2stroke

Member
Nov 7, 2001
399
2
I race a '75 KX400 in stock form, it has a light switch hit and is tempered for all the world just like a 125. Its only happy when the Rs are on, and then look out, its ALOT to handle. I can be a total hooligan on the straights, but everywhere else is a bit tough. I want to make it more manageable. I thought about a flywheel weight. Steahly lists one for a 93 KX250...( I owned one once)...it threads on using the left hand threads used by the magneto puller. Now, I know, having had both bikes, that the puller is the same for my KX400 as it was for the 93 KX250....and most all the other Kaws for that matter.....

Is the flywheel weight a simple hunk if metal or do they have a custom weight distribution for a certain motor? If they were unequal in some way to match a specific crank, I would imagine they would ahve to be indexed in some way and I cant see from pictures that they are.....
In other words, Im sure the 93 KX250 weight will bolt up, but will it shake my mains apart?

I also thought about adding a head gasket or two to lower the compression.....
 

helio lucas

~SPONSOR~
Jun 20, 2007
1,020
0
the fly wheel weight doesn´t do anything to improve motor balancing, that should be done by manufacturer on the crank, assuming they get it right ;)
you have to be carefull to get that FWW because between the fly wheel and the cover may not have enough space available.

the lower compression thing works great for a cheap mod but porting is the real trick to make those bike smooth. the goal is to change the engine characteristics.

a set of boyesen reeds usually do much to improve power delivery and smoothness. :cool:
 

jason33

Member
Oct 21, 2006
655
0
fly weight smooth out the hit, but prolly wont fit under the side cover unless designed for that bike,and yea there are a few different weights to choose from on certain bikes
try boost ports, new reeds,and maybe adjust the timing
quick low end cheap power - use a small front sprocket,the smallest one available,then jet it ,use good premix oil i use klotz 40:1 in my old kx420 it works well,also a good silencer and pipe will make a big difference,if dg or pc,fmf make them but there pricy
 

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