@baddeal I wonder if the motorcycle tire did not throw off your timing. How did you check it? what exact engine is your Tecumseh? Something like a Enduro Ohv17 etc. Most Tecumseh ignition module depend on the flywheel key for a proper ignition timing. By your running over the tire, it is possible that this partially sheared the key, which will offset your timing. I would definitely take a look at that and replace the key.
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=== Update (08/06/23) ===
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@baddeal I just received this [document|31490]. It is engine specific. See if that gets you a bit closer.
@baddeal I wonder if the motorcycle tire did not throw off your timing. How did you check it? what exact engine is your Tecumseh? Something like a Enduro Ohv17 etc. Most Tecumseh ignition module depend on the flywheel key for a proper ignition timing. By your running over the tire, it is possible that this partially sheared the key, which will offset your timing. I would definitely take a look at that and replace the key.