Small engine - rich or lean

[Squeak n Itch]

Went out to blow about 7" on fresh snow this morning. The Gravely was slowing until I increased gas flow (richer setting on primary needle). I have assumed that a little rich is OK for a small engine but running too lean is bad. Does anyone have any real information or experience?

 

[billbill1]

I have always increased or decreased, whatever it takes to smooth the engine out. Has always worked for me.

 

[Squeak n Itch]

Thanks, sometimes the easiest answers escape me.

 

[RonMar]

For air cooled engines in particular, some of the engine cooling is provided by the fuel. Running too lean will increase the chamber temperature and can possible bring on detonation and severe engine damage. The extreme end of this is a hole melted in the piston top.

This increase in chamber temp also means a hotter piston and more stress on the oil reaching the rings, so a breakdown in lube ocurs and an increase in oil cokeing/carbon formation which increases cylinder wear.

On the other hand too much fuel will weep past the cylinder walls and breakdown the lube oil. But an excessively rich mix usually shows up as black smoke in the exhaust and carbon buildup on the pipe.

IMO, it is best to set the mixture screw slightly on the rich side of best run/peak HP...

 

[dqdave1]

well said; I agree.

 

[bontai_Joe]

For an engine that's gonna see a high load consistantly, a little rich will keep the engine power up. You may even notice a slight surging in an engine set up a little rich with no load that smoothes out under load, and I would consider snowblowing a high load application.