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Help! Kx 125


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#1 rathairthir

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Posted 17 December 2014 - 09:33 pm

Hi folks.  

Yes I know its a TDM forum but I need some help.  :help: So I reckon the is the best place to go.  

 

My 14 year old son has been pestering me for a " Field " bike for Crimbo so I found a KX125 that needed work. The last few weeks have been spent hiding in a neighbors shed fetteling away. Fork seals, carb clean, discs, pads, calipers, clutch basket(bodge) oil seals, etc, etc.

 

The problem is:  

I finally got it running right and found a quiet spot that I could "pootle" :oldgit: about on it before the 25 th.   :istupid:

Sweet holy baby Jesus .. It unleashes a new demon from hell with every gear change  !!!!   Its either spinning the back wheel, popping the front, or both at the same time... While this has brought a bit of life back into this old dog, I cant give it to my son with out some sort of exorcism.  My wife is quite fond of the boy so I have to tame the beast... This is where your collective knowledge comes in.. I hope...

 

I have drilled and threaded the twist grip and fitted a screw to restrict throttle movement and am considering the twist grips with reduced travel but I am wondering if I there is any other way of making it safer.

 

Can I disconnect the power valve and lock it closed WITHOUT CAUSING HARM TO THE ENGINE. Coking etc.

Can a restrictor disc be fitted to the carb to slow it.  If so,  size, linky etc etc 

 

He has never ridden a twist grip with clutch lever before so you can imagine how stupid I feel with a week to go and a mass murderer parked in the shed..

 

All / any help greatly appreciated.  Abuse also accepted.

 

Time is ticking and  insanitycaluse is on the way

 

HELLLLLLP!!!

 

 

 



#2 jono49

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Posted 17 December 2014 - 10:06 pm

In the history of Irish road racing there was an era when TZ Yamaha's filled the entire field of most road meets, and very well fettled a lot of them were too, so I'll be very suprised if your not living less than a mile away from someone who has all the answers you need regarding the two stroke side of things?

I know they will have tried to enhance the performance of the machines they worked on, and your wanting to do the opposite!....but I'm sure they'll know how to do that as well :lol:


Edited by jono49, 17 December 2014 - 10:10 pm.

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#3 muddy

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Posted 17 December 2014 - 10:28 pm

Blow that, sounds like you need to keep it for yourself and get him a C90.


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#4 leehenty

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Posted 17 December 2014 - 11:40 pm

Depending on how the carb works, put a small brass tube over the cable to the slide inside the carb to restrict how far up the slide can go. 

You may need to experiment and find a way of sealing the carb top shut to stop little johnny taking it out and unleashing the beast within.

My nephew has a kx125 and I think the carb is a 36mm round slide type with top cable entry. IIRC


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#5 Studley Ramrod

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Posted 18 December 2014 - 07:44 am

Couldn't you make the gearing taller ? :unsure2:  Or get him to eat more cake ? :cake eating:


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#6 Favs

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Posted 18 December 2014 - 07:54 am

Wot Lee sed  :good:


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#7 rathairthir

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Posted 18 December 2014 - 11:04 am

Thanks for the input gents.

 

I did find a few locals but their only goal ever was to make it angrier and couldn't understand why I would want to tame it. 

 

The carb is a top entry and I contemplated fitting a section of 1 1/2" waste pipe on top of the slide to restrict travel but unfortunately it is not round, its more of a cresent moon thingy ( never saw one before) so that was out.  I did fit a plastic tube to the cable above the slide but it was difficult to get the right length and it jammed once so thats where I left that !!  Jamming open is  definately out.. I should have mentioned this in my first post.  Apologies

 

Trying to trade it in a week could also be a tall order but.......

 

As for gearing I reckon it'll only give the bassid longer legs to run with..

