De Restricting my DT125R

[Guest MaD.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!

When i swapped one from a 88 to a 97 theres was a very noticeable difference in performance, the bike performed alot better. Some big changes happened to the DTR in/around 96-97 in regards to the restrictions, and from what i have read since the CDI was one of them.

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!).

One mysterious silver/grey box

Restricts the revs to around 7500rpm(before the power band kicks is) And is fitted mainly to German bikes and is an easy fix.

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.

We will see just what is in there in the next week or two, when i cut my spare open.

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!

Interesting, i don't suppose you have any pictures of this circuit board ?

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.

The only significant change there would be the power jet, with it being a basic journal/passage within the carb body and not a replaceable brass part like the other jets. Do you know this to be 100% ?

I have read somewhere about changing carbs on later models and this could be why

Vez

[Deeteemx]

Interesting, i don't suppose you have any pictures of this circuit board ?

The only significant change there would be the power jet, with it being a basic journal/passage within the carb body and not a replaceable brass part like the other jets. Do you know this to be 100% ?

I have read somewhere about changing carbs on later models and this could be why  

Vez

Sorry Vez, I haven't got any photos of the pcb at the moment, and don't know how to attach them to the thread (as you've already noticed, I'm still learning how this forum works!)

I discovered the pcb in a speedo I have that broke apart in an accident. Its quite an elaborate affair with lots of micro electronic gubbins attached to it. It may just be there to operate the temp warning light....or it may be something more sinister?!!

The Haynes manual gives detailed specifications for the 1989-98 and 1999-2003 carburettors, and I don't doubt their accuracy (although I haven't checked them). The manual says the power jet increases from a '60' on the earlier carb to a '95' on the later one. I think this jet is probably in the float bowl, near the bottom of the vertical passage that runs down the side of the carb.

[Guest MaD.VeZ]

Sorry Vez, I haven't got any photos of the pcb at the moment, and don't know how to attach them to the thread (as you've already noticed, I'm still learning how this forum works!)

I discovered the pcb in a speedo I have that broke apart in an accident. Its quite an elaborate affair with lots of micro electronic gubbins attached to it. It may just be there to operate the temp warning light....or it may be something more sinister?!!

The Haynes manual gives detailed specifications for the 1989-98 and 1999-2003 carburettors, and I don't doubt their accuracy (although I haven't checked them). The manual says the power jet increases from a '60' on the earlier carb to a '95' on the later one. I think this jet is probably in the float bowl, near the bottom of the vertical passage that runs down the side of the carb.

Shame about the pcb pics, i expect something sinister, and i think it may have something to do with the black/green wire or where the black/green wire should have gone to.

The power jet is indeed in the float bowl, the short pipe that connects the top half of the carb to the bowl is part of the power jet circuit, but there are no replaceable jets in this circuit that i have found. I have had it block in the bowl before so i'm very familiar with it.

As for posting pictures, i'm uploading a video as i type, to help people out because there has been alot of questions recently about pics, there is a faq and i will and the vid to the info already there.

http://www.yamahaclu...sting-pictures/ < faq

Vez

[Airhead]

Next job to do is replace my 3BN cylinder head with a 3MB version.

3BN

3MB

Needs re painting but not in too bad condition, just a bit of metal debris in the squish, nothing that a rub down wont fix. I was asking about the strange squish area with the 3BN head, Phifi of the French forum Yam2stroke, told me it is to meet noise control standars and to limit detonation? I know...there shouldnt be detonation

[2 Wheels]

So its just another way of slowing the bike down (restriction)

Me is gona keep an eye out for one of these heads !

Your a mind of information OGit

Fair play

[AndyDtr08]

Thats the head from an early to mid 80's LC isnt it? I think i have a spare one of them, ill have a look when i sort my parts, might be worth putting on my 2002.

Also, the bottle that causes restriction near the carb. Presumably we aren't talking about the YEIS bottle? It's the one that sticks off sideways between the airbox and the carb. This will have the same affect if removed from a dtre?

[Airhead]

Me is gona keep an eye out for one of these heads !

Dont buy unless the combustion area is good, mines not perfect but some of them are in a terrible state from detonation and on ebay some unscupulous sellers may just post a pic of the top...YOU!! have to ask the right questions.

Thats the head from an early to mid 80's LC isnt it? I think i have a spare one of them, ill have a look when i sort my parts, might be worth putting on my 2002.

Early LC's had a black painted square shaped head...quite different.

This was off a DTRE they have been fitted to many bikes, TZR's TDR's DTR's as far as i know

[satelliteone]

oooooo.. just found this thread..My DTR compression is high, the lip near the squish area.. on the 3BN has ben taken off..But i have encountered a problem.. it keeps blowing head gaskets. I wonder the 3MB version would help.

Yam have said there are diffent head gaskets!

The TZR RR model has a higher compression, i would love to know what head it uses. I got a feeling the 3BN design was for the lower compression DTR engines. Also the TZR RR uses the 32mm carb. unlike the 26mm mikuni..

any way brill thread guys!.. love it..

PS.. my new cookoo clock! well DTR bottom end, ive built..

PS2.. got some interestin info for ya guys regarding over sized pistons and PV`s.. not good!..lol

[Airhead]

I got a feeling the 3BN design was for the lower compression DTR engines.

