I have a L185F which is similar in the family of your L235.
On the tachometer you should have a mark that shows where the engine RPMs needs to be to get 540 RPM out of the PTO (assuming that you have the PTO in the correct gear)
My PTO has 3 speeds 540, 700 and 1000. First PTO gear on mine is the 540 PTO speed.
Here is a link to another discussion on PTO and engine speeds where I quoted information out of the operation manual.