Rider mower worked OK and then I did end of season service including new spark plug, lube of mower deck, oil change and sharpening blades. It sat idle for some weeks during this and when put back together would run only if choke is semi open. Stalls when set to run position. Have drained tank and put in fresh gas with stabilizer, checked the spark plug gap and lubricated the choke wire houing. Still no improvement... help!!

Was the old gas stabilized? Before and during it was sitting, the gas had fuel stabilizer in it? And it had time to get throughout the carb?

It does sound like either water is in the carb, dirt/trash or gummy gas.

It may be water in the carb or you may need a needle in the carb. The needle, when it gets old, may stick in the choke position. You may be able to fix the problem with just cleaning out the carb.

I had this with an MTD recently, the two bolts for the carb where loose so it was sucking air in at the manifold.

Pete