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De Restricting my DT125R

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So I just read through this thread and I have a quick question. I have my 175's exhaust off at the moment and I'm wondering if this would be a worthwhile thing to do while I'm waiting to get the barrel back. On my '79 would it just be a matter of getting off the piece in the exhaust and upping the jet, or is there a lot more too it then that?

thats all cameron, I used a dremel and a cutting wheel, you'll need a small diameter one in order to gain access, wont need to jet up much if you are on a 130 try a 140...see how it goes.

I wouldn't bother with a rear braided hose mate, didn't make alot of difference on my 97, the front on the other hand made a huge difference. But i guess your going for looks aswell as performance. Got a link to some somewhere ill post it when i find it if you like.

Thnx VeZ

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Guest MaD.VeZ

Goodridge £23.99 each for either zinc or stainless banjos

http://www.goodridge...ines/yamaha.htm

Venhil £22.32 each chrome banjos £34.07 ea Stainless banjos < swivel banjos for easier routing, not sure if the Goodridge have them, the ones i got second hand didn't but was a few years ago now

http://www.venhill.c...ike_brake_lines,_clutch_lines_&_cables/YAMAHA/125/DT

Oh and good luck finding a pair of Renthals you like, so many variations of the 7/8 bars.

Vez.

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Main reason i kept stock bars as they wasnt bent and i wasnt sure on what bend of bar id like as i didnt have any way of trying any out :(

@OG, arnt you going to bother with the DEP header? I felt it made a huge difference, how about a tail tidy and some nicer indicators?? :D

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Guest MaD.VeZ

Main reason i kept stock bars as they wasnt bent and i wasnt sure on what bend of bar id like as i didnt have any way of trying any out :(

@OG, arnt you going to bother with the DEP header? I felt it made a huge difference, how about a tail tidy and some nicer indicators?? :D

The expansion chamber on DTR's have very little in the way of restrictions in them compared to the DT125RE. In my experience it makes very little difference when you fit an after market expansion chamber to a DTR compared to fitting one to an RE.

With the restriction removed from an DTR expansion chamber as OG has done, there is very little to gain in the way of performance by adding an after market one, only an improvement in looks if you happen to dislike the original.

Vez.

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hi, did the dep silencer make any difference in preformance and sound??

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hi, did the dep silencer make any difference in preformance and sound??

Yep. slightly better performance

Much better sounding

Better looking too!

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Yep. slightly better performance

Much better sounding

Better looking too!

How much was the dep silencer?

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How much was the dep silencer?

I cant remember for sure Andy. i bought it along with the boyesen reeds and a main jet and all i was given was a crappy credit card receipt, But i think it was around £85 anyway ring Manchester Xtreme for a price, thats where I bought mine.

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I'm new to this site and just been catching up on some of the chat. I know its a bit late, but the following may be of some interest to OG and his slugish DT.

I've rebuilt/restored/repaired and derestricted loads of DT125R's over the past 6 years and I can't help noticing that there's seems to be a lot of guesswork on this thread!

Up to 1997 the exhausts were only restricted by the cone in the manifold area that OG removed months ago. These exhausts can be identified by having 3MB...stamped on the front part of the expansion chamber. After 1997 the cone was not fitted, but the exhausts have a big restictor welded into the main expansion chamber instead (near the 2nd bend where the exhaust bends upwards). These exhausts can be identified by the code 3RM...stamped on them.

There always seems to be lots of speculation on internet forums about older CDI's giving more performance, but in my experience they make little difference.

Also, the bottle fitted to the side of the carb intake hose is indeed a restrictor (only fitted to bikes from 1998). Blocking it off, or fitting an earlier airbox to carb hose does give a small improvement in performance.

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There always seems to be lots of speculation on internet forums about older CDI's giving more performance, but in my experience they make little difference.

Fit one from a late 80's DTR to a newer model and you may change your mind ;).

The most likely cause of OG's lack of power (that nobody has mentioned) is an incorrect powervalve setup. I have worked on lots of DT125R's that have the pulley wheel fitted in the wrong position on the powervalve (to restrict the bike for the UK learner market). Some are fitted upside down, but more often the end of the powervalve has a diamond shaped lug for the pulleywheel to fit on to, allowing a choice of 4 positions.

