What is the window in piston for?

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Feb 2, 2001
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#1
My 97 RM250 has a nickle size hole in the intake side of the piston....the window. Is this the cranks only source to pull in fuel? Or does fuel draw in from under the skirt as well? Just curious, because I ran my piston backwards and am wondering just how little premix was getting to the crank.

Micah
 

CaptainObvious

Formally known as RV6Junkie
Damn Yankees
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Jan 8, 2000
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#2
Off the top of my head, I think the window is to get lube the piston pin bearing. I think the charge is drawn in when the port is exposed on the up stroke.
 

Jman271

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Oct 18, 2001
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#3
Normally it is to lengthen intake area during the stroke,,,,are you talking about the window directly under the ring, @ reed side? If so, that pretty much sums it up I guess. It will see some lube, but the idea I think was for intake area,,,,