Small Engines (Lawn Mowers, etc.): Engine idles Rough, twin cylinder engine, mtd lawn tractor

Question
I have an MTD lawn tractor 18.5 hp model 690 series. Just recently the engine doesn't idle properly. The idle goes up and down after being started. I have changed the plugs and fuel filter. This is a briggs & stratton twin cylinder engine. If I pull out the choke a little it runs better. Is this a carburetor problem?

Answer
Very common symptom for a dirty carb.  I would recommend removing, dis-assembling and cleaning the carb with compressed air from an air compressor and carburetor cleaner.

Those carbs are pretty straight forward.  Just pay attention, take some digital pictures, of how the carburetor linkages are connected.

There may be a fuel pump on the front of the carb.  There are two small springs inside...be very carefuel and pay attention when you dis-assemble it.

Let me know if this helps.
Eric