To check that the pulleywheel is located in the correct position, align the "U" on the pulleywheel with the hole in the back of the housing. This should be the powervalve fully open position. Then simply take off the exhaust and look up the exhaust port to check that the powervalve is fully open. If it is not, undo the single bolt and remove the pulley wheel, then refit it in the correct position.

If the powervalve is fitted incorrectly, this simple fix will transform the bike and give it an immediate 15-20 mph boost.

Please see page 1 as it has been done. Around post #32

Also, the bottle fitted to the side of the carb intake hose is indeed a restrictor (only fitted to bikes from 1998). Blocking it off, or fitting an earlier airbox to carb hose does give a small improvement in performance.

I don't think OG has one of these, but i do on my DT125RE and noticed a little difference when i blocked it up, although my bike wasn't fully de-restricted so i do tend to agree with you. But i believe it came in later than 98.

And :welcome: to the forum. Always good to have another DTR fan in here B)

Vez.

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Being doing some research on the CDi's, On your model OG the cdi is apparently restricted in one of two ways ( i don't expect you to want to do any of these its more an info post).

The wires running from the box in-front of the 2-stroke tank ( IF its not a CDI ) would have to be switched around.

There should be a red, yellow, blue, and green wires coming from it, and these are the wires that are switching the cdi.

The red goes to a brown at the regulator.

The yellow goes to a red/white on the pulse coil.

The green to red/white at the CDI

The blue into a plug where the yellow runs from.

To remove the restriction:

Disconnect the red and blue and isolate them.

Join the yellow and green wires together.

Then join the 2 red/white wires together.

This should completely remove the restrictions on the CDI.

---------------------------------------------------------------------------

IF the box is a CDI then the only way to remove the restrictions is by fitting parts from a pre 97 model. (probably the case with yours OG)

These parts are:

Complete wiring loom

CDI Unit, to fit a 3 wire servo unit

stator plate

flywheel

and a 3 wire PV servo

ignition switch (probably work around this)

light switches (probably work around this)

(also mention of the carb, but i can't see why)

-------------------------------------------------------------------------

Imo the second of these two is a little over the top for what difference it would give and i have only posted it in-case any one else comes across this post and has the parts to do it.

This is, I believe is also the reason you have the partially restricted exhaust 3MB :)

(also there is a cat in my exhaust thats a pain to remove but is possible, will get some pics up on a different thread when i do it)

Vez.

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(also there is a cat in my exhaust thats a pain to remove but is possible, will get some pics up on a different thread when i do it)

Vez. 

I find leaving a tin of sardines in close proximity to the bike usually pays off ;):D

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I find leaving a tin of sardines in close proximity to the bike usually pays off ;):D

:lol::lol:

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Please see page 1 as it has been done.  Around post #32

And  :welcome: to the forum. Always good to have another DTR fan in here  B)

Vez.

Oops, still getting used to the forum and didn't notice the thread went on to a second page! Whatamistakatomaka!! I've edited out the "preaching to the converted" bit now.

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Fit one from a late 80's DTR to a newer model and you may change your mind   ;).

And  :welcome: to the forum. Always good to have another DTR fan in here  B)

Vez.

I did swap CDI's once (between a 1989'ish model and a 1996'ish) & didn't notice any difference. Of course it's possible that one or both bikes did not have their original CDI's before I swapped them!

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I don't think OG has one of these, but i do on my DT125RE and noticed a little difference when i blocked it up, although my bike wasn't fully de-restricted so i do tend to agree with you. But i believe it came in later than 98.

And  :welcome: to the forum. Always good to have another DTR fan in here  B)

Vez.

The restictor bottle on the side of the carb to airbox hose started being fitted to some DT125R's from 1998/99 but I agree that not all DTR's had them for the first 2 or 3 years. I've seen some that just had the mounting lug (for the top of the bottle) welded to the frame but no actual restrictor bottle. Not sure if the bottle had been removed by previous owners and the intake hose replaced with an old type version, or if the bikes were supplied like that from new.

