I am finishing up my new 406 build installation in my 77, and have following questions. Installed Holley 4150 Street HP 750 Aluminum carb on Edelbrock RPM Air Gap.

- Factory 77 fuel vent / charcoal canister has a hose from the canister to the carb to provide vacuum to the gas tank. Quadrajet had hose fitting for this; this Holley does not. My research shows that some T this into the PCV hose between the PCV and carb fitting. I would prefer not doing this, as I have the Wagner adjustable PCV valve, and would like it to go to the base of the carb without the T. On the Wagner FAQ page, it recommends to run the hose from PCV valve direct without any T fittings. So, can I run the canister hose to the larger rear port on the 4150 that is typically used for power brakes (my car has been converted to manual brakes)? When you look at base of carb, It seems to me that its pulling from the same vacuum as the PCV port....the area under the throttle plate. Just FYI, on a 77 charcoal canister, there is no ported vacuum to operate the non-existent switch on the canister.....just one line in from the tank and one line to the carb for vacuum. Earlier C3 used a ported vacuum to control a valve on the charcoal canister......77 does not.

- I bought one of the large billet adjustable throttle cable brackets with the two return springs on the front side, and adjustable block on rear.....but even in the lightest spring position, it requires alot of force on the pedal to move the throttle....very stiff. Holley makes the 20-88 bracket for this installation, bolts to the rear left corner, with double springs, much like the Quadrajet setup, but I have read it does not fit well and is too flimsy. Is it really? Summit reviews show several people very happy with this bracket. I am tempted to try it, but looking for anyone here who has used it. I just don't like the amount of pedal force it takes to hold throttle open with this billet setup. Given the amount of driving I do (a lot), think it would get annoying. Its definitely way more force than the Quadrajet took.

 

Vacuum is vacuum......yes you can run it to that port.
The bracket is kinda cheesy....but I have used it with success with a stud kit....not bolts....it has to be tight. I put stainless ARP on everything now becasue if you don't....it will look like **** in two years.....even my float bowl screws are ARP and the sight level is Holley Stainless.....pricey, but I bought one kit at a time.....and didn't drink beer that week....LOL!

Jebby

 

Thanks Jebby. These vacuum fuel vapor canisters have been changed alot over the C3 years. Pre-74 they had a purge valve that did not open the vent line till after idle. It was controlled by a the timed vacuum port on the carb. Then 74-77 seems they eliminated the purge valve, and the big hose goes to a large fitting (lower front) on the Quadrajet that appears to me to be channeled ABOVE the throttle plate. I just want to be sure that pulling full manifold vacuum ALL THE TIME on the vacuum canister will be okay and will not effect idle quality. Seems like its a "vacuum leak" at idle......to me. But maybe I am overthinking this.

 

I misunderstood and thought you meant the brake booster can.....
Yeah, that would probably leak all the time.
I would unhook it and put a cheap filter at the end of the hose that goes to the tank.....that is what I did....
I left the can in for now but will end up removing it as it blocks the vent a bit.....
The only vacuum I have on my 406 is Advance Can, Brake Booster, PCV, and main Vacuum Cannister....
PCV, Brake and Vacuum Resevoir are all separate too....the original had the PCV tied in with the Evap can I believe....PCV had a tee on it....

Jebby