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Posted by DanKMTB@gmail.com on August 4, 2008, 10:26 am
> *********************************************
>
> >On Sun, 3 Aug 2008 10:51:40 -0700 (PDT), "DanKMTB@.com> wrote:
> >Hi,
>
> >I have a 2002 KX125 that I am looking to rebuild the top end on.
> >Which piston would give me the best low & mid range torque
> >improvement? I'm not too concerned about top-end, but would like a
> >little more low and mid. What piston would you suggest and why?
> >Would a high-compression piston increase low and mid, or is that more
> >of a top-end improvement?
>
> >Thanks,
> >Dan
>
> *************************************
>
> Dan,
> Higher compression will give you more low end torque, and won't hurt
> top end a bit. No matter what compression the piston gives you to
> start, as soon as the rings start going away, you will lose it. Pay
> attention after the rebuild and replace the rings as soon as you can
> tell (by feel) or measure any difference in compression.
Thanks. I couldn=92t remember what part of the power range high-
compression helped, so this is key info. Appreciate it.
> The piston isn't going to make a lot of difference in power. You
> might bump up the compression a bit with a special piston, but (as far
> as I know) you are always going to be stuck with a single ring piston.
>
> Your piston selection should probably be made in consideration of
> lightness, strength, and wear, as well as frequent ring replacement
> costs. (If you are really serious about keeping the most power, you
> will want to replace the piston ring fairly frequently.)
I am willing to replace rings and anything else as necessary =96 I enjoy
a good excuse to play with my tools. The previous owner seriously
neglected maintenance, and I plan to turn that around 100%.
> You will best tailor your power by:
> (internally) possibly reshaping the head and keeping the bore good
> and tight, reconditioning as soon as it is no longer round.
Again, I=92ll do what is necessarty, but I=92m on a budget and am a lot
more eager to twist some wrenches myself than I am to get into work
like this. If need be I will, but that=92s a big hit to the bank, and
I=92m trying to keep the tab within reason.
> (externally) PROPER JETTING.
This is somewhere I=92m going to need to do some learning. I figure I
could pay to have it jetted for what I=92ll spend learning, but the
knowledge will pay off in the long run. Any suggestions for resources
when it comes to learning jetting?
> Also, with different reeds, pipes,
> silencers, and possibly re-timing the powervalve, one can enhance
> different areas of the power delivery; but it's almost always at the
> expense of another area of the power delivery. But proper jetting and
> the right pipe will give you the most of what you are looking for.
Again, I need to learn here. The bike already has aftermarket reeds
(as well as almost everything else) but I=92m not sure what model, and
what type of performance they were after at the time of the mods. I
assume top end, based on the fact that the bike was raced and the way
it performs now (all top-end, almost nothing else).
> I was always a fan of Pro Circuit two stroke pipes, since they
> seemed to give a little more power everywhere over stock (with proper
> jetting).
> FMF pipes seem to be tuned to enhance more specific areas of the
> power delivery. (Gnarly, Fatty, or Rev model pipes. Although the SST
> was/is supposed to simply work better everywhere, I wouldn't really
> know.)
The current setup is an FMF platinum pipe with an FMF q series
silencer. It had a Pro-Circuit 304 shorty silencer, but that was too
loud for where I ride so I went with the Q. I noticed a bit of mid &
low-end power improvement upon replacement of the pipe, but not as
much as I am looking for.
> The main thing is to be properly jetted (with a freshly packed
> silencer and good reeds), piped, and geared for your purposes.
I=92ve got a new silencer, so the work to be done is jetting and reeds.
I already asked for references on jetting, so how do I tell if the
reeds are =93good=94? They are aftermarket quality reeds (boyseen I
think, I=92m not near the bike at the moment) but I don=92t know how to
tell if they=92re worn.
> Good Riding!
>
> Jim
Thanks for all the input! I really appreciate the help.
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