Great success today. I changed out both belts. I also leveled the deck, though the front to rear is not quite correct. They want the front of the center blade 1/4" higher off the ground than the rear of the side blades. They are about level now.
There is a design flaw with the machine and that is the transport lift mechanism. With it lifted, if you forget and engage the blades, the belt will drag on some linkages. The lift is useful because the rollers at the back slam into stuff (my yard really sucks) and it helps to lift it when moving around the yard. So I'll try to remember. I did scorch my new belt but I think it is alright. I might tighten the adjustment.
As far as the carb issue goes, it still seems to be fixed. I mowed and even hooked up the big vacuum thing with the bagger. Not once did it sputter or blow black smoke. So that is a relief. I left the fuel level at a little under 1/2 so we'll see if it still drains out. If it does, there's probably a tank issue because the fuel pump and carb should be good now. If it doesn't leak, I may still change the oil again. Or not.
While I had the deck off, I removed and sharpened the blades on my grinding wheel. The blades look like high lift to me.
By the way, the blower thing is unbelievable. It moves so much air. I think it will be awesome for leaves in the fall. Wish it had a triple bagger. Also, I need to fashion some kind of handle to the bottom of the bags but they did work.
Overall this was a great day and it mowed flawlessly. The transmission and engine worked well. That was the goal.
Pics.
The machine sans deck. If you look close, you can see Ackermann steering geometry.
The old deck belt was pretty destroyed.
Deck with the new belt.
Turbo collector including upside down part number for future reference.