Geoff,
Ideal temp and humidity for ice but I'm leaning toward Nick's suspicion. 800f seems a bit low for 3000RPM. What is the needle clip setting on the jet needle and what is your field altitude?
If you have a primer or if you have an enrichener (choke), set the RPMs at 3000 and give the carb a shot of fuel with the primer or choke. If it runs better, the jet needle may be set too lean. If it begins to die, It may be too rich.
What is your max. RPM temp?
Bill.
