DT125R ARCHIVE

In fact many race ypvs bikes run without servos and just bolt the powervalve open.On a track using high rpm its a pointless feature and adds weight.

Quote ...
Some say it restricts the ignition/CDI, making it retard the timing at high rpm (Stan Stevens) Others report it allows the ypvs not to close at high rpm therefore keeping the exhaust port fully open. Which is true???

Stan Stephens is right ...
It's a restriction by the YPVS which if not grounded out will not let the Power Valve work correctly / efficently at revs over set level of high RPM
So Because your bike [and mine .. also 04 RE, also all 04 to 08 bikes RE & X]  is designed to be heavily restricted [HUGE HONEYCOMB CAT' CONVERTER in your Xpansion chamber ...]
Waste of time having expansion pipe with huge cat spoiling flow ..

 The power valve system has to be made to work properly by Yam  .... more restictive exhaust = slower bike ... so more restrictive exhaust + Power Valve working as it should = same power as old UN-CAT bikes .. EuroCrats  Happy ...

But if the valve which in working properly, has given you good acceleration & power up to set level of revs ... is left to go full open for port tuning ... the bike would push up to 20 HP [it's a restricted 125 ,,, can't allow that !]... So the PV shuts down at high revs & keeps the bike at 60 ish !

Ground the wire .... PV works ... revs ... but ... exhaust xpansion chamber still restricts bike, as it's full of massive Cat !
 
Dump front of exhaust ... fit dep etc .. now cat gone .. xpansion chamber now works as should [Scavenging wasted Petroil mix, which would be wasted] 
Ideally full DEP, but the front Xpanny is the important bit to fit.. it's not about noise, it's about scavenging, by means of the backwave [timed bounce] see websites about how xpannys work ..

http://en.wikipedia.org/wiki/Two-stroke_cycle

http://en.wikipedia.org/wiki/Expansion_chamber



Restriction in Reed valve block now holds bike back a bit ...
Chop reed block .. [all of this is in the de restrict section of the main dt site !!!]

Now bike fully de restricted ... not done mine yet, but when i do will give you a figure from the Seat Of Pants Dyno ! ... but expect 21 to 24 HP ..

Sat up in wind trailie / knobblie tyres waste power too but  ... 22 hoss = 90 mph ish on a cold day, with a tailwind !

The YPVS actually alters the exhaust port Height / shape .. and you do need it for best performance on a road bike ..
Race Bike ??? Mebbe not ?? Dunno ?? Did Sheenes bike have PV's ??
The rotary valves were for induction not port tuning ?? I dunno ??

Gix / Baz ????????

You could port a bike for high power @ high revs .. but bottom end $hit ..
YPVS leaves you with high fast flow exhaust port, but lowers the port exit, which gives you decent bottom end AS WELL .... Win ... Win .... HUh !

BOTTLES CONNECTED TO INTAKE ... ????

The big one over the engine [they have to be over the head / barrel to work ... it's that fecker called gravity assistance ... !] ....

Is a boost bottle... do not block it off !!!! NOT RESTRICTOR .......

See ..... How does a Boost Bottle improve performance? Air rushes thru the carb on the intake cycle. Ignition accelerates the piston down, forcing the reeds to snap shut. The momentum (inertia) of the air has to go someplace. It goes back thru the carb causing a double rich mixture. The result can be rough idle or hesitation. Due to the high velocity of the fuel air mixture through the carb boot, we need to take advantage of this momentum/inertia energy. The Boost Bottle and tube provide storage for the fuel air mixture between carb boots. The energy (pulse) forces the pre-atomized mixture in the tube from the previous cycle into the adjoining carb boot where the reeds are just opening and ready to receive the fuel air mixture. The boost bottle and tube provide a "boost" supercharge effect to each cycle.The boost bottle is most effective at lower and mid-range rpm, and, when you are on & off the throttle. It assists in filling the cylinder (shorter distance) for a fraction of a second until the carburetor venturi gets enough velocity to fully atomize the fuel. The advantage is that it brings up the torque and horsepower in the bottom of the rpm range, up to where the pipe(s) starts to work. There is a small benefit at high rpm's. What Size? Singles = usually the CC of one cylinder or larger. 700cc Twins = 300cc boost bottle. 700cc Triples = 225cc.

