"Space Cowboy" wrote in message
om...
Hi all,

I have a 20hp MtD Lawn Machine Riding tractor and my elevation is 6000
ft. I pull the choke(close) and its starts on the first or second
crank. When I push the choke(open) after warming up I get a surging
rough idle. If I pull the choke about a quarter closed the rough idle
goes away and the engine sounds fine. Is this normal operation for a
tractor at elevation ie enriched fuel mixture?

Thanks,
Jim

Yes, what you need to do is adjust the air\fuel mixture so it runs smoothly
with the choke in fully.