It does sound like it's too rich . Have you checked the timing ?
For most motors , 73# is not enough compression to run correctly .
Running a single ring is not your problem , unless that ring is too worn and/or the gap is too great .
I am running a single ring in my FA50 double ring piston . The motor starts easily . Runs smoothly and does it's 'normal' 30 MPH top speed . But , take off is a bit 'less' .
There are plenty of single ring pistons .
Before you buy anything , pull the top end apart and measure what you have .
Piston to cylinder clearance ; ring end gap ( in the cylinder should be as little as .008" and definitely no more than about .014" - .016" ) .