As title says i,ve noticed that when the power valve is at rest its flush in the exhuast port but when its in the open position its actually closing in the exhuast port is this a restriction if so how do you sort it thanks
Before you start doing anything, open the cover on the side of the cylinder and start the engine. When its ticking over, you'll see it moves to the more restrictive position - now rev it high (7K+) and you'll notice it moves to the less restrictive open position. When you kill the engine it moves to the less restrictive open position.
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Just because I don't care, it doesn't mean I don't understand...!
upside down then haha, disconnect the cables, pull pulley out, twist the powervalve 180 degrees, put all back together and align the pulley to the hole and rrrrraaaaaaaaggggggg
well i looked up my exaust port after cleanin stroke n my pv was abt 2mm proud ,so set it flush wiv port n lost power ,, set it up as per manual align hole etc n was faster !!but pv sticks into port slightly??? if i set my pv so hole in plastic pulley is set to the left of the hole in rear casingn has greatly improved acceleration ,ask craig bulmer on ere hes tried it n says it does improve acc !! DAVE
well i looked up my exaust port after cleanin stroke n my pv was abt 2mm proud ,so set it flush wiv port n lost power ,, set it up as per manual align hole etc n was faster !!but pv sticks into port slightly??? if i set my pv so hole in plastic pulley is set to the left of the hole in rear casingn has greatly improved acceleration ,ask craig bulmer on ere hes tried it n says it does improve acc !! DAVE
Its not about being flush with the exhaust port, its all about when the port opens on the piston downstroke. The only way to properly set it up, i.e. as Yamaha designed, is to do it as per haynes or the proper Yamaha service manual - using the 4mm pin method. Adjusting it clockwise or counterclockwise will only move the power up or down the rev range, with better or worse power delivery accordingly. It WON't give you any more power.
Set it as designed, and leave it. It's for the best overall performance.
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Just because I don't care, it doesn't mean I don't understand...!
That's interesting malc. When I set the PV flush on mine I noticed the pulley did not align with the hole and was slightly offset. So this would actually be correct?
That's interesting malc. When I set the PV flush on mine I noticed the pulley did not align with the hole and was slightly offset. So this would actually be correct?
Yes, if you set the powervalve flush with the exhaust port roof, it won't align at the pulley.
Not sure if you're aware, but the power valve doesn't work on being flush or otherwise with the roof of the exhaust port, but rather the opening time of the exhaust port against piston travel on the downstroke. Its difficult to explain in words, but when at low revs, the PV barrel rotates so the top of the exhaust port is level with the piston crown further down its stroke, as the revs increase, the PV rotates to in effect raise the top of the exhaust port hole, so the piston crown is level earlier. I wish I could find a drawing I did earlier cos it explains so much better than words ever could.
As a PS, Suzuki do it different on the RGV, etc. in that they use a blade which moves up and down but has the same end-result. Not sure how Honda and Kawasaki do theirs, but I'd bet its one or the other method...
Edit - found, third post on page 2... http://www.activeboard.com/forum.spark?aBID=66365&p=3&topicID=34662185&page=2&sort=oldestFirst
Check also here on Wikipedia, gives a good overall description of the Jap 4 power valve systems... http://en.wikipedia.org/wiki/Two-stroke_power_valve_system
-- Edited by Malc on Saturday 24th of July 2010 07:46:39 PM
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Just because I don't care, it doesn't mean I don't understand...!
I never knew that, learnt something new there. I understand your picture.
Ok so when the pv rotates to raise (open) the top of the exhaust port hole, on the down stroke the piston crown is level earlier improving power delivery in the higher revs and vice versa.
Is it something to do with the pressure and exhaust gases. So what the PV is doing is changing the size of the exhaust port to match the amount of exhaust gases released at different points in the rev range.
So by me or anyone making the PV flush to begin with, this will actally decrease performance in the lower revs and acceleration will be affected...which is what hairdoo noticed.
Am I understanding this right haha? Thanks for explaining.
Basically, your powerband (NOT a part but where your engine makes all its power in its rev range usually 7-9k rpm) generates more power in this rev range than the low rev range etc... The power valve system in a simplified way is as follows..
It shifts your powerband up and down the rev range in response to your revs.. For e.g you rev at 4500rpm your powervalve with it movin the exhaust port earlier in line with the piston gives you better performance at all rpm.. So the power valve of course just moves your powerband (in a way) up and down your rpm, so no more 2t boggin on the low rpm :)
Sorry im new to all this but i thought if i practically understand how it works i could put it in more simple terms for the people whos sat reading this scratching their head lol ;)
