Starter staying juiced! Please help!

I need some serious help my friends. Im working now 5 days on a customers troy bilt pony 2009 model. I replaced a pulley and after hooking up the battery the solenoid started clicking when i would crank it. So after i started going through my methods of checking whether the starter was getting juice because it wouldn't do anything. Suddenly while checking a poof of smoke came out from under the shroud. I found the magneto burned. So i replaced it and the solenoid. Checked the starter it works. So i began putting everything back together and now when i try to put the negative cable on it sparks a little and engages the starter. It doesn't turn the motor over but it engages the pinion gear. New solenoid checked its good. I checked my cable to the starter and im getting 12v when i got from cable to ground with my meter. Im also getting 12v on the green on my solenoid. Its a 4 post solenoid. I dont know what else to do. I cant find any burn marks on the wires. I cant check the alternator because i dont have the bolt long enough for my puller. Please help.

Check the key switch. Sounds like a similar problem I had. The switch contacts built up corrosion and moister jumped the current.

The magneto burns because power is getting fed down the kill wire.
So either you have swapped the fuel solenoid wire & the magneto wires over or you have problems with the ignition switch.
The control wire on the solenoid should be open and only go 12V when the ignition is in the start position.
Depending upon how the mower is wired , on some you can cross over the start cut out and the engine kill wires on the PTO switch or the brake switch.

RE-check your starter solenoid P/N's ....... you stated you changed the solenoid among other items.
Long ago I saw the situation where the solenoid was replaced and the starter instantly engaged , seems the solenoid was "triggered" by providing a path to ground for the center or 3rd terminal .... somehow it grounded through the ign. switch... Sorry I cant remember much other than once the correct solenoid was installed the problem cleared . ....... Boobala