Worm gear has a hard spot, and doesn't turn freely. Tines will run for a short period of time and then stop.

The following was extracted from the Mantis owners manual..

At some point, you may find that the tines won't turn when you press the throttle. This may mean the engine isn't sitting all the way down on the worm gear housing. Perhaps you've been using your Tiller
for several years. Or perhaps you've removed the engine for use with the Mantis hedge trimmer attachment, then replaced it. In either case, the flange bolt may have come loose and lifted the engine up.
If this happened you'll notice a gap between the bottom of the engine clutch case and the top of the worm gear housing.

To fix this, loosen the flange bolt. Take the engine off the worm gear housing. Notice the hex head on top of the drive shaft . Inside the clutch case, you'll find the clutch drum. Make sure the hex head
lines up with the clutch drum inside the clutch case. Then put the engine back on the worm gear housing. Make sure the plastic carrying handle is not under the fuel tank. If you've followed these steps properly, there will be no gap between the clutch case and the worm gear housing. Make sure you tighten the flange bolt.

The best way is to disassemble and inspect because there is no need to buy parts you won't use. Most likely be clutch or the worm gear. Some of the worm gears can be removed from the shaft and some are made onto the shaft. Hope this will help

Hello, Did you notice if the tines moved when you turned the belt pulley to install the new belt? If the tines do not move when you rotate the driven pulley by hand, the worm gear might be stripped. If the tines do move when you rotate the driven pulley by hand, the belt tensioner might not be working properly. It could be as simple as an adjustment.

Is the motor running and increasing power with movement of the throttle lever? If so then something is possibly caught in the worm gear mechanism.

PPB2000 more than likely has stripped a gear in the gearbox. The drive cable is probably ok. Tines are driven by a worm gear and brass gear. Internal parts of gear box not available.
jas

if you remove the shield the worm gear clamp goes through a hanger the hanger is spot welded to shield I have found them unatached ,,another wa y.. remove 1 shield at time see if rattle stops ';';;' rattles are hard to find sometimes ';';';

Don't worry about the Worm Gear for now. You have to make sure that the Motor
is fully functional by itself: Remove the Transmission Housing Cover (4 screws) and
the two screws holding the Motor down. Lift the Motor off the Worm Gear and set it
on the side (be careful of AC voltages from the Motor and Control Assembly).
Select Stir setting and observe the motor shaft. Is the Motor running? If it is,
Select other speeds to see how the motor performs.
With the motor now fully functional, you can now check the Worm Gear Follower
for worn out/broken teeth. Remember the motor drives the Worm Gear, it then in
turn drives the Worm Gear Follower (you may have to remove the grease to see it)
The Bevel Gear sits right on top of the Follower and drives the Attachment Gear.

http://www.mowerpro.co.uk/page/lawn-mower-parts/

Well hopefully it's not the transmission, as sometimes these tend to go. Another common but cheaper repair are the two bearings where the tines connect to the unit.

MORE THAN LIKELY.. The bearing is located above the worm gear housing, the part connected to the tines beneath the guard. This removal can be somewhat frustrating but if you remove it and remove the engine flange you'll be able to manually spin the drive shaft and see if it's the worm gear housing/lower bearings or if it's the more likely bearing on the clutch drum or the clutch itself.

Your worm shaft or tine shaft and gear assembly are probably shot. Welcome to the club. Long live American manufacturing.