I just want to point out a few things I feel are worth noting. First to the OP. Please learn proper lawn equipment maintenance. Leaving today's gas in a mower over the off season is silly, even if your using a stabilizer. The ethanol in most fuel will pretty much turn to water (in lay terms) and render your practically new mower useless. Just Google ethanol gas in lawn equipment and read up. Then Google "lawn equipment maintenance" and do the same. Its for your/your wallets own good. Second to saxman, Honda mowers dont suffer from sticky valves that often. Especially after this short of a time. I fixed a guy who acquired his father in laws HRX that sat for 1.5y with fuel in it and even though his carb had pretty much straight water in it and was rusted on the inside (blew my mind) the valve was not compromised in any way.Personally I have never even ran across this issue. Not that it doesnt happen but I just feel its pretty uncommon.

IMHO changing the oil on an hour basis regardless of how it "looks" is important. The OEM does not come up with these hourly change numbers by using a dartboard. Keep in mind with 20/20 vision you cannot see particles less than 40um (contrasting no less) without magnification. Even on units with an oil filter, they are rated at 20 or 25um and particles less than that size cruise through the filter unless they get hung up as the filter clogs. Worse, oddly shaped particles say 15um wide, and 35um long (like a spear) can pass through a 25-20um filter. Changing the oil (when warm after the particles have been stirred up into suspension) is the only way to rid the engine of them other than flushing the case. These small particles crash into parts and make more small particles, or some larger ones too, and the cycle only ends the day the engine stops running for good. Keeping the oil changed at the recommended interval rids the case of the majority of the particle population so you have fewer projectiles in there with fresh oil. In hydraulic systems we deal with this another way as it would be impractical to drain a 1,500 gallon industrial reservoir on a regular basis. The use of 10um, 5um, or 2um filters (incidentally a 10um filter would remove all the red blood cells in your blood, and a 5um would strip the white cells out leaving you only with plasma, so these are FINE filters and not the one on a Briggs engine.) and occasional external purification by use of a purifier unit keeps the oil dry (water removal) and clean. Since it would be impractical for the average homeowner to own an oil purification unit (the good ones start at $22k) and reprocess the used oil with new additives, changing it regularly is the best line of defense. After a season (25 hours) I am sure there is more than 300ppm of water in the oil, not to mention gas too.

My guess is that the carburetor needs serviced or replaced.

You have something binding. When you remove the long studs you need to use longer studs to put back on. I am sure you have something binding. You should be able to freely move the gas throttle by moving the lever from the governor. Look at the parts sheet on any good Honda parts site to see what you may need to adjust.