05-01-16, 02:42 PM
It's possible that you're getting a bit of carb icing.
The heater circuit that circulates warm coolant through the carbs can get blocked (or may just not be effective enough when the engine's running without a load).
If you don't want to take it out for a proper run I'd do as Ruby Racing suggests… ten minutes idling/annoying the neighbours isn't going to get the oil up to temperature anyway.