 

Still thinkin about locking the power valve but dont want to do harm either. :hide:

 

As for cake !!! He could eat it all day long and still be hungry.. Tape worm I reckon  :)



#8 leehenty

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Posted 18 December 2014 - 01:52 pm

Power valve locking might be more complex unless you remove the push rod, as it's a mechanical link which raises the effective edge of the port at higher revs which has the effect of altering the port timing. At low revs the port is lower so you get more torque as the piston traps the high pressure gasses for longer. High revs you need the get the burnt gas out as fast as possible.

Limiting carb opening would be the most effective method I feel.


Edited by leehenty, 18 December 2014 - 01:56 pm.

2002 900 silver,oil pressure switch with brass 90 degree conversion, RG fork protectors. Wilburs custom made rear Shock with remote hydraulic preload and RG shocktube, Wilburs front springs. Scotoiler with a custom made swing arm delivery unit. Silicone radiator hoses.BMW 1150 handguards with Touratech extensions, Carbon Fibre yoke cover and fender extenda, MRA flip screen, Yamaha Engine bars, SW Motech Centre Stand, Kappa wingrack three box Luggage with E21's as option from the K960 boxes, Zumo 660 satnav on Touratech mount, Led Voltage monitor, Baglux tank cover, Clear LED Rear light, Aux LED brake light, BikeVis bullet LED's under front  nose,Stainless rear axle nut, stainless chain adjusters, stainless wheel spacers front and rear, Probolt Polished Stainless Flanged Hex engine screws, Polished stainless fairing screws, stainless disc bolts. Titanium brake pins front, Probolt Titanium Flanged Hex Front Caliper Bolts & Rear caliper slide pins Adventure Spec Tool tube under rear rack, left and right sides with custom alloy mounts.<p>Top Sellerie double gel pad seat. Carbon Fibre inner dash and side infill panels. Anodised black alloy swingarm pivot bolt covers and footpegs, Nano II Gear indicator.

#9 Rallyist

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Posted 18 December 2014 - 03:30 pm

Weld a washer in the exhaust to reduce the diameter by half, that will slow it down.


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#10 divvxj

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Posted 18 December 2014 - 06:03 pm

Weld a washer in the exhaust to reduce the diameter by half, that will slow it down.

:good:



#11 Catteeclan

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Posted 18 December 2014 - 07:05 pm

Weld a washer in the exhaust to reduce the diameter by half, that will slow it down.

That's how most of the mopeds are restricted now days.


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#12 rathairthir

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Posted 18 December 2014 - 07:45 pm

Gzaust off tomorro so.  Its held on with springs and a very light material so there may be more "jamming" than welding.  I think its bout 1 1/2 " diameter so i'll have to open the "Big" washer box..   Problem is the little barsteward is off school so its cloak and dagger time again..

 

Thanks for the help and keep the ideas coming !!



#13 rathairthir

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Posted 19 December 2014 - 08:31 pm

Right !

 

I did a bit of rummaging last night in my sh1t drawer and found the restrictor discs off my 850, thanks Alex, :good: ( I needed them for the test ), and after detaching my limpet child :whatcha:  I got 15 mins to check it out.  Disc  OD  is 45 mm and ID is 20 mm.  This turns out to be about the same size as the exhaust flange... Soo. the disc is now fitted between the exhaust flange and head and held in place by the two springs.  It is effectively reducing the diam from 42 to 20 mm.  I did manage to start it and give it a quick revvvv and it now sounds more Monsters Inc than Beelzebub but I still haven't had a chance to let it warm up, not to mind run it..

 

Not bad for 15 mins in a dark shed with a head torch and a suspicious child prowling around outside..

 

Again I put it out to the collective..... What are the chances of doing major harm ie big ends, mains etc.  stuff that will cost lots and require splitting the crank case..

 

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#14 harvey krumpet

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Posted 19 December 2014 - 09:20 pm

I was going to mention an exhaust washer. That's how the KMX's were restricted.

 

My old KDX 250 behaved the same way in top gear.... K'in scary.

