Carburetor vent routing

[jcwren]

This is fundamentally the carb I put on my '70 L6. Should I add a length of fuel line to this vent tube to it route somewhere it won't drop on the headers if it overflows? And would you expect it to overflow under normal conditions, or only if the float valve gets stuck open or something odd like that?

The truck had an Offenhauser triple carb intake installed, and three uninstalled remanufactured Tomco single barrels similar to this one, but without the electric choke. It also came with the the factory single carb intake.

I swapped back to the single carb intake and bought a single barrel carb with electric choke to get it up and running. Setting up the linkages on the Offenhauser intake was too much trouble before I was certain the engine was solid. And while a set of triples would be pretty cool, I'll likely sell that setup and go to a single 4 barrel.

I will say this little 250 with the headers and glasspacks on 2 1/2 inch exhaust sounds pretty damn good

[Steeveedee]

That vent should be routed to the vapor canister on your truck. If that is missing, you are going to have to do something else, not sure what. Maybe somebody else can chime in on that. You should not be seeing fuel come out of that vent unless the carburetor is flooding, though potentially a hard enough stop might get some fuel to slop out.

[jcwren]

I don't think the vapor canister was added until either late in 1970, or 1971, when they went to the vented fuel tank. Mine has no canister, and the tank was unvented (pulled that out and put in a Boyd Welding in-frame tank).

But it does sound like I should just make sure it wouldn't drip anywhere hot.

[Steeveedee]

According to my manual, all 1/2T 1970 292 6 cyl had ECS, which is the Evaporative Control System. If you put in a different tank, you won't have the vapor separator, since it is inside the cab and is now disconnected with the removal of the in-cab tank. The nipple on the top of your carb had a hose that went to the vapor canister to collect vapors as they evaporated from the carburetor. The tank had a non-venting cap because the vapors from the tank went through the separator to the canister. Your vapor canister appears to have gone missing. It was a Federal emissions requirement, which means they all got it. Many have been removed over the years. I just know how it was when new. Maybe look at how it was done in the older years and copy that?

[jcwren]

My tank had a vented cap, no provision for a vent on the tank, and there are no holes in the cab where the vent line would have run. That being said, you mention that all 292's had ECS (although it's actually called EEC), but mine is a 250. Not sure if that would make a difference or not. I do read that '70 was a transition year, and not all 1/2 tons had EEC. They didn't specifically mention which engines.

Which manual are you looking at? I have the ST-133-70 Chassis Service Manual that I use for a reference.

[Steeveedee]

I was looking at my Chilton's. I thought I saw that you had a 292, for some reason. In any event, the 250 CI six is similarly equipped. I got the electronic version of your manual off this website and see that they call it EEC, where Chilton calls it ECS. That's a moot point, since your tank is different, and doesn't have anything now. It may well be that the canister was California only in '70. I was under the impression that 1/2T trucks got it regardless. Guess not.