Vaccume Operated Exhaust Restrictor Help!

[FlatBlack77]

ok so im going over a few things on my 79 K10 after driving it quite a bit and making a small list of little things than need attention.

the only one i have a question about is the stock exhaust manifold restrictor  valve. that little plate that uses vacuum that opens or closes im guessing to help with warm ups? on the passenger side exhaust manifold.



1 - it does it not have a vacuum line on it(so it is not working obviously)
2 - i have no idea which port on the carb it gets hooked up to
3 - i have no idea which position is open and which is closed

obviously with vaccume it will move(well maybe! its very stiff from not moving in who knows how long) but i dont know if it needs ported vacume or what and i surely dont know which position is open and which is closed

i have a working choke so I really dont need it unless you guys would recommend hooking it up properly. id really rather wire it so its open all the time.

"sucked in" position (pulling on rod)


pushing on rod (as if no vaccume to suck rod up)



again pulling on rod


and pushing


which is open and which is closed?

i dont have dual exhaust that would help figuring it out and i dont want to take the downpipe off its pretty rusty

sorry to make a long post and thanks in advance

[bd]

It's called an EFE valve (Early Fuel Evaporation) and is a glorified heat riser.  The valve closes to force hot exhaust gas through a broad passage integrated into the floor of the intake manifold.  While the valve is closed exhaust flow is temporarily routed through a port in the right head, under the intake, then through a port in the left head and out the left side exhaust manifold.  The idea is to heat the intake manifold just enough to keep fuel atomized and suspended in the intake airflow and prevent fuel puddling.  It improves cold weather drivability.  As the engine heats to operating temperature the EFE valve opens, providing unrestricted exhaust flow out of the right manifold.

From memory, the EFE actuator (the vacuum can in your image) has an internal spring that defaults the EFE valve open with no vacuum applied; the actuator pushes the valve open.  EFE is controlled by a thermal vacuum switch (TVS) threaded into the thermostat housing.  Manifold vacuum is supplied to the EFE actuator via the TVS while the engine is cold pulling the valve closed.  So, COLD: pulled closed by vacuum - HOT: pushed open by a spring (the default position).

As to their desirability, if heat risers were of no benefit, the OEM would never have installed them, saving significant expense.  EFE was a refinement of the heat riser to provide more precise control of valve opening in response to economy and emissions concerns.  Heat risers were the forerunners of thermostatic air cleaners (TAC).  If you reside in a cold climate and have TAC, but have no problems with carburetor icing or cold drivability symptoms, you should be able to dispense with EFE.  Unfortunately, physically removing EFE from the vehicle will present a new problem of mating the exhaust pipe to the right side manifold, because of the thickness of the EFE valve casting.  Of course, you could just leave it there and not connect vacuum to the can.

Edited for clarity.

[FlatBlack77]

ahh i see said the blind man. thanks for the info i never knew it worked like that.

unfortunately there is no spring and it doesnt stay one way or the other. i have to force it into either position and it will stay that way till i move it the other way

[zieg85]

FWIW, if they rattle it is usually associated with an exhaust leak at which time I gut the valve, weld up the holes and install it back with need gasket and donut gaskets.  I've never had an issue in the Chicagoland climate but I let my carb'd vehicles warm up before I head out.