EGR

[bruce plecan]

OK, any commonly in use 4 cycle engine has some EGR built into it.  The
only exception to this is one Buick turbo cam, that I know of.  The
reason for this EGR is that for a moment both the in+exhaust valves are
both open.  There are times when this effect is very small, but for the
first instant before the intake air begins to move, exhuast gas rises
above the intake valve head.  Ever notice on some engines there is so
much gloop on the back side of the intake valve,  yes some of that is
due to the valve guide seal not being perfect, and the actual heat of 
the valve, and the fuel laying above the valve head after it closes but
some of the heating, and carbon is from this nature EGR effect, IMHO.
     EGR valves, there are two types.  One uses vacuum only to open it,
and the second is a back-pressure egr valve.  The term backpressure EGR
means that reguardless of the vacuum applied to it, exhaust backpressure
can open it.  So the absolute rule of the EGR valve not opening at WOT
ain't always so.  If you want to know if yours is opening, built a little
jig, using piano wire, to touch the steel reinforcement of the diapham,
and wire it to power, a LED, and 1K resistor.  Then go out and stand on 
it depending on how you have it wired the light will go on or off as the
valve lifts off the seat.  The only way to make sure the EGR doesn't open 
on your off-road vehicle is blocking the port.