On Tue, 5 May 2015 19:56:10 +0000 (UTC)
HerHusband wrote:

I have had a lot of issues with that. I could get the blade to track
in the center of the top wheel, but it was almost ready to fall off
the bottom wheel. I've shimmed the lower wheel a couple of times but
was afraid to shim it out too far. I installed the polyurethane tires
and added one more shim yesterday and finally got it to track in the
center of both wheels. I'm not crazy about having the lower wheel
shimmed out 3/8", but it seems to work OK.

i would look more closely at the bottom wheel and drive train
something sounds wrong there