I think the first digit of the serial number on Tecumseh engines made before 2004 dictate the year the engine was made if I'm not mistaken. In your case the first digit is 9. You still have to estimate the decade but through some common sense it's not that hard to narrow down. This being said, your engine would have been produced in "69","79","89" or "99". Well using the common sense method, we know it's not a "69", the
bike is obviously newer than that. We also know that it isn't an "89" as I don't think Ruttman's were still being made then, not to mention I think the recoil is different on the 80's and up models. That narrows it down to "79" which makes a little more sense, heck, I didn't know they were still made past '76-'77, really nice
bike by the way.