It will start and run but when you go to till it boggs down and quits. There is no float bowl on carb. It has an automatic choke and only one adjustment screw. Any info on how to adjust carb would be helpful.

Bogging down usually isn't an adjustment.

First place I'd look is at the governor. Make sure it easily moves. Spray with carb cleaner.

The carb is a possibility. Usually caused by gas stored in it. The fuel inlet valve gets stuck. You might try to rebuild it.

When you do rebuild it, count the turns of the screw until it bottoms. Probably 1.5 or so and use that as your initial adjustment.

You could try some Seafoam. Motor Treatment - Sea Foam

Make sure you use a fuel system additive like Stabil and remove the fuel before storage.

Your tiller may have a diagram on Parts & Accessories | Shop & Find Lawn & Garden, Appliance Parts at Sears PartsDirect | SearsPartsDirect.com

If the engine is briggs, it will have a model and type number stamped on the blower housing. Check Home - Briggs & Stratton for a diagram.