Out of curiosity what did you set the valves to? a bit of research online is telling me that valve clearance is critical on these. I do vaguely remember having a similar problem with one but was many years ago. According to the manual it should be a very tight .004" on both intake and exhaust
Tecumseh shut down production in 2009, and yeah unlike briggs and honda aftermarket has so far not really gone anywhere. We struggled to get genuine parts 10 years ago.
I am not a big fan of the tecumseh engines at the best of times