 

Taking the back mud guard off will help, too. Trust me.


Edited by harvey krumpet, 19 December 2014 - 09:20 pm.

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#15 Rallyist

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Posted 20 December 2014 - 09:13 am

 

Right !

 

Again I put it out to the collective..... What are the chances of doing major harm ie big ends, mains etc.  stuff that will cost lots and require splitting the crank case..

 

:signthankspin:  

 

 

Won't do any harm to the motor as no mods have been done to effect mixture control so oiling will be the same you have just restricted gas flow through the motor. :good:


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#16 Catteeclan

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Posted 20 December 2014 - 10:08 am

Are the springs strong enough is the question.


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#17 leehenty

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Posted 20 December 2014 - 01:18 pm

So long as little johnny doesn't figure out why its going a bit slower than he would like, it should be ok.

He will be fine, at 14 any bike is a big step up in status, so he will be busy enough staying on it rather than thinking about going faster.

When he's learned the basics, take out the washer to give him the pep when you feel he can handle it.

Involve the lad in the spannering after he gets it, so he learns to fix it himself. It will stand him in good stead for when he moves up to a TDM in about ten years time.


2002 900 silver,oil pressure switch with brass 90 degree conversion, RG fork protectors. Wilburs custom made rear Shock with remote hydraulic preload and RG shocktube, Wilburs front springs. Scotoiler with a custom made swing arm delivery unit. Silicone radiator hoses.BMW 1150 handguards with Touratech extensions, Carbon Fibre yoke cover and fender extenda, MRA flip screen, Yamaha Engine bars, SW Motech Centre Stand, Kappa wingrack three box Luggage with E21's as option from the K960 boxes, Zumo 660 satnav on Touratech mount, Led Voltage monitor, Baglux tank cover, Clear LED Rear light, Aux LED brake light, BikeVis bullet LED's under front  nose,Stainless rear axle nut, stainless chain adjusters, stainless wheel spacers front and rear, Probolt Polished Stainless Flanged Hex engine screws, Polished stainless fairing screws, stainless disc bolts. Titanium brake pins front, Probolt Titanium Flanged Hex Front Caliper Bolts & Rear caliper slide pins Adventure Spec Tool tube under rear rack, left and right sides with custom alloy mounts.<p>Top Sellerie double gel pad seat. Carbon Fibre inner dash and side infill panels. Anodised black alloy swingarm pivot bolt covers and footpegs, Nano II Gear indicator.

#18 rathairthir

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Posted 20 December 2014 - 05:02 pm

Thanks Gents.  The limpet was firmly attached today so no hope of getting a look at it and may not again until the un-veil..

 

The Exhaust is held on by springs so its only an extra 1mm extension on them so should be OK.

 

I do plan on de-restricting it soon enough but I want to get over the usual learner cock ups first.  Panicking and pulling the front brake and throttle at the same time. Pulling the clutch, not throttling off and dumping the clutch in a panic. High side. Low side .. Etc Etc. I plan setting up a few cones in the field and give him a bit of a gymkhana to play with. 

He is smart enough to know that if I have restricted it, it's for a good reason.  Trying to drum into him that its not a toy that all his buddies can "play" on is going to be the hardest part. Thanks again.  

 

Will update when I get it out for a rip..



#19 rathairthir

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Posted 25 December 2014 - 01:41 pm

Happy christmas all. Quick update. Runs perfectly and well restricted. Just enough power to get it goin but not enough to flip it or slide it. I hope. He is pretty ok too but plenty of room for improvement. Thanks again all. Enjoy the day.

#20 jono49

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Posted 25 December 2014 - 07:43 pm

:good: Glad it all worked out for you!


Don't get confused between my personality
and my attitude. My personality is who I am,
my attitude depends on who YOU are!

 

Skinny people are easy to kidnap.....Stay safe and eat cake!!!!!



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