what does disconecting the power valve do

D

deadwaterj

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Sep 14, 2002

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• Sep 14, 2002

• #1

ok, some one wrote that if u disconect the powervalve externaly on a kx 250 it rides like a kdx 250, please explain this to me.



:aj:

 

G

grass-digger

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Oct 21, 2001

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• Sep 15, 2002

• #2

it would probly loose your top end power or loose your bottem end power

 

RM_guy

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• Sep 15, 2002

• #3

You will loose your top end power. Low end will be the same as it was before disconnecting it.

 

S

Stew312

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Jul 8, 2002

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• Sep 16, 2002

• #4

The valve will not be able to close & restrict backflow from the exhaust pipe under higher rpm's, which will greatly reduce your top-end power.

 

Rich Rohrich

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• Sep 16, 2002

• #5

If you disconnect the power valve you have a very high risk of overheating the piston crown and/or running into a serious detonation issue. There will be too much cylinder pressure for high rpm, high load situations. This isn't a good idea.

 

Last edited: Sep 16, 2002

RM_guy

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• #6

Originally posted by Stew312
The valve will not be able to close & restrict backflow from the exhaust pipe under higher rpm's, which will greatly reduce your top-end power.

Click to expand...

:think: Ya got that backwards. The PV opens at high RPMs to raise the exhaust port and to allow for better exhaust flow out the port.

BTW, Is anyone actually planning on disconnecting the PV? Why?

 

S

Stew312

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Jul 8, 2002

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• Sep 16, 2002

• #7

Are you positive? When was the last time you tore down the engine on your RM?? Notice how when you set the left side pre-load spring you turn it counter-clockwise? That puts pressure on the valves to open, which causes them to stay that way unless acted upon by the actuator arm, which closes them under higher RPM's. Unless my brain just died on me, I'm pretty sure thats the way it works.

 

S

Stew312

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Jul 8, 2002

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• Sep 16, 2002

• #8

(by close I mean being pushed downward reducing port volume)

 

S

Stew312

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• Sep 16, 2002

• #9

wait, maybe I'm thinking backwards...

my brain hurts.

 

B

bigred455

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• Sep 16, 2002

• #10

When the motor hits a certain rpm the governor arm(kx anyway) pulls the whole rack open, including the exhaust flap which would go up or open position.

 

RM_guy

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• Sep 16, 2002

• #11

Originally posted by Stew312
wait, maybe I'm thinking backwards...

my brain hurts.

Click to expand...

That will happen when you try to think backwards :eek:

I figured if I just let you ramble on you'd get it right :)

 

S

Stew312

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Jul 8, 2002

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• Sep 16, 2002

• #12

haha, I think I better go home and check my pre-load spring! :eek:

 

S

Stew312

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• Sep 16, 2002

• #13

Well to continue my rambling, I just realized that my hard starting (have to lie the bike on its side so it floods, even after its been running!!), terrible idle, plug fouling, etc may be due to the fact that I pre-loaded my exhaust valves to stick open, cause by me reading dissasembly of preload spring during my assembly resulting in a counter-clockwise turn, instead of the appropriate clockwise turn. Looks like someone has some work to do before this weekend. Can we say, ooooppssss. :scream:

 

MX-727

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• Sep 16, 2002

• #14

Good thing someone was thinking about disabling their PV. :)

 

S

Stew312

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• Sep 16, 2002

• #15

Yeah, seriously.. Well now let me say from experience, having a disabled PV is NOT the way to go!!

 

oldguy

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• Sep 16, 2002

• #16

definately not the way to go:( This weekend we took the kids CR125 up to Eric G for some tinkering. After doing the topend and some head work he noticed the power valve wasn't closed. Turned out during a clutch rerbuild last spring the mechanic didn't retime the PV and it didn't close up. Thekid was new to a 125 from his YZ85 and really didn't realize the bike lacked lowend. As the season progressed we went to Eric to get more bottom thus the discovery. Thekid couldn't believe the pull his bike has now. Figure the PV now works, a fresh topend, and Eric Gorr's magic :) the bike never stops pulling.

 

MikeT

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• Sep 17, 2002

• #17

"what does disconecting the power valve do?"


Ask Gomer.

 

RM_guy

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• Sep 17, 2002

• #18

Hey Gomer! What does diconnecting the PV do ???:p (Mikey told me to ask :debil:)

 

S

Stew312

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Jul 8, 2002

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• Sep 17, 2002

• #19

hey old guy, the bike act wierd in any other way with no PV other than no low end (fouling plugs, hard starting, etc)??

 

J

James

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• #20

Originally posted by MikeT
"what does disconecting the power valve do?"
Ask Gomer.

Click to expand...

I think he only knows what happens when you put it in upside down.

 

oldguy

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• Sep 17, 2002

• #21

Stew there were no obvious problems other then the lack of low end. I think he would have noticed if he had more time on it before the work that disconnected it.

 

MikeT

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• Sep 18, 2002

• #22

Originally posted by James


I think he only knows what happens when you put it in upside down.

Click to expand...

:) :)

 

R

RJH

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Jun 15, 2002

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• Sep 19, 2002

• #23

With the valve fully open (up) top end will stay the same - you will notice some mid range loss. In shifter karts, the valve is to be locked open. We have had no abnormal engine problems. The YZ125 revs easy to 13700 with a shifter pipe and makes HP up to 12250. As does the Honda and others. Bob Hogg

 

RM_guy

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• Sep 20, 2002

• #24

Shifter carts are alway in the top end so PVs are somewhat useless. That's whay they run them opened. Dirtbikes need a much broader power range and the PV gives it that.