I have never mulched before, but I would think that grass that's a bit tall and wet would cause problems when mulching, so why don't you just pull out the mulch plug and use the bag under those difficult conditions. I just bought a used HR215 MASTERS and mowed grass that was a bit tall and wet with it a few days ago. I pulled out the mulch plug and installed the bag, and the mower produced the neatest cut I've ever seen with no signs of the engine bogging down. I even tried out the 3rd gear for a while, but I had to run to keep up with the mower, so I lowered it down to 2nd gear, but the mower cut great in all 3 gears. I suggest you install a new spark plug (of the type and mfr specified in the owners manual) to be sure an old or wrong type spark plug isn't causing an engine performance problem. 2-yrs ago I installed a new spark plug which I bought from ACE Hardare (their brand) in my Honda snowblower. 2-weeks later I obtained the correct spark plug and installed it, and the snowblower seemed to be running faster, so I got out my tach and checked the engine rpm with each spark plug, and I found that the correct plug gave 200 more rpm than the ACE plug.