DT125R ARCHIVE

matt rhoades · DTR Member

dtr 125 1994

SimsonS51E · Guru

You seem happy enough that you have the PV sorted in your mind ?

Does your PV have the servo motor etc to control it via engine speed ?
[looks like yes, from site .. !]
http://dtr125.net/tuningf.htm

Are you still running standard Xpanny Chamber @ front & standard rear ??
If yes to Xpanny, then it sounds like the chamber is holding you back via the insert
http://dtr125.net/tuningf.htm

Why not peg the PV in both open & closed just for a test run, if your happy that in it's closed {low} position, it pulls well @ low revs .. & with PV Open {high port} it slugs down low, but revs it's nads off, at least you will know all ok & that PV positions are as you think ..
If it still wont go as you need, back to Xpanny & poss tailpipe ..
Your exhaust might also be coked up to fook if it's done the miles !!!???

Be careful
& make sure PV is not in a position to hit piston ???
Im not sure if this is possible ??
But am sure Gixxer will post here tonight & tell you if it is poss to get PV so wrong it ****s piston !!!

Gixergav · DTR Senior Member

Oh yes the valve can it hit it.Acts like a guillotine and chops the top corner off the piston.
94 as stock uk bike did not have a servo fitted so its been added at a later date or an import. Is the cdi on yours about fag packet size mounted under the tank?
Is it a standard front pipe?
A 94 with an original pipe is rare so the front pipe could be a later restricted one
Fully open valve should boost you upto 10k so make sure the valve is fully open.Take the exhaust off and look up the exhaust port to check.
Disconnect the servo altogether and manually open/close the valve to see if it helps.
The valve should turn clockwise to open from its closed position

http://www.activeboard.com/forum.spark?forumID=66365&p=3&topicID=25126106

matt rhoades · DTR Member

Okay thanks for both your replies guys. Loving all this knowledge!!!

Firstly the servo works n comes in approx 6k. But im not sure if its because of it being an earlier model but....the servo turns clockwise with revs then returns to closed as it should. The vid shows anti clockwise? Am i being dull or do i need to change the pulleys over. They currently cross one another.

I do have a std xpanny hoping to gut this weekend. And a dep rear can.

Gixergav. I am running a std 56.4 piston n rings so i pressumed i wouldnt strike it?And ive already tried it the wrong way....which gives poke in low revs but but nowt up top end. I had a play with pv today. It comes in earlier but due to what i think is a restricted xpanny it wont get above 8k. Can you buy a NEW cdi for my yr or do i look for a second hander?

Thanks again for the replies gents. AWESOME. Will post some pics soon

Gixergav · DTR Senior Member

If its a stock 94 cdi its derestricted as standard.
Does the servo turn clockwise or the powervalve itself? The powervalve if set right will have to move clockwise as looking from the left of the barrel to open. This should happen at 5.5k-6k.
Unplug the servo and manually open the valve.Take the exhaust off to look/feel up the port to make sure it is fully open.See if will rev above 8k.If not then you know its not a powervalve issue and a problem elsewhere.
The valve if turned the wrong way can protrude into the cylinder and hit the piston.It is possible 'cos i've seen the after effects.Usually if its turned to far clockwise to open it.

ben350 · Guru

TBH I would only expect that to happen on an engine thats been bored out beyond the 1.00mm oversize that Yamaha sell pistons for, maybe the 2.00mm that you can get from Mitaka etc.

Gixergav · DTR Senior Member

No you dont understand.By design the valve can rotate 360 degrees in the barrel. The top most part of the valve can stick out into the cylinder walls and contact the piston if rotated too far.Be it a stock bore or 2mm oversize.
Unable to happen on a servo assisted cos it will only travel so far by the cables.When opened by hand and not checked up the exhaust port if its right or not can lead to contact

SimsonS51E · Guru

Gixergav wrote:

No you dont understand .....

..... can lead to contact

and 'Contact' is the known terminology of the british forces
for engaging the enemy !

Bits of fookin red hot metal flying round, causing untold death & destrucion !

RGV anyone ?

ben350 · Guru

I will beg to differ - none of my DTR power valves have ever touched the piston on when rotating them by hand / turning the motor over.

The RGV uses a completely different PV design = its crap!

Gixergav · DTR Senior Member

Probably 'cos you didn't place the valve in the spot where the piston hits it

ben350 · Guru

Next time you have the cylinder off have a look down it and turn the YPVS bobbin round - you wont see it protrude into the cylinder.

Gixergav · DTR Senior Member

The point just before the piston contacts the valve.Now don't get me wrong its not a dead hit and it stops.You can feel the piston push against the valve as you move the piston up the bore.In a running, expanded through heat motor this WILL cause havoc.

The valve in this barrel has already kissed a piston at some point

matt rhoades · DTR Member

Gixergav. Youve got me all paranoid ere mate hmm

What do you mean when you say "you didnt place the valve in the spot where the piston hits it"? I was under the impression it could only be turned 180deg closed or open.

I know i have fitted it incorrectly first time after the re-build cos there was no top end at all. Turned it 180 and it was fine..powerband after 5000ish. And totally different sound to the engine. Is there a chance ive done some damage?

I dont think mine has struck cos sureley i would've known all about it?

Sorry for all the questions again matey smile

Gixergav · DTR Senior Member

No you haven't hit the piston 'cos your motor won't be running at all if it had.
The valve is either in its 'closed' position, which is when the valve covers around half of the exhaust port.This gives strong bottom end with power that tails off at around 6k
When the valve is rotated clockwise it becomes 'open'.The exhaust port becomes fully open and gives low bottom end power but a powerband at 6k and revs right through to 10-11k
If it turns too far clockwise you can contact the piston as shown on the pictures

SimsonS51E · Guru

Gixergav wrote:

No you dont understand .....

...... can lead to contact !

Handbags at Fookin' Dawn Boys !!!!

Ps .. Nice Piccie GiX ...

ben350 · Guru

No handbags here mate

SimsonS51E · Guru

Manbags ?

SimsonS51E · Guru

Gonna keep my opinion on PV's getting Twa*ted, until iv'e had top end off mine !

but photo's deffo got a ding from summat ?!

-- Edited by SimsonS51E at 18:53, 2009-02-27

ben350 · Guru

My opinin is just that an opinion, I dont try and start flame warrs on the internet unlike you get from some drongo's on other forums - I'm more than happy to have a healthy debate on a subject and if its proven that I'm wrong I will admit it.

-- Edited by ben350 at 20:36, 2009-02-27

Gixergav · DTR Senior Member

I'm not teaching anyone to suck eggs here guys i'm just trying to pass on the knowlegde of what i know about bikes and the Yam 2 strokes in general.I've been round enough to pass on some wisdom but i certainly don't know everything about 'em.
I dont want people to shag their bikes up if i can help 'em.Bikers like, y'know.
I admit i don't know everything about bikes and at times we all have to sit down and listen to someone more experienced but thats how we all learn right?
Anyway crack open the beers,pass the dutch and enjoy the site!
We are all here for the same reason eh?

ben350 · Guru

Here here!

SimsonS51E · Guru

I Concur ...

Flame Warrs ??

Sounds fookin' exiting mind ?

No, we don't seem to go for that $hite here, far to civilised

Reet, im off to MCN forums for some Flamin' ......