MONTE CARLO Need info on vacuum switches

Bludacious

Not-quite-so-new-guy
Jan 2, 2018
35
1
8
#1
I've recently converted my 305 from an electric to vacuum advance distributor setup. However, the 2-port thermal vacuum switch that was already on the manifold had a bad vacuum leak. Ordered in a replacement from O'reilleys only to find out it was open cold instead of hot and also broke into pieces while I was installing it. What I need to know is what the color codes mean for the switches and what part number I need to order to replace it. In addition, what is the purpose of the 'Ignition ported' switches with the small hole in the base VS the standard kind that don't have this hole, and which one do I need? Is the hole to give the engine more air during an overheat condition? I have no other engine to reference or get parts off of to determine which switch I need and don't want to return anything if I order from an online seller and get the wrong part. The original switch has this 'ignition port' and all emissions equipment has been removed from the engine.
 

Ribbedroof

Royal Smart Person
Jan 4, 2009
2,032
645
113
Wellston, OK
#2
IMO, if you have deleted all emissions equipment, and gone to a non-CCC distributor (and carb, presumably), there really shouldn't be a need for any of the thermostatic vacuum switches. They were used to ensure a very narrow set of operating conditions were maintained.

Essentially, you now have a pre-emissions engine. I would use an early 70s tuneup profile for a baseline and adjust timing and idle settings to achieve an acceptable mix of idle speed and performance.
 

Bludacious

Not-quite-so-new-guy
Jan 2, 2018
35
1
8
#3
IMO, if you have deleted all emissions equipment, and gone to a non-CCC distributor (and carb, presumably), there really shouldn't be a need for any of the thermostatic vacuum switches. They were used to ensure a very narrow set of operating conditions were maintained.

Essentially, you now have a pre-emissions engine. I would use an early 70s tuneup profile for a baseline and adjust timing and idle settings to achieve an acceptable mix of idle speed and performance.
I've adjusted the timing, but I need the switch to shut off the vacuum advance to the distributor when it is cold as it causes a rich condition making it very hard to start. Usually in the morning I have to crank it 2-3 times before it will turn over and not immediately die, at which point I have to keep my foot pressed lightly on the gas for a few seconds until it begins to heat up and can run without my assistance. This is fine for the summer weather, but I doubt I'll be so lucky trying to do this when it's below 40 outside
 

Ribbedroof

Royal Smart Person
Jan 4, 2009
2,032
645
113
Wellston, OK
#4
Sounds like the choke is not operating correctly. Have you checked to see if it is operating?
 

pontiacgp

Canadian Prime Minister
Mar 31, 2006
22,590
3,576
113
Kitchener, Ontario
#5
x2 on the choke being the issue. If you plan to do your own work on the carb I suggest you pick up a book on the car, Doug Roe and Cliff Ruggles each have a good book on a quadrajet.
 

Bludacious

Not-quite-so-new-guy
Jan 2, 2018
35
1
8
#8
I would suspect the choke as it did need to be adjusted when I swapped it onto my current carb, but it never had any issues cold starting before I changed the distributor with the choke at its current setting. It also never gave me any issue on the original carb, it only started having issues when I connected the vacuum advance directly to the carb and not the ported switch.
 

Bludacious

Not-quite-so-new-guy
Jan 2, 2018
35
1
8
#10
Perhaps I may have worded my initial post incorrectly. My issue is not with a constant rich condition, but when I do cold starts I can smell a lot of unburned gas out the exhaust. Since I now have the vacuum advance connected directly it over advances the timing causing it to start hard and it stays down on power until it warms up for a few. The feeling actually does seem very much like a choke issue (dies if you rev it before it warms up, hard starting) but I know the choke is opening and it never had this problem before I bypassed the switch. Once it is up to temp it runs fantastic, I don't want to retard it any because it seems fine where it is when the engine is warm (no pinging backfiring etc). I know it operated correctly with the advance routed through the switch because despite the leak it started easily cold and ran fine, though the loss of vacuum was definitely noticeable.
 

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