Well the 3MB and the 3BN heads have both been used on DTR's at some stage.

Scrubbed up well, just need a gasket set now, and some time, and a sunny day!

[satelliteone]

i got a feeling, the squish band on the 3bn head is trapping compression, u think that my head has 1mm taken off. the piston is quite close to the douhgnut area. gases are pretty squished in the recess. probs explain why gaskets go pop quit a bit.

lookin out for a 3mb head now. i need 13:1 compression...

also been looking into better head gasket design, bout to talk to these guys. custom made!

http://www.ferriday.co.uk/copper/copper.shtml

[AndyDtr08]

I think ive got a 3mb in the loft. Pretty sure i saw one the other day when i was getting a mudguard down.

[gettingbackintoit]

Dont buy unless the combustion area is good, mines not perfect but some of them are in a terrible state from detonation and on ebay some unscupulous sellers may just post a pic of the top...YOU!! have to ask the right questions.

Early LC's had a black painted square shaped head...quite different.

This was off a DTRE they have been fitted to many bikes, TZR's TDR's DTR's as far as i know

hi og just joined up tonight, over the years ive had 125dx,200dx,400dx,350lc anyway ive just got hold of apair of dt engines to build a fast little project for my son, first question lol whats the differance between a y-1 head and a y-3 head of which i have both, ive read lots of posts but not came across the later any help would be greatly app

kind regards nick

[Airhead]

hi og just joined up tonight, over the years ive had 125dx,200dx,400dx,350lc anyway ive just got hold of apair of dt engines to build a fast little project for my son, first question lol whats the differance between a y-1 head and a y-3 head of which i have both, ive read lots of posts but not came across the later any help would be greatly app

kind regards nick

Well i'm learning all the time Nick, My 3BN head is a Y1 and my 3MB is a Y2, so I am keen to know what you have there any chance of photos top and bottom of those you have, I am not a DTR expert got mine in January this year and have learned a bit already.

Welcome to the forum.

[gettingbackintoit]

Well i'm learning all the time Nick, My 3BN head is a Y1 and my 3MB is a Y2, so I am keen to know what you have there any chance of photos top and bottom of those you have, I am not a DTR expert got mine in January this year and have learned a bit already.

Welcome to the forum.

i will get some pics as soon as i work out how lol, please bear with me

[Airhead]

i will get some pics as soon as i work out how lol, please bear with me

For pictures see FAQ's

[Airhead]

Today I fitted my 3MB head.

Took the plug out of the old head and it's a nice colour (crap picture)

On looking at the two heads I estimated that the 3MB head would offer higher compression. With the 3BN and a warm engine got 95psi

and with the 3MB my suspicions were confirmed with 105psi and thats cold so would increase with a warm engine.

All in all its a complicated job compared to the DT175 air cooled, torque settings of head bolts can only be done on some of the nuts due to access problems, Ring spanner and guesswork for the others. Before you ask yes it ran sweet going home a trip of 7 miles but taking it easy due to having drained the coolant and uncertainty over whether its working properly. The temperature sensor in the new head didnt work but the radiator was warm when I got home so thats good. Also the head gasket fitted was a pattern one so that may or may not be a source of trouble in the future.

New head, new plug

[2 Wheels]

Aye, OG

An extra 10psi thats gotta be good/better.

So she is still running sweet, eh ?

Good job !

[gaterade0]

Cheers Pat, There are several schools of though regarding the YEIS 'boost bottle'

1; To tune your bike up take it out, it's Yamaha's underhanded attempt to restrict your bike.

2: To tune your bike you need to fit a 'Boost bottle' as developed by Yamaha back in the 70's

i'm with 2:, I dont believe that Yamaha would have developed these things and continued to fit them to their bikes with extra production costs if they are of no benefit, they certainly were developed as a tuning aid, never as a restriction. The benefit may be small, even un measureable but i dont believe they are detrimantal.

The silencer is a different type altogether, its just a perforated tube with exhaust packing, quite commonplace. But the original is a different story, it is full of tubes to divert the exhaust gasses this way and that before it exits, there is a name for it that escapes me at the mo (its my age y'know)

I would recommend you buy new or used another rather than mess with the one you have.

Vez will post pics but havent taken any, it was going dark when I finished. As for the stickers yes i phoned them and they are all like that now so i'm past caring, still looks good.

hello i wouldnt recommend taking the boost bottle off as i did this last year and my dt125r was really slow spent 3 hours messing with it to put the bottle back on the power was back to normal

[Airhead]

Snorkeling but nor gwttig wet!!!

A lot of people feel it's the thing to do to remove the airbox inlet snorkel in the hope that somehow this will allow more air in to the airbox, the downside to this is increased induction nose and an unlikely risk that should water somehow find its way under the seat, then it will enter the airbox and possibly the engine.

I tried this myself for a while but wasnt really happy with the arrangement. I learned that the snorkel from a DT230 lanza had a different snorkel with a larger inlet (No shit sherlock )

So I promptly ordered one and fitted it today happy with the peace of mind that it cannot possibly restrict airflow...its big! and also happy that should a sunami hit the A57 my bike wont drown

Its quieter too.

[Airhead]

Look what postie brought