrower tank as it is, if the engine is right.
I don't think there is a lot you can do about the vibration, slowing it down might move it out of resonance, but without extreme measures you are going to have a lot of trouble trying to fight the resonance by beefing it up.
Brett
p.s. by "extreme measures" I mean stripping the front end down to the balsa and motor mounts, and replacing the doublers with 1/8 hard ply all the way back or beyond the high point of the wing, then rebuilding it. If you even attempt that - which I don't recommend - you will likely find it oil-soaked in all the critical spots, which will be nearly impossible to remove sufficiently to glue on new doublers. Then - you are cutting off the entire nose, making a new one, and grafting it on. And it might not work anyway.
My suggested solution is obvious, but even less old-timey.