Why not look for a used motor on craigslist. I found hp ratings from 12 to 18 twin for $30-50. Bolt pattern is the same and an easy switch. Of coarse you can also pay a lot more.

might try poking around here for a model#.. Here is a link that might be useful: older sears riding mowers

@williamgfv Glad to help, but would appreciate if you would at least do basic research first. Google 917271910 and results will show "Sears Parts Direct" with info on this tractor. Third listing shows PNG's of electrical diagram and link to PDF of complete manual, which includes diagrams and parts lists. I've also included links directly to manual PDF. www.managemylife.com/mmh/pd_download/lis_pdf/OWNM/L0203208.pdf

You say "The engine ran smooth etc." And WHEN was the last time that engine RAN smooth" 2 days prior to swapping? Or, last year? You really ought to start a new thread to cover this issue. It might be helpful to some of us if you will provide the engine model number and type number you find stamped or listed on a decal ON THE ENGINE. And you need to give the numbers for both engines and tell us which one you took out and which one is the replacement. What about the fuel hoses you are using? Are they new? If the Yardman tractor had sat for a long time in an inoperable condition, the inevitable varnish that will form inside the hoses may be breaking loose and migrating into the carb.