There must be more information on the web about the powervalve than there are women with their t1ts out. okay, maybe not, but theres a lot and not all of it agrees with itself!!
I was wondering if anyone could shed any light on my problem.
I've just got a '94 DTR and its now my favourite toy (and it shares a garage with a 125bhp/160mph sports bike)!
When I got it it had nothing below 6.5k revs and went like a bat out of hell over this...but the revs ran out dramatically at about 8.5k. 2k worth of revs isnt a lot to play with when you are trying to fit into traffic.
So I did a little research, and took it apart, looking in from the exhaust port there is a slight score on the bore, fractions of a mm but still there so it'll not be perfect I accept that. The first thing I did was saw that the cables from the servo were crossed so uncrossed em so now during the cleaning cycle on first switch on it moves anti clockwise about 80 deg and then back to in line with the alignment holes. This ran brilliant at low revs but wouldnt get past 6k at all. So I turned the powervalve through 180 degrees, took the exhaust off and made sure that at rest the valve was fully open and the cleaning cycle closed it off and then opened it back up. This now runs okay but there is still nowt above 8k and no real sense of it coming 'on pipe' at 6.5k like it had when I first got it - Oh its got a DEP pipe by the way.
Now, I then read on the powervalve installation instructions that this year of bike should have had the servo cables crossed after all. But... how the bollox would that work cuz this would close the valve after 6.5k??? Also, the cleaning cycle would be clockwise then anti-clockwise (not as per the instructions). If I re-crossed the cables and turned the valve through 180 this might work but then the 'missing' part of the powervalve would be at the top of the exhaust port and I thought the whole idea was to lower/higher the exhaust port to control the timing of the exhaust pressure waves.
Any help would be received with much gratitude. The main things are probably...
1. Which way up is the PV is meant to be on this year of bike i.e. chunk missing from top or bottom? or put another way, is the PV meant to close off the top or bottom of the cylinder side exhaust port at low revs.
2. I only get max 70mph top end, considering the bore scoring is this reasonable?
3. With the DEP pipe and powervalve fully open, should I be expecting the power to make it all the way to the red line or is it normal that it starts significantly dropping off the power after 8k?
**** I can go on a bit, soz.
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The valve has the cutaway at the bottom. When the revs are low it positions itself to make the port lower. When the revs increase it turns anticlockwise when viewed from the left side which has the effect of raising the height of the exhaust port.
Cant help you with the cables as ours has the power valve fixed and yes the performance is as you say with a DEP pipe - comes in with a bang. However, with a correctly operating powervalve it should be smoother than that for your bike. There is a download of a Haynes manual on this site so download it and see what it says about setting up. There is also a genuine Yamaha manual that can be downloaded from the DTR125.net website. That will help you get it set up.
You should get more revs though. Take it out for a blast and then do a plug chop at full bore and have a look at the plug colour. Should be a nice tan colour. There is a chance that you are running weak with a DEP on board although the official recommendation is that standard jetting is ok. In terms of the score in the bore - do a compression check. Correct combustion pressure is about 102 psi. Good luck.
Welcome madmark, i've just been having a look through my haynes but it doesn't seem to mention anything about the PV on pre 1997 DTs. Anything after 1997 and the cables for the PV are uncrossed, sorry mate not really that useful to you i guess.
Dingle am i being daft here, surely DT's before 1997 had servo assisted power valves?
Out of interest madmark, how come you've bought a DT when you have a sports bike, surely it will feel soooo slow :)
Out of interest madmark, how come you've bought a DT when you have a sports bike, surely it will feel soooo slow :)
I know plenty of riders who have both a large capacity bike and a little 2 stroke bike for fun, its because the smaller 2 strokes may not be as fast, but they are light, flickable, and a hell of a laugh!
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Got it in one Mammoth. Your really have to take your brain out and go for it on the sportsbike, you have to be doing a hundred and silly miles an hour for it to make any sense. So the DT is a breath of fresh air.
I got the DT because I broke my leg 3 weeks ago on a mountain bike and the modern brace thing is set to bend up to about 70 degrees so I can just ride the DT but couldnt get close to the sports bike at first. I can now bend enough to fit the bigger bike but the DT is so manueverable and you can still give it welly round the corners. It also keeps you on your toes more cuz you cant just blast past whatever's in your way
I just got a haynes today and I've downloaded the manual from the main site, I suppose my problem is in getting the info for the right model, if I use the '88 manual it has the wrong carb (mine is the flatslide) but the other manual isnt supposed to start till 04. No worries though, I live in the garage so as soon as the leg is mended I'll strip the DT fully and do a complete re-build.
Cheers for the help though.
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If you look in the 'useful links' thread where the haynes manual is... I'm sure it covers both the older style, and then the newer models toward the end?
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You are one person, out of 7 billion people. On one planet, out of 8 planets. In one starsystem, out of 100 billion star systems. In one galaxy out of 100 billion galaxies
Got it guys, thanks for all your help. Dunno why but although its a '94 the cables need to be straight (1 to 1 and 2 to 2). I arsed around with all combinations and finally found out that it was just poorly adjusted. I set it to line up the tangs with the hole to the rear of the powervalve housing. nah, it needs to be further to the left than that. 75-80mph and kicks in rather nicely at 6.5k and can hold top all the way from 30 to the top. Chuffed to bits, must go practice wheelies. Cheers.
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