kmx 125 deristriction & tunning

[KMXKEV]

Probably an old question but any advice would be greatly received, which is the best way to derestrict or tune a kmx 125

[Blink]

Start with a DEP exhaust. Full System.
____________________
The only way to get rid of a temptation is to yield to it.

[Jamie S]

New exhaust, and maybe Re-jet it as well ?

[Finglonga]

Make sure the KIPS is working properly, most bikes its de-activated.
____________________
Andy Sez....
F.Y.Y.F.F.

[lukamon]

hwo do you get the kips working anyway? ive heard something about a softer spring, but where does it go?

and the DEP system, i went to a local offroad specialist and they said dep only make the silencer. not sure if this is true or if they couldnt get it and didnt want me to go elsewhere
____________________
killa wrote: Im an ass man myself

[Blink]

No, they make the full system.

If not, get a full system from somewhere else. The silencer won't make any difference.

google it.
____________________
The only way to get rid of a temptation is to yield to it.

[Blink]

Yep as I thought, get a new front exhaust pipe and change the carb settings.

I researched this thoroughly back when I was 17 and was deciding between a DTR & KMX (google wasn't so clogged with advertising shite back in 2002/3)!

I chose in the DTR in the end! Rode both and both are great 125's.
____________________
The only way to get rid of a temptation is to yield to it.

[bladerunner]

-to deristrict the std front pipe remove it and youll see a restrictor sleeve in the header probably held in place with 3 small welds. If you grind these off and remove the sleeve it will go much better but I'd also check the kips and carb setting as well!

[Blink]

you'll certainly have to tweak your carb (jets).

not really a bit job, scarier than it sounds!
____________________
The only way to get rid of a temptation is to yield to it.

[stevo as b4]

Ok, well DEP do make a decent silencer, and it is worth having, as much for the improved sound and throttle response, more so that bhp. Having said that on the KMX200 the std silencer is quite restrictive.

DEP don't make an expansion chamber for the KMX. There are two choices of performance expansion chamber, in addition to the de-restricted std item. ( restrictor is the same set up as the NSR, in that it's a metal tube with 3 spot welds, situated in the front pipe).

1, Big One (formally Fresco). This pipe is supposed to increase power by around 10% over std, it's louder and much lighter than the std front pipe.

2, Gianelli, The Gianelli expansion chamber is supposed to perform very well, and it seems to add more top end power from 7k upwards, and has a bit more overrev, past 9000rpm, before the power drops off. It sounds really great IMO, and with a DEP silencer, it makes the bike sound far more MX like!

The KIPS valve is not restricted on any KMX after 97, im sure of that! Early ones may have been, but you can check for this by taking off the RHS cover and checking that it has full movement out, which is the high rpm position. When revving the engine in neutral, the KIPS operating arm should swing out fully at or just before 7000rpm. As a further check, you can disconnect the operating arm, and temporay fix the operating rod in the out position. If you test ride the bike now, then you should find that the bottom end power dissapears and that the power comes in quickly at around 7k.

bear in mind that KIPS valves on early bikes were made of alloy. they do seize up in the cylinder over time, and or if the bike is ridden gently everywhere. Then the drum valves, break due to the rack and pinion trying to open them. Broken KIPS valves won't fall into the engine, or damage the piston/bore, but if they seize in the closed position you lose all the top end power.

A std full power/de-restricted KMX should make 20-21bhp at the rear wheel or 24bhp at the crank.

For tuning you can do the following things and more! This is what i would do:
1, Fit a Gianelli or Big one front pipe, and a DEP silencer.
2, Modifiy the std Airbox lid by cutting out the silencer, and opening the entry to the same size as the inner diameter of the filter.
3, Fit V-force reed cage, or Boyesen Rad valve. (same part no. as the KDX200/220 item).
4, Re-jet the std carb to suit the above modifications. If you don't the bike will run lean and is likely to seize! These mods will get you to 23-24bhp r/w.

5, Fit Mikuni TM30 carb. This is a bolt on part and is the best carb upgrade as it fits the std intake and air box connector hoses.
6, Have cylinder head re-profiled and skimmed. The compression ratio is 7.8:1, and this can be increased to 8.2-8.5:1 safely.
7, have the cylinder barrel ported and tuned.

All the above work would see around 27-28bhp r/w or more. Just fitting the TM30 carb should get you to around 25bhp r/w, and is worth doing on it's own.

The other modification to do to de-restricted KMX is change the gearing if you only using it on the road. The std 14/48 gearing tops out at 80-82mph at 10k rpm. You can run 15/48 for about 5mph more top end at the redline, and not lose much acceleration. If you tune it to 26-28bhp then you can fit a 16/48 and run it off the clock (90mph). The KMX speedo is about 5mph overreading at 70mph+.

Lastly you can fit the 200cc version's top end to the 125cc engine. I don't reccomend this as there are alot of small but detail changes between the 200 and 125cc engines. You would certainely need the oil pump, exhaust front pipe, and CDI from the 200cc. The std 200 engine is de-tuned from the 125's spec, so it is torquey and has a very wide power band/midrange. The downside is that it's quite flat at the top end, and a full power or tuned 125 with a decent exhaust and bigger carb feels far more lively, but has alot less torque.

I can't say much about tuning the 200cc yet as i havn't done anything with mine yet, but it's part of the plan for my supermotard.
I've heard that 35bhp is easy to reach however!

[Blink]

Good post steve
____________________
The only way to get rid of a temptation is to yield to it.

[KMXKEV]

Thanx everyone for advice