OK - I did try to get the primer bulb 2 years ago. IIRC, the serial number was not readable. I'll check again tomorrow.
The engine model is Tecumseh WTPXS-1851BA Again, IIRC, my engne model was actually WTPXS-165BA. But the 165 wasn't listed on any Tecumseh site. So I was using the 185...