D-19 carburetor on the One-Seventy high-deck

Worked this week cleaning parts from four old carbs to build one like what's on a D-19 and fabbing up the throttle and choke linkages to work on a different engine. Replaced the One-Seventy Zenith brand carb with a Marvel-Schebler TSX-848.  Went to my favorite dyno today hoping for 60 HP at the PTO.  Did not make any runs with the original carb for comparison and this tractor has an engine that I'm guessing has 3 to 4,000 hrs on it. Runs good. Doesn't smoke blue at all and rear main seal drips. Anyway, by Nebraska Test numbers the 175 gas makes 56 HP @ 1622 engine RPM ( 540 PTO speed) and almost 61 HP @ 1800 RPM.   We came in spot on at 56 HP at PTO speed, but as the RPM's were increased we were a little short.  At 1800 RPM we had 58 HP. At 2,000 RPM we scored right at 59 HP and at 2100 RPM 59.5 HP.  So, it seems to me that the different camshaft grind is hurting our performance. The 175 cam grind gives about .075" more lift at all valves.  The D-19 carb has a 1 inch venturi hole, which is the same size as an actual 175 carb. The D-19 carb has an 1 5/16" throttle butterfly, while the 175 is 1 1/4" I believe. I was in hopes this difference would make up for the camshaft improvement. Anyway, we've for sure gained HP from a One-Seventy tractor.  51 HP to 56 HP at 540 PTO speed and 54 to 58 HP at 1800 RPM rated speed. Anytime you can gain 10%, I guess that is a good day. Got some pics on my phone and will try to post them when one of my grandkids can help.

Maybe for a 4000 RPM engine, but with that center-fire spark plug and power crater piston, I doubt it. I have tried things like that on my stock RPM pulling tractor over the years and nothing ever really made any difference over a good condition stock ignition system. There is a reason AC had a different camshaft in the 175 (and original One-Eighty gas) engine and I think I found out why. It's just amazing how (on a 175) you can go from 1622 to 1800 RPM and gain 5 HP, and on my tractor with a similar sized D-19 carb, I gain only 2 HP. All part of the fun of changing/improving things !! I know 10% more is good. I was just hoping for 12%.

something tell me the good Dr. will be doing something else. :)

Intake manifold throat opening actually matches the D-19 carb with no grinding. Manifolds throat size has always been larger diameter than a standard D-17/WD45/170 throttle butterfly plate. The D-19 carb has a lot of overhang to the mounting flange that I chose not to grind away.