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HELP MEEEE!!!! RD125 LC 1984 (A)

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majortom86
Two Stroke Sniffer



Joined: 20 Jan 2011
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PostPosted: 14:02 - 20 Jan 2011    Post subject: HELP MEEEE!!!! RD125 LC 1984 (A) Reply with quote
HEY U GUYS I HAVE A BEAUTIFULL RD125LC MRK1 ITS FAST BUT NOT AS FAST AS IT SHOULD BE AND WEN IN 3RD GEAR IT SPLUTTERS A BIT AT 6GRAND MOST PEOPLE SAY IT SHOULD COME UP ON BK WHEEL IN 2ND?? BUT SADLY IT DOESNT ANY CLUES ANY HELP OFF U BEASTY BIKERS Shocked CHEERS MANY THANX
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truslack
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Joined: 08 Apr 2007
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PostPosted: 14:11 - 20 Jan 2011    Post subject: Reply with quote
Okay, a couple of places to start:

First, switch caps lock off.

Has the bike been modified in any way?
Is it running the standard airbox and filter?
What spark plug have you got in, what colour is the electrode, and when was it last changed?
Is the oil pump correctly adjusted?
Have the jets in the carb been changed?
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chris-red
Have you considered a TDM?



Joined: 21 Sep 2005
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PostPosted: 14:41 - 20 Jan 2011    Post subject: Reply with quote
I doubt very much a 25 year old 125 will come up in 2nd.
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 15:59 - 20 Jan 2011    Post subject: Reply with quote
truslack wrote:
Okay, a couple of places to start:

First, switch caps lock off.

Has the bike been modified in any way?
Is it running the standard airbox and filter?
What spark plug have you got in, what colour is the electrode, and when was it last changed?
Is the oil pump correctly adjusted?
Have the jets in the carb been changed?



the bike has a micron short exhaust on her thats the only modification and i not that good with knowlege of bikes just an ok rider ha its water cooled the spark plug i have in her is a BR8 ES the oil pump is correctly adjusted as cms motorcycles told me this whewn the rebuilt the engine the jets and carb is original but fine good infact . i uploaded some pics for you in the attachments so you can check the bike out
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truslack
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PostPosted: 16:03 - 20 Jan 2011    Post subject: Reply with quote
Umm the bike in the picture is definately not an RD125...

If it has a micron exhaust, chances are the main jet should have been replaced with a larger one, ride the bike at full throttle then kill the engine, take the plug out and post a (decent, in focus) photo of the electrode.
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 16:22 - 20 Jan 2011    Post subject: Reply with quote
truslack wrote:
Umm the bike in the picture is definately not an RD125...

If it has a micron exhaust, chances are the main jet should have been replaced with a larger one, ride the bike at full throttle then kill the engine, take the plug out and post a (decent, in focus) photo of the electrode.


lol sorry the image in this pic is thats my pitbike the electrode is fine as the plug was only put in yesterday ummmm some one said about the power bands need turning up or something could this be true
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 16:23 - 20 Jan 2011    Post subject: Reply with quote
Hi

Forget what the jetting changes were for an RD125LC when derestricted, but from memory one of the issues was that one of the fuel circuits could not easily be changed (needed to be leaner at low throttle openings I think).

Derestricted the RD should manage about 87 true (and indicate about 95). It will have stuff all at low revs and I would not be at all surprised if it has a flat spot just before the power band (and likely that a K&N would make that flat spot worse).

