‘72 Mark tank venting

[TonyC]

Well, if it is in fact blocked, then try putting in the new one. It isn't something you're going to be thinking about with normal driving, but it will be insurance against too much pressure building in the tank, which can either throw fuel onto you when you remove the cap, or in a worst-case scenario compromise the seams of the tank and cause it to leak fuel. As I surmised, the tube is tiny for a reason: To bleed off air pressure without bleeding off liquid fuel.

If, when you remove the cap to fill up, you notice that inside pressure is less than it used to be, then you know the new separator is working.

---Tony

[1Bad55Chevy]

So as described above, the line is open but the vent separator is blocked. I don’t need any shop to verify this. The issue is whether that makes any difference given how small the hole is in the separator. I’ve NEVER heard of this causing a problem in any car. Yea, I’m throwing parts at this, there is no doubt the separator is blocked.

Really?

I deal with the refueling issues about every month or so at the car lot. I get these cars all fixed up just to find out they need the EVAP systems rebuilt when I take it to put gas in them. I wonder if you could wash the charcoal canister out since I do that to the late model GM trucks when they have issues. You would really be surprised if you saw how much junk comes out of one of those.

[Goldstar]

Thanks for the help, boys. I’m going to try one more thing before dropping the tank and installing the vapor separator and that’s replace the cap and see if that makes a difference in vacuum. My cap seems to be good as I can suck air out the valve but who knows…and they’re cheap.
Again, my charcoal canister is not a problem as I can blow air through it very easily, same as the vapor line. I can’t blow or suck air into or out of the separator, sp I know that’s where the blockage is. I’ll keep you posted

[Goldstar]

After examining the vapor separator, I now believe my tank is venting properly and the blocked separator is not causing either the engine stumble or related to fuel pump nozzles cutting off when fueling. The stumble was caused by the carb flooding (now resolved), and fueling difficulties are due to having to turn the nozzle sideways to get it to fully engage in the tank tube behind the license plate. The vacuum swoosh I hear when opening the gas cap I think is normal. I got a new cap that vents and it does the same thing. Anyway, the car now runs great, thanks for all the help and support.