When everything is clean and working properly a small spray of fuel will spray from the port when you push the primer. Your high speed needle adjustment at 1 1/2 turns from gently seated is unusual. As you stated 3/4 to 5/8 is more of an average adjustment, but every carburetor/needle combination is unique. The sneezing is a sure sign of a lean condition. Have you tried richening the low speed needle? nadmd mentioned that the adjustments are very dependent on each other, so an adjustment to the high speed needle requires an adjustment to the low speed needle. Is the entire fuel system clean from the tank and tank filter, right down to the check valve and low speed fuel supply line?
Regarding the compression numbers, as LLoyd stated the 67-70 PSI is on the low side for this model. I owned a TD-20 that I put a ton of time into and could never get it to idle. The top end power wasn’t good either. That motor had 70 PSI on both cylinders. I finally blamed the problem on low crankcase compression from excessive wear. After a different powerhead was installed, that motor ran strong and idled down very nicely. The replacement powerhead had approximately 72-73 PSI compression.
It’s definitely worth looking into fuel supply/adjustment issues before concluding that the powerhead needs a replacement. Hope you figure it out.
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