My RZ4623 will not move.

Question edited for clarity.
Question moved from Cars and Trucks category.

If it runs backwards, then the problem but be the forwarding part of the controller. Usually your local Model Shop will know a repairer, or they might undertake it themselves.

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Question edited for clarity, full 'make model (what it is)'.
Question moved from Cars and Trucks.

Some ideas here

https://www.google.com/search?q=Husqvarna+rz46i+drive+slipping

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Check out the help in the link.

https://www.google.com/search?q=Vermeer+SC252+stump+grinder+moves+slow+forward+and+backwards

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Check the leftside manual transport bypass lever has not somehow engaged. Compare it to the right side.

The two transaxles are driven by the same belt so extremely unlikely it's a belt problem.

Look for any signs of fluid leaking from the left transaxle shaft seal. If the seal has been leaking then it may be low on fluid. The transaxles are considered maintenance free so there are no instructions from Husqvarna for adding fluid but it can be done. However, if the shaft seal is leaking it will need replaced.

See operators manual regarding bypass levers (rods).

https://www.manualslib.com/manual/74128/Husqvarna-115-127127-Ir.html

Check transaxle bypass is closed (rod is all the way forward).

I have seen a number of domestic rotavators but haven't yet seen one with a reverse gear. You didn't make it clear in your description whether yours has a reverse gear and that is all that is working or whether it usually only moves forward but is moving backwards?

While it is theoretically possible for a 2-stroke engine to run backwards, your engine is a 4-stroke that is incapable of running backwards and so it would seem the gear selector is stuck if it has one or someone has carried out repair work and made a mistake or something else is broken.

The only thing that comes to mind is some of the older designs used an over-long drive belt that crossed in the middle like a figure eight in order to reverse the driven pulley and replaced the belt with one that seemed the right size would cause the machine to run backwards.

More information needed, perhaps...

There is a switch under you seat or attached to your seat somewhere that is probably not activating or is bad. This switch has to be fully depressed to activate the drive. It is a safety feature.

Could have broken the shear pin in the drive pulley. If one of the pulleys turns when you put it in gear but the other pulley does not turn then the shear pin is broken or missing.

Probably. There may be a solenoid not working which is keeping the transmission from engaging the forward gear train but for it not to work at all is unusual.

Are you sure its not just your belt on the beater of head slipping and needs to be replaced?