Just took the 76 project car down to attempt to get smog first time. Thought I had all the emissions items included for the federal 76 vette, but didn't have the Evap Canister or hoses. Now I have the canister but can't seem to determine where all the ports are connected. Purchased the Evap hoses from Doc Rebuild with little instruction on how its connected to the carb. This is what I think I know:

1. Bottom of canister connected to metal fuel line in from gas tank
2. Port 1 on top of canister appears like it will be spliced in at the PCV valve then run to Carb.
3. Port 2 on top of canister says vent pipe hose in the build manual. WHERE DOES THIS LINE GO? TO THE CARB ALSO? CAN'T FIND THE PORT ON THE HOLLY CARB WHERE THIS NEEDS TO CONNECT.

Thanks

 

You do realize the car did not come with a Holley?
Look at diagram, seems like one of the top pipes is just described as vent and connects back to tank in second diagram on right
http://repairs.willcoxcorvette.com/1...an-hose-route/

 

Thanks for the response

Yes, Carb should be a Quadrajet which I'm told may actually perform better than the Holly I have now that came with the car when purchased. Visual test did not raise any issues with the Holly carb although just the evap canister as they need to do a pressure test now in CA.

Ok. so the it wold appear that there is a feed into the bottom of the canister from the tank and the 2nd port on top also connects back to the tank? I didn't see any additional ports so I'll get under there and see if its there for that port to connect back to the tank.

Thanks

 

The plastic tube on the bottom of the evaporator canister is just a drain pipe. It does not connect to anything.

 

According to the '76 AIM and how my car was initially setup the vapor canister is simply not connected to the carb. '76 have two connector a the top, one goes to the tank, and the other one is left unconnected. The bottom connector isn't a connector, just an overflow.
I personally switched to a vapor canister with 3 connector at the top (got it at the scrapyard from an 80's cadillac), one for the tank, one for the carb vaccum before the throttle body and the last one for the carb vaccum after the throttle body. This way the carb suck from the canister only when the throttle body opens, thus not disrupting the idling.

 

Did you look at the diagram in post #2 above? Isnt that straight out of the AIM?
It shows the bottom not connected.
The top with one hose going to tank and the other to port on carburetor.
Why would you have an unconnected port on the top?
Where do you think the gasoline vapors are going to go without a connection?

 

This makes more sense to me now. Thank you for the feedback. Here's the plan:

1. Connect the tank port to the metal line in from back of gas tank. Diameter seems to be consistent with both ports.
2. Connect the Carb port to a "T" at the PCV valve that connects to the ported carb.
3. Leave the bottom unconnected as overflow.

Got it! Best insight on this sight. Thank you. Its been 5 years working on this and hope to have it legal and on the road ASAP!
Cheers

 

Well, this diagram is not on the AIM I have, believe it or not.
Connected or not to the carb the vapors will again goes thru the charcoal of the canister, it's just that it would rely on the tank pressure rather than the vacuum.
I know it sounds weird, I've spend a while scratching my head over that.

 

For the vapors to even reach the canister there has to be something sucking them in, that is the connection to a vacuum port on the carburetor.

 

There should be 3 connections on the top of the canister. One is for the vent line from the tank. The other 2 nipples are the Purge Valve. Some models have a 4th nipple for connecting to the carb float bowl vent tube. There is also a vent port in the bottom of the canister to allow air to flow through the tank and dry out the charcoal during the purge operation. In order for the system to operate, the canister needs to be "purged" of fuel tank vapors by engine vacuum. This vacuum purge comes from the PCV line "T." However, if this line is exposed to manifold vacuum at all times, it will act as a giant vacuum leak at all times, completely screwing up your idle. So the Purge Valve controls when the canister is allowed to "leak" vacuum for the purge. This is triggered by ported vacuum being applied to that 3rd nipple on the purge valve: With no vacuum applied at idle (from the ported vacuum source), the purge valve stays closed - there is no vacuum leak through the PCV "T" to the canister. Once the car is up off idle and into cruise mode, ported vacuum is applied to the purge valve, and it opens up to allow a vapor purge of the can and the system. This ported vacuum is controlled through the manifold water temp vacuum switch located in the intake manifold water crossover just on the passenger side of the thermostat housing - this prevents operation of the EGR and the Purge Valve when the engine is cold (on fast idle).

The ported vacuum nipple on the stock Q-Jet is the nipple that also operates the EGR. There is a "T" in the EGR ported vacuum line that sends the signal to the Purge Valve. Your Holley should have a ported nipple on it that can be used to operate your Purge Valve. You must have all 3 of these lines correctly hooked up to the proper vacuum sources in order for the system to work.

Lars

 

Nice explanation Lars. On the canister that I have for the 76 there are only two ports on on top and one on the bottom. First top port says carb and second says tank. The bottom port appears to be the vent port you mention to purge. Last night I connected the carb port through a "T" at the PCV valve which is connected to vacuum on the Holly Carb. The Tank port was then connected to the metal line in from tank. Are you suggesting that I shouldn't be connecting to the PCV valve with a T, but only to a separate vacuum port on the carb. Without a 3rd purge valve on the canister or another vacuum port on the Holly carb I'm not sure where the canister port should go. I'll start it up once back on the ground and see how the idle and to what effect the current configuration has on the idle.

Thanks for all the insight!! One last step to get this vette legal.......

 

I think (and Lars can confirm ) on a 76 a q jet has a hose port on the front up high I assume goes to the fuel bowl above the gas level vapors are vented internally from there. I also have a 76 without the original q jet. My canisters plugged also.

 

The Q-Jets with the bowl vent nipple were used only on certain years. This vent nipple is attached to a dedicated port on the canister for the appropriate year. It can also be effectively "T'ed" into the vapor vent line from the tank.

Carb with bowl vent:


Carb without bowl vent - carbs are otherwise almost identical:


Lars

 

Do any of you have or know where I can find a hose diagram diagram for the carb with a bowl vent or maybe some pictures my hoses are all over the place