Can anybody post the effects that adjusting one needle has on the other ? EG: Leaning the low end will cause the high end to be a little ____.

The needles interact to a point..
If the high speed needle is already too lean from the low needle being too rich, leaning the low needle will adversely affect the high speed needle...A Walbro will run with the low needle way too rich if the high speed needle is almost closed, been there...
If the high speed needle is correctly adjusted the low speed needle will have very little effect on the high speed needle..Correct adjustment of the high speed needle is a few hundred rpm short of the highest rpm...
If you start with both needles open 2 turns and set the high needle first there will be no adverse effect from leaning the low speed needle...The low speed needle is correct when the transition from idle is good, just richer from the point where the engine dies when the throttle is opened...
You can NOT harm the engine adjusting the needles on the ground...If you get the high speed too lean the engine will just die...If too rich it will blubber and not run as fast as it should...

So am I understanding you correctly that it is difficult to set the low end too lean because anything leaner than the optimal setting will result in the engine shutting off when the stick is advanced? I am having a little trouble figuring out my engine.

I am getting blubbering primarily after a downline. This would indicate a rich low end? I do not have any sagging on the upline.

When you have the low too lean it will want to die when you advance the throttle fast. Keep richening it up till it doesn't plus a tad and that should be about right. I basically just repeated what Ralph had said. Then I ALWAYS reset the high after I touch the low.

Any burbling (4 stoking) is an indication of a very rich condition. I usually set my planes so there is an ever so slight burble (barely detectable) in level flight but it clears when pulling hard in an up-line. Then when winter comes and the 100+ degrees go away I let them run a little leaner.

Oh by the way crash have you look at your plugs, they can tell you a lot too.

RCIGN1
I'll post more later with particulars; problem unit is an Echo 21cc with 167 Walbro. Pulled first carb off could get it to run after cleaning. Second new carb is turning APC 17-6 6000 @ hallf of butterfly opening and crapping out with any further advance of throttle. If I restrict the air intake (richen) I get pick up in RPM? Don't have a smaller size carb to substitute. Are you aware of any of the 9.53 Walbro that have enough of a protruding shaft on side opposite factory linkage setup? (Like the 167-1 carb)
Too late.....

Thanks guys. I think the problem I had was that the high end was too rich. When I leaned the low end it made the transition even worse so I richened the low end again to get the transition as smooth as possible. The whole time I was too rich. I am close now so I will begin turning the low end in until I get it right. Thanks again.

Mikenlapaz..To get a longer end for the linkage to the sensor ring on my conversions
I take the shaft out of the HDA and SDC series carbs and turn it end for end...Some carbs are made so this won't work because of the location of the flat in the center...These can be used by soldering a short brass tube on the short end, then making an arm from 1/16 sheet brass...I did this on all the WT carbs on G26 conversion engines until I found a molded arm with a setscrew, made especially for these carbs by Bruce Hanson...
The WA167 works good on a G23, must be another problem, maybe the carb is opening the wrong way...The disc should progressively uncover the small holes in the venturi when opened..

Key piece of info regarding H/L needles:

The 'L' screw supplies fuel from idle all the way to full throttle. The 'H' screw supplies fuel ONLY from midrange to full throttle. So at WOT, the fuel into the engine is actually the sum of the H and L screw settings.

What does this mean? It means that adjusting the 'L' needle has an effect at all speeds.

So technically, when you lean the low needle you would want to richen the high to compensate?

The low needle will not affect the high if both are set correctly...If you're not open at least a turn on the high the low is probably too rich....
That's why I always start 2 turns open on both and set the high first, then the low, then re check the high...Works every time on every gas carb....

Thats exactly what I did..opened both 2 turns adjusted the low and the high was perfect..