2003 Yamaha DT125R tuning

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2003 Yamaha DT125R tuning

I have a 2003 UK spec Yamaha DT125R. So far the only modification I have made is putting a Fresco Big One silencer onto it. This gave me a little extra power but not very much. I am thinking of getting a Fresco expansion pipe to match. I have been told that I will need to modify the carburettor jets if I get a new expansion pipe. Can anyone tell me what I need to do?

I asked my dealer about derestricting it and he told me that the YPVS 'trick' (i.e. turning it 180 degrees) cannot be performed on my 2003 bike. Is this true? If so, what other ways can I get more power out of my bike without going into big money. Would carbon race reeds make much of a difference?

The dealer told me that in order to properly derestrict the bike I would need to replace the whole electronics system on the bike but other people that I have asked have said this is a load of bull. Which is true?

Thanks in advance!

It is not entirely true about turning the powervalve it is possible to do that but you will loose all bottom end power + you will have to disconect servo ect, as your bike is a 2003 model it will already have the powervalve servo and pully it is just a simple case of disconnecting 1 wire as with the TZR125RR however i lent some one the instructions i blagged from yamaha and cannot remember which wire if you haven't found out by tommorrow i will go and have a word with someone in the know.As for the different reeds in my expieriance they don't make a huge difference i put carbon ones in my KR1-S and felt no difference.I'm not convinced you would need to fuck with the jets to much on a two stroke as fueling does not have to be as precise as on a 4 - stroke however it my be an idea to lift the needle up 1 notch.YZ125 engine 'll fit in don'tcha no

If you turn the powervalve it will still be ridable. It will just have a more pronouced power band which is quite good fun in it's self. You might have to rev it a bit more to get it going but we are talking about a 125 here so thats the norm anyway.If you do the power valve and change the pipe I sugget you do a plug chop and check the colour. You dont want to melt the piston, do you? I think you will need to go up 1 - 2 sizes on main jet.Dont bother with the reeds, you wont notice the difference.

Scuzi wrote

I have a 2003 UK spec Yamaha DT125R. So far the only modification I have made is putting a Fresco Big One silencer onto it. This gave me a little extra power but not very much.

Silencer will not have any great effect

Scuzi wrote

I am thinking of getting a Fresco expansion pipe to match. I have been told that I will need to modify the carburettor jets if I get a new expansion pipe. Can anyone tell me what I need to do?

You pretty much must rejet. If you don' then you stand a good chance of seizing the engine. 2 strokes tend to rely on the fuel too do some of the engine cooling. Personally I would say that for engine safety rejetting a 2 stroke is more important than a 4 stroke if you are changing exhausts

Scuzi wrote

I asked my dealer about derestricting it and he told me that the YPVS 'trick' (i.e. turning it 180 degrees) cannot be performed on my 2003 bike. Is this true? If so, what other ways can I get more power out of my bike without going into big money.

I cannot see why, unless the power valve is in place and connected up so that it works, but then set to do silly things at high revs. Does the bike make a "zweek zweek" noise when you turn the ignition on?

Scuzi wrote

Would carbon race reeds make much of a difference?

They will make you wallet a bit lighter which might increase the performance, beyond that next to no effect.All the bestKeith

Thanks for the advice. I'll forget about the reeds for now and go for the new exhaust and jets.

Quote

Does the bike make a "zweek zweek" noise when you turn the ignition on?

It does indeed sir.

HiSounds very likely that it has a power valve fitted. At a guess it is either full power already, or Yamaha have set them up so that the valve closes again at some strange revs. I suspect that zx7tim suggestion is correct. Probably a wire to be connected or cut somewhere (for example the old Suzuki RG125 was restricted this way, and on those cutting the black and white wire to the cdi gave them full power)All the bestKeith

behind the clocks there is a green and black wire put this to earth and instead of peaking around 7000rpm it full go to about 13000 i dod it on my dt125x n f*ck me what a difference and ive been told to change the full exhaust system as thats what is restricitng its full power now. dont bother turning the servo do the wire.

hi can any one help me de restriced my dt125 x sm 2007 model email me at ted4411@hotmail.com please help me thanks

Hi, i have the same bike DT125r 2003 and looking to fully derestrict it, i blew the engine coming down cat and fiddle at 90mph (oops) didnt know the bike was capable of getting to that speed but never mind eh? because i have blown the engine i have had it board out to around a 175cc as the tolerance for the head is about that, yes? or could i go more?... this trick with the cable behind the clocks, is that safe to do so for a 2stroke? sounds a bit risky to me. so all i have done is upgraded the exhaust with a full BIG ONE set up. more questions to ask... what size supermoto rims could i get that would fit my bike? and would YZ125 USD forks fit mine?  Many thanks ,Jake

nicoSPAIN knows the trick

where can I get a raceing cdi unit from ? ive put 170 big bore kit on my dt 125 re 2004 and jetted it up to 240 and earthed the green black wire

In my bike i found some regretting issue with gearbox repairs Coventry  

Hey just need the know what the little hole on the inlet side of the piston does dt125re 2005 isit needed will it fail if it isnt there can some please help ??

Any body's know what cable to earth for the power valve ??? I have a dt125r 1988

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