I'm very surprised that you are able to run well below 540 rpm without clogging the unit. Whenever I have put branches in mine without spinning it up correctly the chute clogs. Maybe you don't run pine or anything sticky.
I'm also amazed you aren't slipping belts - my tractor will easily slip the belts before stalling the machine, and I'm running half the horsepower you have. One of these days I'm converting mine to chain drive.
I run them fiddle string tight and keep the pillow blocks greased with high quality teflon fortified grease, same stuff I usr on my farm implements. I've never slipped a belt, the Weasler will slip before a belt. I'd avoid a chain drive because of the inherent chain slo / slap as it drives the shaft, especially with no slip clutch on the output, thats asking for a disaster. The cutting action isn't continuous, it's an impact cut and that will cause chain slap / slop. Thats why the belts are better able to rake the shock load.
I run pine all the time, no issue. I did have issues before I drilled 10 1/2" holes in the knife access cover on the backside of the machine. No issues after that. Even at half throttle there is a very noticible output of air from the discharge chute. I keep my knives sharp too. I own a machine shop and I purchased an angle jig for one of the big surface grinders. I jig a blade on the grinder and sharpen it, takes about 3 minutes a blade. The I take a fine oilstone and stone off the wire edge and the knife is razor sharp. I also bevelled the anvil on the entry side to allow a smoother feed of material. The anvil sits a bit proud of the
chipper base, now there is a sloped entry, makes for a better input flow.
Far as I can ascertain, blade sharpness contributes as much to output flow as does the extra air intake on the backside. I realize most owners cannot sharpen their own knives and hand sharpening won't work because you cannot maintain the constant angle (27 degrees) that is necessary for proper chipping. No problem here, in fact I was thinking about running an ad on Flea Bay for grinding knives.
It don't matter what unit you have, Woodmax or Wallenstein or Jinma, dull blades equal a poor chipping situation and possible chute plugging. All the manufacturers sell replacement blades and anvils but in reality it's much cheaper to resharpen and the blades and anvils are through hardened and stress relieved so in theory, you can sharpen a set of knives many. many tiimes before replacement.
I tend to changeput mme every spring. I keep 2 complete sets, one in the machine and one on the shelf, ground and ready to go in. I just grind the anvil face perpendicular to the flywheel and take off any nicks. There is a lot of adjustment on the anvil on relationship to the knife clearance.
On clearance, I use an old credit card to space the knife to anvil clearance. That seems to work the best. About 0.030.
