Starting

I got a Weedeater One from my wife's boss here's the story she bought it brand new her son assembled it and on the second time using it the left front tire was flat and she didn't realize it well got to close to the curb and it rolled over with her on it. Safe to say the mower quit and she just got some bumps and bruises, I bought it home and checked fuse two relays everything seemed ok I just figured the oil sensor had shut off the motor much less the seat safety. Tried to crank and nothing so read forum and someone mentioned isolate and I thought ok so I tried different grounds and finally got it to start with key on no one in seat or on brakes just pulled starter rope cranks every time???? I also have the problem every time it rains the exhaust muffler fills up with water it blows right out but can't seem to figure out how it's getting in. I agree with a lot of the commenters this is a P.O.S. mower it's hard to steer the belts are so short it's like riding a 200 lb vibrator and no attachments which is probably good the tiny engine couldn't handle it. Told her how far I got with it she said I don't want it back scared the s**t out of her she pays to have her lawn mowed. I know this a reasonably priced mower for what you get but it's not for large, sloped. steep or rough yards.