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Discussion Starter #1
:wave:

Howdy... new member here looking for some advice about a Briggs vertical shaft 675 engine on a Snapper walk-behind mower. I've got two minor issues that I'm trying to work out.

1 - I noticed that the plastic cover above the front-wheel-drive belt is beginning to melt right underneath the muffler. The muffler is not making contact with the plastic and there's about a two inch gap between the bottom of the muffler and the plastic.I suspected that the gaskets between the muffler, choke thermostat and block were leaking hot gasses onto the plastic, so I replaced the gaskets... no luck. It still seems to be too hot. Should my next step be to replace the muffler?

2 - Semi-related, I've noticed that the engine has become increasingly hard to start when warm. It seems the choke thermostat (mounted between the block and the muffler) keeps the choke plate in the wide open position even after the engine cools for a few minutes. When the choke is open in this state, the engine is tough to start and can take ten to twenty pulls. The immediate fix is to manually push the choke actuator rod to close the choke a bit, then it always fires right up. I know that the thermostat is working because when the engine is stone cold it returns the choke to the fully closed position.

So...

I guess my question is: is it possible that this muffler is just plain running too hot and causing both problems? Should I check to see if I can get the eninge to run a bit more rich (thereby hopefully a bit cooler)? Or should I replace this muffler?

Any advice greatly appriciated... I obviously know just enough to be dangerous but don't have enough experience to know what to do next.

Thanks!

-Tom
 

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Discussion Starter #3
Update:

I replaced the thermostat (part of the ReadyStart "feature"). It's behavior is exactly as before and I think it's by design. I don't know exactly what the cutoff temperature is, but if the engine is warm then the choke is fully opened by the thermostat. It takes roughly 7 to 15 minutes for it to cool enough to the point where the choke starts to close a bit, then it starts right up. The new thermostat behaves exactly like the old one.

It also still starts if I manually hold the choke closed a bit when still hot.

I don't think it's a valve issue... it starts and runs fine when given a bit of choke and still hot. I guess I could rig up a manual way of applying the choke and ditching the thermostat, but boy that sure defeats the purpose of buying this new lawnmower just last season.
 
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