http://images.google.co.uk/imgres?imgurl=http://static.flickr.com/1301/1305891834_4265b2b565_m.jpg&imgrefurl=http://wikiscootia.wikidot.com/boost-bottle&usg=__3izr53BFwpCAJe6pziTNA9hwgoU=&h=193&w=240&sz=9&hl=en&start=12&um=1&tbnid=dUEzG8jIwXNO4M:&tbnh=88&tbnw=110&prev=/images%3Fq%3D2%2Bstroke%2B%252B%2Bboost%2Bbottle%26um%3D1%26hl%3Den%26rls%3Dig%26rlz%3D1W1GGLR_en%26sa%3DN

THE OTHER ONE ... ???

It's near the frame by your N/S [left] Boot  ?????????
Dunno what that does yet m8 ... I have only had bike coupla weeks ...
But i will find out ... or you guys can tell me what it is ???
But i wouldn't block it off yet ?? 

.......

There is some right knackers talked about 2 strokes ...
But if you fit a bigger jet, you will get a richer mixture ... a richer mixture means less heat and LESS POWER ...
Ther Leaner you go [to the perfect petrol air mix level for combustion] ... which is less petrol in the mix ... the more heat you will create & THE MORE POWER YOU WILL GET ...But too Lean = Too much power = You will seize your engine .. too hot see !

Bored of typing now !

 Xtopher ..... Post some pic's of your 04 'X' m8 ...

This $hite is just my personal opinion [which changes over the years !]
and if any of it is crap ... please feel free to discuss ... ???!!!

-- Edited by SimsonS51E at 19:05, 2009-01-14

-- Edited by SimsonS51E at 23:07, 2009-01-14

Gix ..

PV's on race bikes ??

Dump em .. less weight, less aggro .. [espec' Crappy RGV ones (& Prilla, same motor) Like fookin hand grenades by all measure !! LOL !!]

BUT ... Low down drivability & power out of slow bends ?? [as in Ducati Superbikes !] ???

Feck em ... Still dump em & fit more gears... bikes now always got a gear, to keep it in the power range [Band] .... out of any given bend at any given speed ....
Job's $ucked mind ... if you try to pull out of a bend in the wrong gear !!!! LOL !!!!

It's why the honda's used to have what ?? 16 speeds ?? and why ACU FIA whatever said ..

'Oi .... More than 6 gears .... Nooooooo !'

Gixergav wrote:

---

Not all race bikes run with open valves.The yamaha yzr 500 gp bike did indeed have a fully working ypvs system run off an isolated battery.If the battery ran flat however then no more ypvs.
Opening the valve and locking it off is more common on club racing bikes.Ideally you aren't ever below the powerband on the track.If you miss a gear though you just lost nine places!

---

YZR ?  Total Loss System Huh ??

a bit like the RD500 then .. !  [still love em mind, but would NEVER buy one !] .. Gp bike for the road ... my arse !

500 Suzook ?  Press bike fiddle ... Road motors struggled past 9k !
But Gp Bike for road ... Closer !?

Missed Cog = 9 Places .... 

xtopher66 wrote...

Simon, the other bottle is regarded as a restrictor and is advised to be blocked on the de-restriction page. Thanks for explaining the above on the newer bikes.

My era was just as restruction came in 1977 so tuning the new ones was first on the agenda! Believe it or not my 50cc was capable of 75mph tuned with flowed head, rotary inlet valve, gearing, chop the mudguards to lighten (everything was chrome back then) and expansion chamber. "its all about back pressure" the mechanics explained!
You would have loved the RD125 Twin esp with 2 Micron chambers on each port, and thats all they needed to hit 95mph......but yes the eurocrats and swiss want to tame us all.

Im not really sure about the technology of now, so thats why i ask. Ypvs werent around then!

---

-- Edited by SimsonS51E at 14:01, 2009-01-16