Carbureted 350 vacuum line rebuild

[hatzie]

If it's a manual transmission with California emissions it's possible it originally had Transmission Controlled Spark Advance in 1970. That would explain the thermo vacuum valve in the thermostat neck.

You do want the PCV valve running to manifold vacuum and the PCV intake running to a filter in the air cleaner or a filter cap in the valve cover opposite the PCV valve. This will keep the crankcase seals from weeping motor oil.

The 1967-72 trucks had the fuel tank mounted with you behind the driver seat inside the cab. You have to put some kind of hose arrangement on the tank vent to carry the raw fuel vapor out of the cab.
Vented fuel caps aren't an option. The filler is right next to the drivers side door.
Three hose EVAP cans like the 70's F-bodies and Vettes used are simple and easy to install. They have zero negative effect on performance and they'll keep the garage or barn from smelling like raw fuel. They have ported vacuum to the purge control valve, fuel vent from the tank, and purge teed into the PCV valve hose for manifold vacuum to suck out the trapped fuel vapor. In short the charcoal EVAP can is a good thing.
If it's parked outside you could just run an SAE J30R7 fuel vapor hose from the vapor connection on the fuel sender to an axle vent. You'll occasionally smell raw fuel using this setup.
The other simple venting option would be to do what Nissan did with the Datsun 210... put an axle vent inside the air cleaner filter ring and run the tank vent hose up to that.

[57taskforce]

Originally Posted by hatzie

If it's a manual transmission with California emissions it's possible it originally had Transmission Controlled Spark Advance in 1970. That would explain the thermo vacuum valve in the thermostat neck.

You do want the PCV valve running to manifold vacuum and the PCV intake running to a filter in the air cleaner or a filter cap in the valve cover opposite the PCV valve. This will keep the crankcase seals from weeping motor oil.

The 1967-72 trucks had the fuel tank mounted with you behind the driver seat inside the cab. You have to put some kind of hose arrangement on the tank vent to carry the raw fuel vapor out of the cab.
Vented fuel caps aren't an option. The filler is right next to the drivers side door.
Three hose EVAP cans like the 70's F-bodies and Vettes used are simple and easy to install. They have zero negative effect on performance and they'll keep the garage or barn from smelling like raw fuel. They have ported vacuum to the purge control valve, fuel vent from the tank, and purge teed into the PCV valve hose for manifold vacuum to suck out the trapped fuel vapor. In short the charcoal EVAP can is a good thing.
If it's parked outside you could just run an SAE J30R7 fuel vapor hose from the vapor connection on the fuel sender to an axle vent. You'll occasionally smell raw fuel using this setup.
The other simple venting option would be to do what Nissan did with the Datsun 210... put an axle vent inside the air cleaner filter ring and run the tank vent hose up to that.

Not all 67-72 trucks have the tank vent. Tons of them came from the factory with a single feed line from the tank to the carb and that’s it. In which case they came oe with vented caps. Non vented caps came with the charcoal canister setup. I believe 71-72 at least maybe even 70 as well 1/2 tons had the eec canister setup but it wasn’t added to most 3/4-1tons. If the rubber line coming off the sending unit to the hard line is in good condition and the tank filler to cab rubber seal is in good shape, fuel vapor/smell shouldn’t be an issue.
You are correct about the trans spark switch I had forgotten about that. Mine didn’t/doesn’t have it.
Here’s a picture of the sending unit setup his truck likely has.
I do agree there isn’t a huge issue against adding a canister (other than gathering the necessary parts) but it’s likely his truck didn’t have one originally.