I have a cub cadet 1550 . have changed plugs ,fuel filter , air filter but idoes not want to stay running. the engine keeps on pulsating. thats with pto engaged or not. no clues.

SOURCE: A short in the pto wiring perhaps?

Form what you are desribing you have a direct short, probaly in the wiring going to pto. I t has rubbed somewhere and is causing your short. Unplug the wires at connector close to your pto clutch and try it again and see if fuse stuill blows after you unhook it.

If the fuse still blows it is in the wiring going back up to thje switch. If the fuse does not blow after unhooking wiring connector the problem is in the clutch.

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SOURCE: Cub cadet Z Force 48 inch zero turn blades won't engage

I hope this will help you...under the side panels on each side of the mower, there are "reverse lockout safety switches", they are supposed to stop the blades when both handles are pulled back. If one or both of the switches are out, the deck will not engage. Also, under the right side panel (when sitting on seat) there should be 3 relay switches, the one closest to the motor controls the PTO., if this is out, the PTO will not engage.

SOURCE: my cub cadet tank stops running 5-20 minuts after

Yes you may need a carb kit. It is not good practice to by-pass the fuel filter. The orifice in the jet is very small.
But anyways, There Could still be a blockage inside the carb, a small leak at the manifold, or the jet is worn out.
Let me know how it goes.

SOURCE: I have a Cub Cadet RZT 50 mower. The left drive

First, check the level of the hydraulic fluid (usually the dipstick is right inside the fill cap, and you just raise the seat to access it). If it's low, fill 'er up with the right fluid.

If that's OK, test if the lack of 'pull' affects the left wheel in both forward and reverse -- try going up a hill forward, and backing up it in reverse. If it affects both directions, maybe you will be lucky -- the problem could be that the bypass for the left hydraulic motor has opened somehow. (The bypass is used to let you push the mower by hand in case of an engine failure, etc.) So look for a fat-headed bolt sticking out of the left hydraulic motor. Check that it's tight -- rotate it just like you would tighten a bolt, clockwise. If it wasn't tight, that may be the problem; just tighten it and try the mower.

If this doesn't resolve it, you probably have a problem in the hydraulic valves, hoses, or motor, and a trip to the dealer is needed. Probably won't be cheap, sorry my friend. Good luck, and please rate if this was helpful, thanks!

SOURCE: cub cadet pto won,t stay engaged

Sounds more like a PTO clutch failure, rather than the switch. The clutch is mounted on the engine shaft, between the hydrostatic drive pulley (nearest the chassis) and the mower deck belt pulley (farther from the chassis).
Since it's an expensive part, make sure the problem isn't in the switch or wiring first. You could do that by probing the wires to the PTO clutch with an automotive test light - they are inexpensive and handy. Clip the ground wire of the test light to the chassis, and probe the hot wire to the clutch (it's the one that doesn't connect to ground) when the engine is running and the PTO switch is engaged. Obviously a helper has to be in the seat, and you should be careful doing this. If the light glows brightly, and the clutch doesn't engage, you definitely have a bad clutch. Good luck! Please rate my answer if helpful, thanks.