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Good Morning!
Last week was the first mow of the season and it ran great for two hours. This week, when I engage the blades, after about a minute or two, I'm getting a weird surging issue when moving. The blades sound like they're engaged fine and then for a moment, it'll sound higher, like the load has been taken off the engine, as if the blades aren't engaged. It'll go back and forth like that until I stop moving. There was also a burning type smell present. Once, when I tried to restart it right after it happened, it didn't seem like the engine wanted to turn over. I let it sit for ten minutes, tried again and it started fine but once I start moving again, the same thing happens. Some additional info, if it matters, I just changed the fuel filter and did an oil change last week, the oil level is fine. The belts look good but there's 250 hrs. on this mower and I've done nothing with the plugs since we purchased it new from the dealer, three years ago. The maintenance schedule says to check condition and gap every 100 hours. I'm picking them up today, I'm assuming I should replace them by this time. One last thing that I don't know if it has any bearing or not, the Revtek system worked great the first year. Last year, the light showing that it was engaged would start turning off by itself when I rode over a bump and I'd have to push the button again for it to light up so I could mow in reverse. It's continued to keep turning off over bumps this year. I just wasn't sure if it's integrated with any other system that might be causing the issues I'm experiencing. Any ideas at all would be greatly appreciated.

You need to check air gap at PTO Clutch, remove deck for access.