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Being doing some research on the CDi's, On your model OG the cdi is apparently restricted in one of two ways ( i don't expect you to want to do any of these its more an info post).

The wires running from the box in-front of the 2-stroke tank ( IF its not a CDI  ) would have to be switched around.

There should be a red, yellow, blue, and green wires coming from it, and these are the wires that are switching the cdi.

The red goes to a brown at the regulator.

The yellow goes to a red/white on the pulse coil.

The green to red/white at the CDI

The blue into a plug where the yellow runs from.

To remove the restriction:

Disconnect the red and blue and isolate them.

Join the yellow and green wires together. 

Then join the 2 red/white wires together.

This should completely remove the restrictions on the CDI.

---------------------------------------------------------------------------

IF the box is a CDI then the only way to remove the restrictions is by fitting parts from a pre 97 model. (probably the case with yours OG)

These parts are:

Complete wiring loom

CDI Unit, to fit a 3 wire servo unit

stator plate

flywheel

and a 3 wire PV servo

ignition switch (probably work around this)

light switches (probably work around this)

(also mention of the carb, but i can't see why)

-------------------------------------------------------------------------

Imo the second of these two is a little over the top for what difference it would give and i have only posted it in-case any one else comes across this post and has the parts to do it.

This is, I believe is also the reason you have the partially restricted exhaust 3MB  :)

(also there is a cat in my exhaust thats a pain to remove but is possible, will get some pics up on a different thread when i do it)

Vez. 

I've seen a similar article refering to this mysterious "silver/grey box with 4 wires" that is apparently fitted to some 1997-99 models....but I've never come across a bike that actually had one fitted (and I've worked on a LOT of DTR's!).

ALL UK DTR's were originally sold with restricted exhausts (to comply with the 12hp learner laws), the earlier models had the cone at the manifold, the later "3RM" models have a restrictor in the expansion chamber. Although the DT125RE has a cat, their exhaust seems to be generally less restricted as this model normally performs well with just the green/black wire being earthed.

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From what i have read about the reed switch, it "retards" the revs at around 7000rpm. I may be wrong but i believe taping it out of the way is only 1/2 doing the job as i think it needs to be earthed to the frame. I noticed a great difference after earthing mine, but then i never tried just taping it out of the way. might be worth an experiment.

Anyone take a look at my thread in general and have anything that would be of any use? Any emails/contact would be fantastic, even if it were stuff i already know, just to put in my workbook and show that ive contacted people.

*EDIT* Also thought id ad, i dont know what my revs are so i cant comment on that as there is no counter, just a speedo that lights up in blue in the dark. OOh la la ( just cos it looks nice IMHO, not cos its french, cos its not..... Its a dutch import!)

The DT125RE from 2004 wasn't fitted with a reed switch....although they do have a very strange printed circuit board contraption inside the speedo!

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I have looked at my carb, there are no markings on mine either only the name Mikuni.

My engine no starts with 4BL.........

My frame no starts with JYA4BL..........

On the left side of my piston barel there is 3MBOO stamped.

I talked to a mate of mine and he said that the standerd main jet changed from 210 to 240 from the year 1999 onwards.

So maby you are right Oldgit

When I had my carb off for cleaning ages ago I prob did look at main size but for the life of me I cant remember what the hell it was.

Some carbs do have the ID mark printed (in black) just above the tickover adjuster screw. Older carbs don't seem to have it (or maybe its just faded away with age) but many of the later carbs that I have seen do have it.

Carbs from 1999 to 2003 (3RME models) do indeed have a 240 main jet as standard, instead of the earlier models 210. According to the Haynes manual they also have a different pilot jet, power jet, starter jet and float height.

Many people upgrade to a 240 main jet (pre 1999 models) when they fit a full performance pipe, but most don't bother when they simply upgrade the tailpipe.

I think all 1999 - 2003 models have frame numbers starting JYA4BL... and engine numbers starting 4BL...irrespective of whether they are an import or a UK model.

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