I submitted a reply yesterday and this slow site did not let me post my reply.
One more time. Site is erratic speed, etc.
Does the engine run at WOT or are you just seeing WOT with the engine not running?
WOT with the engine not running can be a normal thing is why I ask.
Here is a link that...
You need to read the pto clutch amps. Do you have a ammeter?
or install a 10 amp fuse or ckt breaker in the electric clutch ckt.
You can get automotive type ckt breakers from Amazon in a kit of several sizes very reasonable.
On your idlers make sure that they are the correct OD.
It's quite common now days to order the correct v belts by part number but the size you receive is not per specs for the tractor.
I use a upholstery tape measure, cloth type tape 1 inch wide and about 12 ft long from wal mart sewing...
I would use a electrical tester and do some logical testing. (instead of farting around)
You can get one at wally world and read the instruction manual about how to use.
Look at page 30 of the owners manual.
It appears that maybe on that machine:
When you are not on the forward or reverse pedal the belt going toward the engine pulley should be loose/slack enough that it slips on the engine pulley for neutral. Also make sure it's routed correctly per the diagram...
How was the drive motion acting before you changed the drive belts.
I seen a owners manual/parts list download at the sears link.
https://www.searspartsdirect.com/manual/5efdw0nkch-000736/mtd-13ag601h729-front-engine-lawn-tractor-parts
Keep a heads up when working on the brake if replacing the...