Garden tractor pro electric clutch

I have an old snapper lawn tractor with an 18 hp Briggs and Stratton I/C horizontal crankshaft, horizontally opposed engine. When I bought it the old clutch lead wire was broken off from the magnet windings. I was able to solder it on and it worked for a while. Then it broke loose again. This time I was not able to fix it. I went to the shelf and got one that had been on a 16 hp K341 Kohler. I had to get an adapter sleeve to make it fit the smaller crankshaft. Yesterday I mounted the clutch. The old one was a three hole mount, and this one is a 4 hole mount. The holes were extras in the block so it was fairly simple to mount. When I put the power to the clutch, you can hear it snap into engagement. When I grab the pulley, you can feel some resistance to slippage. It does not seem like enough. I looked at horsepower and torque formulas and it says 18 horsepower at 3600 rpm should be 26.3 ft pounds of torque. I am pretty sure there is not that much resistance. I haven't rigged up anything to test it with a torque wrench. The pulley on this one is larger so I have to buy another longer belt to actually test it with the mower deck. There does not seem to be any adjustment on the clutch. It was original equipment on a 1972 Allis Chalmers 416. I have a newer clutch on a Cub Cadet 682 that is similar or the same as the one that quit. If all else fails I guess I can rob the one from the Cub. It does have three springs and adjusting nuts. Could there fail to be an adjusting means for this style clutch, or am I missing something? Thanks in advance. I will be on the road during the week so will report progress or lack of it as time goes on. Same machine but different problem, I spent a good part of yesterday pulling the engine to replace the starter pinion gear. Evidently the factory engineers don't want anyone to work on these as it was not a pleasant job, but I did get it out and replaced.

Those have an adjustable air gap.
Look up and watch the YouTube video.
If that doesn't work, check it with a multimeter.
Make sure it gets 12 volts when it's turned on.