Balance it!!  But also balance the rods, and ideally, you should have a
counter balanced crank (although that's pricey and extreme).  The better
the balance in the engine, the smoother and more efficiently it will run.
Also, the longer it will last.

I'm a big believer in balacing and blue printing engines.  These are small
engines that need all the help they can get, and everything that is
unbalanced steals power.

However, I would not do it the way Muir suggests (I tried it once the
results were too inconsistant).  I would take it to some shop with
experience and the proper equipment (a very accurate scale) to do a good
balance job and go for better than .25 g .

James

Red '93 SLC
Red '87 GTI
   and
'67 deluxe
'71,81,'85 Westies