All the best

Keith
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mick2011
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Joined: 16 Jan 2011
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PostPosted: 16:24 - 20 Jan 2011    Post subject: Reply with quote
i would get a standard airbox and dump the k&n
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 16:28 - 20 Jan 2011    Post subject: Reply with quote
i have not air filter its watercooled lol
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TQ
Trackday Trickster



Joined: 17 Dec 2009
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PostPosted: 16:38 - 20 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
i have not air filter its watercooled lol


It still needs air to mix with fuel so it'll burn, the air filter keeps this air clean.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 17:02 - 20 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
i have not air filter its watercooled lol


There should be an air filter on the carb. Originally it would have an airbox containing a filter. If this has been removed and replaced with a K&N (or just removed) then it will be running lean. If a K&N has been used then these seem to often cause problems with a flat spot at mid revs. If no air filter has been used then expect to land up wrecking the engine (only takes a small piece of sand to do a fair bit of damage).

All the best

Keith
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 10:23 - 21 Jan 2011    Post subject: Reply with quote
hey folks i looked into the airfilter and its standard apparently no k&n wahoo haha umm can u think of anything else that can increase my power? is the power band/valve adjustable? or anything else? many thanks tom
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 11:04 - 21 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
hey folks i looked into the airfilter and its standard apparently no k&n wahoo haha umm can u think of anything else that can increase my power? is the power band/valve adjustable? or anything else? many thanks tom


Power valve and power band are 2 totally different things.

The power band is the band of revs in which the engine works well. On an older performance 2 stroke this tends to be quite defined, with the power coming in fairly hard at some revs and then fading away rapidly at higher revs (ie, might come in at 7000rpm and die away at 10000rpm). This is because of the way 2 stroke exhausts (and other bits) work. Down side of how they work is that outside their working range they tend to make things worse.

The power valve is normally a valve on the exhaust port that moves the top of the exhaust port (so changing the port timing) or opens a chamber off the exhaust port (increasing exhaust port volume). A lower exhaust port or more exhaust port volume will give more low down power at the expense of top end power, hence being able to change these depending on revs mean you can have you top end power while the power valve can make it rideable at low revs.

Your bike doesn't have a power valve (only the very late RD125LCs had them, sometimes called RDZ125LCs), so nothing you can adjust there.

The power band is the result of how the engine is tuned. You can affect it by changing thing like the exhaust and porting the barrel. Good chance that you will either gain peak power at the expense of low down power or gain low down power at the expense of peak power (or make a mess of it and lose both).

The reason that you often get a flat spot or spluttering before the power band is that the exhaust works by bouncing pressure waves up and down it. These pressure waves move at a constant speed whatever the rpm. At high revs they are timed to bounce back to the exhaust port and back again to suck the next lot of exhaust gas from the engine (and the next lot of fresh fuel / air into the engine). However at lower revs the pressure wave will instead arrive at the right time to try and ram the exhaust gas back into the engine.

How quick is it now?

All the best

Keith
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chris-red
Have you considered a TDM?



Joined: 21 Sep 2005
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PostPosted: 11:05 - 21 Jan 2011    Post subject: Reply with quote
You could trying tightening the power band (not to much as it could snap) or swapping it out for a 'red' one.
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Well, you know what they say. If you want to save the world, you have to push a few old ladies down the stairs.
Skudd:- Perhaps she just thinks you are a window licker and is being nice just in case she becomes another Jill Dando.
WANTED:- Fujinon (Fuji) M42 (Screw on) lenses, let me know if you have anything.
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 11:42 - 21 Jan 2011    Post subject: Reply with quote
hi there keith, right sdo its a powerband i have haha many thanks for ur help i appreciate it right my bike gets to like say 6000rpm kicks in a little bit but not much as it should do i have been told? i struggle to get too 9000rpm wen warmed up my uncle who drives quite alot of bikes said thati should have more torque in first and second which i dont know if it is true the person i broght the bike off said i would be able too get 100mph$ out of her easy soo i hope this helps u work my situation out. and also in 3rd i get to about 6000rpm and i have a splutter till i get to bout 7 half any clues.


oh and chris thanks too u too mate what u mean by red band??
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Paxovasa
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Joined: 25 Apr 2010
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PostPosted: 11:45 - 21 Jan 2011    Post subject: Reply with quote
majortom86 wrote:

oh and chris thanks too u too mate what u mean by red band??


