reredol

got a 80 L48 auto, on the top of the thermostat housing are 2 thermal vacuum switches, one brown for the EFE and one black, connected to the the distributor and to the carburator.

This switch is broken. What does this switch do?
when I connect the hose directly from the distributor to the carb, I got a smooth idle (700rpm) and the engine is easy to start, when it's warm. When I interrupt the vacuum line, the idle is rough (500rpm), and the engine is hard to start, almost stall when it's warm and I swtich to "drive".
It's hard to find a black TVS, all the corvette parts dealer only have the EFE and the EGR TVS.

What schould I do?

Thanks George

In the vaccum diagramms of serveral books are many varieties of the vacuum rootings, one with the black TVS, one with out. On the hood of my corvette is a emission sticker, showing "CY" in the left upper corner.

Paul Borowski

I think this is what controls the vacuum to your EFE heat riser pod and possibly your EGR & or distributor vacuum. The switch is heat activated. When very warm or hot water hits it, it'll either "turn on" or "turn off" when activated. You may need to go to a dealer or an AC Delco parts jobber or locater to find one. This type of part was used on many GM cars of this era, so you should be able to get one.

page62

Yeah, but it might be a little more challenging for him to find one in Austria! :banghead:

Paul L

See top-right diagram. The set-up with two TVSs on the t-stat housing is pretty rare. I have only seen it once and that was on a 1979 intake that I rebuilt. It seems that he has the more typical EFE switch in place on the housing and the EGR switch on the intake but has broken the second switch on the housing. BTW I just replaced my housing with an EFE/one-hole type.

Looking at the diagram, and seeing vacuum advance running through the broken switch, it is my guess that it represents a thermal block on ignition vacuum advance until warm-up (typically a coolant temp of 120-180F). But I do not know why the system was designed that way and why it found limited application!!

The odd thing about that switch is that it does not appear in the various Corvette catalogues, including the usually reliable Dr. Rebuild. And I would guess that a GM parts person might have difficulty in finding it as well.

My inclination would be to forget about it and go with a new single-hole/EFE T-stat housing. The poster may have to re-route some of the vacuum hoses as per the other diagrams but I am confident that the car will run well.

MILO

ZIP Products had the two pole switch for the EFE that goes into the thermo housing. Bought one about a year ago for my '79.

Paul L

I believe that he has the EFE TVS. You can see the indentation on the t-stat housing on this intake where some housings have an additional threaded hole for a second (un-named) TVS.