Need help Identifying a 620 part

[650savag]

I will post a picture when it is light tommorow but I'll bet some of you will know what it is when I describe it. I need to know what it is and what function it is suppose to have? It's a small switch like apparatus that is mounted on the firewall on my '78, 620. It sits to the left of the brake booster and has a small vacuum hose connected to the vacuum line from the intake to the brake booster. It connects to a small pigtail "y" in the booster line. It has another small vaccum hose that runs the other direction down the firewall, toward the passenger side, but the hose has deteriated, and is just hanging loose, not connected to anything. It also has one wire that plugs into it that comes out of a harness over on the passenger side fender well. So do I have any takers on this "Pop Quiz" before I post a pic tommorow? Lets have a race to see who can guess what it is first! Thanks for everyone's help as always! Dan (650savag).

[datzenmike]

The loose hose may connect to the anti back fire valve located just behind the carb. It has two thumb sized hoses, one from the air filter and one to the intake, and a small hose connected to vacuum. Three in all.

 

Yours obviously has an electric switch to control when it is working or not, like when the clutch is in or if in neutral. My '78 does not have this switch and is connected directly to manifold vacuum at the hose to the brake booster.

 

It's function is to prevent overly rich mixtures caused by high vacuum levels on sudden deceleration. A rich mixture would ignite in the exhaust and back fire, damaging the air pump. The anti back fire valve admits extra air into the intake to reduce the high vacuum levels.

[650savag]

Mike, Thanks for the great info on that mystery switch. That makes me feel a little easier. I was concerned that it may be a source for a vacuum leak. My truck is completely de-smogged. I have removed the EGR valve and installed a block plate and blocked all asssociated vacuum lines. I have also removed that anti-backfire valve and plugged all it's hoses. When I did the manifold gasket job recently, I removed the EGR tube and plugged both ports (exhaust and intake). The only hose that is hooked to the intake now is the crankcase vent hose with the PCV valve. The only hose that is hooked up to the stock Hitachi air filter breather is the vent hose from the top of the valve cover. I haven't had any problems with performance or backfiring and I can change out the Hitachi in about 30 minutes (lots of practice) Ha! Mike or some of you other guys here that are really tech savy, please help me out and tell me if I'm asking for problems with all the de-smogging that I have done. Thanks, Dan

[datzenmike]

It was a guess by process of elimination. Could be something else. Cars ran without much pollution stuff for years yours should too. The only long range problem is if you are subject to smog inspections or choose to sell. It would be best to hang onto all the old parts.

 

What did I win??????????:lol:

[650savag]

It was a guess by process of elimination. Could be something else. Cars ran without much pollution stuff for years yours should too. The only long range problem is if you are subject to smog inspections or choose to sell. It would be best to hang onto all the old parts.

 

What did I win??????????:lol:

 

Hey Mike, Thanks for the help on this item! I don't plan to sell "Ole Blue" but I might sell my '80 model 720 one of these days. It's my backup work truck when I'm working on the '78. You gotta be kidding about the pollution/smog inspections in Louisiana! You ever drive around down here? Ha! Anyway, I'll keep all the parts just in case. You won the race by default, I guess, cause nobody else has responded yet. Your prize is knowing you are a "good guy" for helping out an old "coon ass" grandpa! Thanks again, Dan