My mower will run fine while the blades are engaged, but when the bail is released and the blades stop, the engine will sit there and surge. I have used fresh gas and used a little seafoam, but since the engine runs fine when the blade is engaged, it just seems to me that this is not a fuel issue. Also this only does it when the engine is warm. For example, when the engine is first started, it runs fine. Once I mow a little bit and stop to empty the first bag, it will surge.