Question about 76 Coupe Deville Charcoal Canister

[Aprules2]

I have a 75 Coupe Deville with a 76 Quadrajet on it. I spoke to the local carb rebuilder (Who happens to be a Caddy Guy) I am going to use and we discussed my options as far as the carb, and possibly getting a good 75 core. I told him my car's symptoms and as we were talking he asked if my charcoal canister was in good shape. I told him the previous owner had disconnected it. So today I went out to reconnect it and I hooked things up right I think... The 75 Charcoal canister has a connection for Purge, Vent, and Carb. I hooked the purge line up to the fitting in the base plate of the carb closest to the drivers side of the carb, the vent went to the hose from the tank vent. But in all the pictures the 75 carb has a vent on the top of the carb, my 76 carb doesn't have that so I just caped the line off at the canister. Does the 76 canister have only 2 connections on it?

[joeceretti]

I don't have any answers but am curious about your car's symptoms.

[Aprules2]

The car has a semi rough idle, dead spot in the carb when accelerating, and very poor MPG around 6... Also in the morning a little hard to start, and it wont do much of anything unless its warmed up. According to him there is pressure stored in the fuel system when you turn the car off and it sits the fuel actually pushes through the carb and ends up in the intake, causing fouled plugs, and creating my rough idle. The charcoal canister helps balance the pressure in the fuel system and at the same time helps recirculate the fuel vapor from the tank. He told me to try this before bringing in the carb to be rebuilt he said on his 78 he noticed a 1-2 mile per gallon increase with the canister connected vs. disconnected. With it reconnected my car does idle slightly better also my fuel filter used to be about half full at idle its now 99% full, it restarts better, but I havent had enough gas through it to see if its any better on gas.

[Joe G 12138]

You are right. 1975 has the only 3 connection canister that I'm aware of. 1976 uses a 2 connection charcoal canister. 1975 carb is an oddball too, with a fitting to go to the canister as well as some internal differences (altitude compensator?). You should be able to plug the extra fitting on the '75 canister and use the '76 carb.  But make sure the "76 carb has the vacuum port in the rear for the power brakes if you're using it on the '75. I've run into some '76 Carbs that were blanked off (NOT drilled and tapped) because of the change to hydraulic power brake boosters on the '76 Eldorado's.      Joe Gibeault

[Aprules2]

You're absolutely right the 75 Carb is an oddball, Im debating on getting another one. My car actually has a tap on the manifold for the power breaks, and another for the cruise and air cleaner. 

[R Schroeder]

My 78 has the 3 line hook up, where as the 77 didn't. Go figure. I'm surprised they kept changing it.

Brake vacuum is also out of my manifold.

Roy

If you want a 3 line hook up , there are 2 rebuilt carbs on Ebay. Both around 250.00.
Type in 17058230 Quadrajet. Number for the 78 carb.