Some people never learn Rolling Eyes
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 11:48 - 21 Jan 2011    Post subject: Reply with quote
what you mean paxova or what ever i not that clever with bikes i only 20 odd and these bike forums r here too hep arnt they?? i really dont know what 'red' one is sorry if i anoyed u
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 11:50 - 21 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
i struggle to get too 9000rpm wen warmed up my uncle who drives quite alot of bikes said thati should have more torque in first and second which i dont know if it is true the person i broght the bike off said i would be able too get 100mph$ out of her easy soo i hope this helps u work my situation out. and also in 3rd i get to about 6000rpm and i have a splutter till i get to bout 7 half any clues.


Suspect the mixture might be wrong, especially the main jet. Check the jetting of the carb against standard for a full power engine.

Stock full power the top speed was 140kmh from memory (so 87mph), but the speedos over read so 95mph indicated was pretty common.

Rear wheel torque is dependent on engine torque and gearing. The higher the gear the less torque at the back wheel.

All the best

Keith
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Paxovasa
World Chat Champion



Joined: 25 Apr 2010
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PostPosted: 11:56 - 21 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
what you mean paxova or what ever i not that clever with bikes i only 20 odd and these bike forums r here too hep arnt they?? i really dont know what 'red' one is sorry if i anoyed u


Stop believing that you can change the colour of the power band. The power band is when the engine produces the optimum acceleration.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 11:57 - 21 Jan 2011    Post subject: Reply with quote
majortom86 wrote:
i really dont know what 'red' one is sorry if i anoyed u


As above. It is a very old joke that you can buy replacement power bands. They are not anything physical that you can buy.

All the best

Keith
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majortom86
Two Stroke Sniffer



Joined: 20 Jan 2011
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PostPosted: 11:58 - 21 Jan 2011    Post subject: Reply with quote
Kickstart wrote:
majortom86 wrote:
i struggle to get too 9000rpm wen warmed up my uncle who drives quite alot of bikes said thati should have more torque in first and second which i dont know if it is true the person i broght the bike off said i would be able too get 100mph$ out of her easy soo i hope this helps u work my situation out. and also in 3rd i get to about 6000rpm and i have a splutter till i get to bout 7 half any clues.


Suspect the mixture might be wrong, especially the main jet. Check the jetting of the carb against standard for a full power engine.

Stock full power the top speed was 140kmh from memory (so 87mph), but the speedos over read so 95mph indicated was pretty common.

Rear wheel torque is dependent on engine torque and gearing. The higher the gear the less torque at the back wheel.

All the best

Keith




the mixture is the the screw which is ment to be 2 and a half turns or what ever i turnt the screw that it was reli spluttery so turned i bk like i tiny bit and it made it loads better Very Happy will this dramatically change the power would it.

cheers tom
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Paxovasa
World Chat Champion



Joined: 25 Apr 2010
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PostPosted: 12:02 - 21 Jan 2011    Post subject: Reply with quote
You could go and get it dyno tested, they will set it up for you.
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majortom86
Two Stroke Sniffer



Joined: 20 Jan 2011
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PostPosted: 12:03 - 21 Jan 2011    Post subject: Reply with quote
Paxovasa wrote:
majortom86 wrote:
what you mean paxova or what ever i not that clever with bikes i only 20 odd and these bike forums r here too hep arnt they?? i really dont know what 'red' one is sorry if i anoyed u


Stop believing that you can change the colour of the power band. The power band is when the engine produces the optimum acceleration.


i did not think it was a colour i thought it may have been a stronger version oor something as iaske if i coul ajust it toi
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majortom86
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Joined: 20 Jan 2011
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PostPosted: 12:05 - 21 Jan 2011    Post subject: Reply with quote
Paxovasa wrote:
You could go and get it dyno tested, they will set it up for you.


thank yu mate
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