I got the bigger carb today. HDA 137. I opened up the intake manifold to match the new larger carb. The venturi on this one is 16.61mm. Before I was running a WT-542 (13.49mm). I had little time tonight to mess with it. Before I was getting:

Bambula 22x8 7200 rpm It pulls 21-pounds on a spring scale tied to the tail
TBM 21x8 6800 rpm 23-pounds
top flight 20x10 20-pounds

Now it is spinning a MENS 22x10 at 6700
and a Vess 22A at 7000

The MENS calculates to #30 thrust, ...that would be more! nice .

I'll play more and see how it goes. I need to try the old props and see a direct comparison. I just grabbed the closest ones tonight.

Saturday AM:
Mens 22x10 6600 27#
TBM 21x8 7000 24#
BAM 21x8 7450 24#
BAM 22x8 7500 26# (must have been carb setting changed?)
MENS 24x10 5600 28#

For fun I tried my CS-510 conversion with a WT-542 carb, MENS 22x10, 6200.

On the 650... the larger carb does not idle as smoothly as the wt-542. I can not get it to run well below 1800 rpm. That means the plane will roll at low throttle. It seems to have the rich mid throttle issue. If I set the high speed to peak then chase the burble down wiht the low speed needle, I end up lean at the low end. Isn't there something about filing a notch in the butterfly to help that? I am not sure it is worth the bother, I only gained 300 RPM with this exersize.

Later Saturday, BBQing some pork and drinking beer. Why not fuss around in the shop? I made an exhaust with two 1" pipes. Free flowing exhaust is crazy loud! It now spins a Bambua 22x8 at 8000. That is 6.6 hp and 41 pounds of static thrust. It 's almost like a big boy engine. So, I have gained 800 rpm over where I started.

I will fly it tomorow.