I thought that also but did'nt take the time to try it like a dumbazz. The cars always revved higher when they had a gasket leak under the carb and I would spray the cleaner.
I vote the seals too.Similar issues had with the 4200.Cold it was working perfect.After a couple of cuts it didn't falling to idle imidiately after WOT and revving on one side.The clutch side seal had punctured the lip(someone attempted to replace the seal but with not much luck).