Befco RFM Help Please

[Merlin1]

We have a 72" Befco rear discharge mower behind a Kubota B-7800. It was bought in Jan of this year and has only been used 8-10 times this year with the drought. I recently put some high lift blades on it and since then it has thrown the belt twice. It seems to happen every third mowing or so and I can't seem to put a finger on what's going on. All the pulleys run smooth with no apparent wobble and no obvious misalignment. There is no vibration that I can feel that is different from the first use.
Any thoughts guy's.

 

[RoyJackson]

It sure sounds like your belt tensioner is not doing the job.
On my 60" Befco, there are two positions for the tensioner.

I can't say with certainty that's your problem, but check your manual for the belt tensioner information.