[Farmall] 340U brakes fixed - now questions about PTO

[br549 at hemc.net]

I got new parts from Hoober and eBay to get the brakes into working 
order (the RH side pad material had separated from the metal backing 
plates!). I needed to do some bush hogging and got to use the PTO 
for the first time. What I found is when I get into thicker grass, the 
blade / PTO will "choke" and stop turning. This does not change the 
RPM of the engine. It seems that if I pull up on the PTO engagement 
handle, the PTO immediately turns at the correct speed.

If I understand correctly, the PTO should be fully engaged by just 
releasing the handle from the off / lock position (is there a locked on 
position too?). Is the linkage for the engagement handle out of 
adjustment? What other things could cause the PTO to slow / stop 
under such a light load? How can I tell what type of PTO I have (clutch 
or gear)?