Dolmar 5100
1.5 years old - 1 gallon of gas old (not used much)
Opti 2 oil mix with stabilizer
sparkplug has spark
starter rope pulls, feel compression, but no combustion

Before dying it was running fine.. then suddenly stopped and would not
start again. In the past is has done similar, but always restarted
later -- almost like there was some sort of overheat/overload
threshold.

The last fill of gas was from the 1 gallon container of gas that was
bought 1.5 years ago (and mixed with the 1 gallon Opti 2 mix pouch)

When I pulled off the air filter, it seems there is more dust "inside"
the filter than I would expect -- but I would expect no "visible"
dust, and there is a film along the inside of the filter.

Looking for troubleshooting ideas.

Thanks