Thermostatic air cleaner isn't working
 

So the flap in the air cleaner that diverts hot air from the exhaust manifold into the carburetor has stopped closing, and as such it's pulling in cold outside air on a cold start. Just in time for winter of course. I checked the vacuum line to the carb it's okay, so I'm not sure what I need to do to fix it. It's on a '75 350 four barrel. I took some photos if it's any help:

Re: Thermostatic air cleaner isn't working
 

Since you have already tested the carb port, you have three things that can fail.
1. The hoses connecting it all. Replace them all, see if it works.
2. The vacuum pot on the flapper valve. Easy to test, just pull off the hose and hook a temp hose to a source of vacuum. The carb port you connect it to is good. If the pot is good, the flap should close. Perform this test while replacing the hoses.
3. The green thermostat. If everything else is good, this is your culprit. Note which hose goes where on this one, it makes a difference.

Not sure of new parts availability, especially the thermostat. I have had both the thermostat and vacuum pot fail, but at different times. Managed to find replacements for both at the local pull a part. Currently using a thermostat pulled from a mid-80s generic GM car. The style was different, (it was thinner), but the ports and spacing were the same.

Re: Thermostatic air cleaner isn't working
 

The correct vacuum switch for the mid-70s 350 is GM 6484244. That part number cross-references to an Echlin 2-2202. NAPA carries them
http://www.napaonline.com/Catalog/Re...Dp%3d3%26N%3d0

For a 75/76 V8, the GM part number for the vacuum motor is 6487370. For 77/78 350, the GM part number is 8994262. These are NOT easy to find. I found an old air cleaner at the junkyard. Sometimes they come up on ebay. You can also search at car-part.com. I found a bunch of compete air cleaners for 75-76 350s there.

Of course, you don't have to replace it if it's OK. You can test the vacuum motor by just hooking a line to it and sucking on it. You should be able to move the air door. If you can't, and when you suck on it, it leaks air, then it's dead.

Re: Thermostatic air cleaner isn't working
 

Thanks for the information guys. I'll have to do a few tests tonight.

Re: Thermostatic air cleaner isn't working
 

The vac. hose closest to the outside edge of the air cleaner actually goes to the flapper motor and the inside vac. hose closest to the opening that surrounds the carb. goes to the barb/tube which goes thru the choke linkage. I fixed mine by installing a new sensor, the green part in your picture, and watching with a mirror and headlamp the flapper closing at start up on a cold morning then opening when the temp reached its require degree. Part I bought eBay for $15.99 is : Buick Caddy Oldsmobile Pontiac Chevrolet air cleaner temperature sensor 6484244

Re: Thermostatic air cleaner isn't working
 

520CheyenneK10 if you know where to buy a GM 6484244 for $15 i will buy one.

Re: Thermostatic air cleaner isn't working
 

Just bought on Ebay last week.

Seller: Noschevparts

Ebay Item Description: Buick Caddy Oldsmobile Pontiac Chevrolet air cleaner temperature sensor 6484244

My Specs:

1973 K10
SBC 350
Auto Trans.
Quadrajet 4 barrel
Stock Air Cleaner and Vacuum hose configuration

Re: Thermostatic air cleaner isn't working
 

Wow you got lucky.

Ebay says that seller is not available till 11/12/24?

Re: Thermostatic air cleaner isn't working
 

Probably just out of office/town . I have seen this before . Just save it to your watch list and hit him up after the 12th.