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2 Stroke Power Valves Pointless?

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Do I recently bought my first 2 stroke yz125 and it was modified for a racing kart. One of the items that was modified was the power valves were disconnected and pinned wide open. So I guess I'm wondering why even put power valves in an engine anyway, wouldn't it perform better through the entire Rpm range without them? Is there a reason for the additional back pressure during lower rpm?

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Yes they have a purpose. If you disconnect them wide open, you won't have a whole lot of response and torque on the bottom end of the RPM range. Kart engines are meant to be in the powerband pretty much the entirety of their usable life. You don't lug a kart, but a dirtbike you DO lug so it's generally a good idea to have powervalves.

They wouldn't have invented them if they served no purpose ;)

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Simple explanation: lower port height =better low end power, heigher port height=better top end. Before powervalves, power was more of a compromise.

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Karts go 'round and 'round on the same track, and unless the driver mis-counts a shift or has to panic brake outside a normal braking zone, there is no reason for it ever to fall out of the peak rpm powerband with a competent driver.  If there was such a thing as a 2 stroke "trail kart" or "MX kart", it would have a power valve. 

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When the valve is open the exhaust pressure pulse comes back sooner. At low rpm much too soon.

Search YouTube for how a 2 stroke pipe works.

A power valve makes the power band much wider.

The only reasons to not have one is if
1. You don't need a broader power band. Eg. Road racing. Or a large displacement motor.
2. you cannot fix it within your budget for new parts.
3. You prefer not to have the extra mechanical parts. Want a simple motor.

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