Replace thermostat on Briggs & Stratton model series 90000?

I'm a do-it-yourselver - not an expert. Had same problem & I think I figured it out (at least my mower worked after wards). Dunno if it'll work with your engine, but give this a try. Disconnected the spark plug (to prevent accidental start). Put your fingers up under the black "hood", just above where the muffler attaches. You should find a plastic "arm" that you can move left to right (it springs back). This is 1 end of the "Vane-air" mentioned in the parts diagram, which opens & closes the choke. The thermostat arm is also able to be moved back & forth with a spring return. While placing the muffler back in position to be bolted back on, I placed the metal thermostat arm (in the natural position) up under that black hood & in front of the vane-air arm. I then finished bolting the muffler back on & the mower started & I was able to finish the lawn. I hope this helps.

Holly
April 2010