A C150 pilot reported they experienced a rough running engine so diverted to a nearby private airport.

Narrative

Made a precautionary landing at private field ZZZ without prior consent of owner due to engine roughness. If the engine would have failed I would not have made it to the next closest public airport. Informed ZZZ Center I had engine roughness and would be landing at ZZZ. I did not declare an emergency since the engine was still running and I had the field in sight with plenty of time and altitude. Made a safe landing with no damage to persons or property; informed ZZZ Center I was safely on the ground; and promptly contacted the owners. They were very nice and understanding and had no problems with the event. At the initial moment I had a reduction in power/engine roughness I believed it to be carb ice and pulled carb heat. The RPM's were fluctuating from about 1600 to 2500; not the typical slight loss of rpm and then rise a few seconds later after pulling carb heat. With fear of possible engine failure I felt it best to make a precautionary landing and have a mechanic check it out in case it was something besides carb ice. I regained power and engine smoothed out after turning downwind to base. The mechanic looked it over and said it was most likely carb ice. I am looking into having either a carb ice detector or carb temp gauge installed to be able to stay farther ahead of potential icing possibilities further in advance in the future.