Originally Posted by buckwheat

Removing only one and not the other plug (2 per cyl) will spark the plug you left in and likely cause an awful fire through the open plug channel with this highly volatile ether based cleaner.

The 113 motor is a derivative of the 112, and although not nearly as robust as the motor it replaced (the 119), it still is revered by many.

I would also certainly look at injectors or leaking exhaust plumes for your ticking.