From: tim@intrepid.gsfc.nasa.gov (Tim Seiss)
Subject: Re: Flywheel weight
Organization: NASA Goddard Space Flight Center - Greenbelt, MD USA
Date: Thu, 21 Jan 1993 14:03:36 GMT

In Message: <1993Jan18.233446.8579@selway.umt.edu>mtrhead@selway.umt.edu (Josh Harmon):

>I ride off-road 90% of the time and need the motor to lug better for 
>more control.  My understanding is that I can get this benefit from
>a heavier flywheel, but what other possible side effects will there 
>be?  
>  .
>  .
>  .
>If anyone has experience with this modification please elaborate, 
>will a permanent weight hurt MX performance? and will a removal weight
>possibly and tragically remove itself?  Does fourteen ounces (Moose's
>usual amount) make that much difference anyway?

Well, as I've emphatically stated several times in the past year in this
group, I am a big proponent of flywheel weights.  I've had one on every
go-fast bike I've ever owned ('76 Penton 250, '88CR250, '89KX250).  Not
only have I always had one, but I've had 3 different kinds:

  1) The Penton had an entire Motoplat ignition/flywheel from a KTM 400
     engine on it, and weighed about 1lb. more than stock.  I traded the
     complete ignition unit from my bike with another guy, so it didn't
     cost anything.  To pay for it would cost several hundred $'s.
 
  2) The CR250 had a Moose weight welded on.

  3) My KX250 has a Steahly bolt-on weight, and yes, it did come off once.
     Only cost me $15 for a new plastic magneto side cover for the engine.

  I rode observed trials from '74 through '77, so my riding style developed
  around torquey, tractable motors.  I raced my '76MontesaCota348 trials bike
  in several muddy Hare Scrambles races in the Spring of '77 and easily beat
  guys on Bultaco 370's, Maico 400's, and Husky 360's riding in the Open B
  class, because my bike was able to hook up and get traction while the other
  guys were spinning wheels.

  ADVANTAGES:
   - Less wheelspin, better traction
   - Less stalling when you let off the gas, more inertia in motor
   - More luggability in tight, gnarly stuff
   - Don't need to slip the clutch as much
   - Pro MXer's even use them on some tracks!(I know RJ used one on some SX's)

  DISADVANTAGES:
   - Motor doesn't rev quite as quickly, but that may be an advantage or
     disadvantage, depending on the situation.  It might slow acceleration,
     but if your rear wheel is spinning instead of hooking up, your not
     accelerating anyway...

   Unless you're a top expert racer on a perfect track, I do not thing a 
   flywheel weight will hurt your MX performance.  I have raced in 6 motos
   in my life (all C class), and have always got off the starting line and
   to the first turn in front of everyone because my rear wheel is hooked up
   and not spinning.  This is just my opinion, however.

   I'm not sure about a 14oz. weight on a CR500, but I had Moose put the
   14oz. CR500 weight on my CR250 instead of the normal 12oz. weight.  Yes,
   it made a difference.  But the difference it made was exactly what I wanted
   and expected for my go-fast bike. YMMV.

   If your apprehensive about the bolt-on VS. weld-on thing, you might check
   out a flywheel weight kit by Klemm Research. In Summer of '89, _DIRT RIDER_
   did an enduroizing article on an '89KX250 and showed the Klemm Research
   kit.  I comes with 3 different weights: 8oz, 15oz, 20oz I think, and are
   fairly easy to change.  They might have one for a CR500...

-Tim Seiss
Xref: sparky rec.motorcycles.dirt:2813 rec.motorcycles.racing:1597