Power valve

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Jun 8, 2001
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#1
Hi there.

I'll like to know how does the power valve works in the combustion process. I only know that in high RPMs, the valve "opens" up to allow more exhaust out but do not understand how it works in relation to the exhaust port.

I notice that on my DT200WR, on the left side of the engine block, there's a "cam" with two cables attached to it.
How can I fine-tune the bike using it?
 

RM_guy

Scared of DirtWeek<BR>Club *********
Damn Yankees
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Nov 21, 2000
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#2
The power valve does more than just allow more exhaust to escape. More importantly it changes the height of the exhaust port.

At low RPMs the top of the exhaust port needs to be low in order for the motor to develop better low end power. At high RPMs the top of the port needs to be higher for the motor to develop better top end power.

The power valve is used to change the height of the exhaust port and different RPMs by way of a governor (driven by the crank, or a servo motor as in the ’02 Honda) and a linkage. As RPMs build, the linkage opens the valve. Spring tension on the valve controls at which RPM the valve actually opens. You typically want to stay with the stock tension setting but it can be played with to control when the “powerband” kicks in.

The PV can also open and close additional exhaust ports depending on the design.

I’m not familiar with the “cam and cables” on your Yamaha.

Good luck
 

smb_racing

Master of None
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#3
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#4
Thanks guys for the information

Now I have a pretty rough idea how they work in relation to the engine.