I think we have moved forward, Paul. Those settings seem to be telling us that the idle system has been blocked for quite a while, and someone has tried to compensate by opening up the screws. I suggest you begin by verifying the model number. Do this before you physically attack the carburetor. Here is where the numbers are located:

[Linked Image]

You have said that the type number is C1T, but let's be sure about that before we pick up the oxy torch.

The next step is reading the overhaul manual, which you can download (free) here:

http://www.lawnmowerpros.com/Shop/Zama/TechguideCC.pdf

You need to go through the overhaul procedure, as laid out in detail in that manual, for your model carburetor (probably C1). Note that from the symptoms, including the Stillson marks on the screws, you probably have a clogged idle port and channel, but we can hope that the obstruction will blow out with a strong blast or two from the carburetor cleaner can, using the long tube (supplied with the can) attached to the nozzle. Do not remove the Welch plug unless this process fails - see page 3 of the manual.

You may find you need to install a rebuild kit, when you get into the details shown in the manual. (You certainly will if you have to remove the Welch plug, of course.) Also, when you come to adjusting the mixture screws, you might try a trick others sometimes seem to use, with moderate success. Find a piece of thermoplastic tubing with an ID about the same as the root diameter of the splines on the screws, heat it up, push it over one of the screws, and let it cool. Then you hopefully will have a tool for making the adjustments. Depending on the quality and wall thickness of the plastic tubing, it may last for years, or it may die during this current project, but you can always cut off the last quarter inch of tubing, heat it up again, and proceed from there.