Vapor return line

[Just Joel]

My 71' wagon 510 is equipped with a vapor return line and I recently bought and plan to install a set of su carbs. The carbs came with the tubes that run from the carbs, down the engine block and dump out by the oil pan eliminating the need for a vapor return. My question is, is it ok to eliminate the vapor return line and run the dump tubes or will I see any negative effects from doing so? I don't mind running a vapor return but I like the simplicity of the dump tubes. Some pros and cons of both setups would be much appreciated.

 

Thanks

Joel

[MicroMachinery]

I don't see how you're going to run dump tubes down the engine block from the carbs and not burn them on the exhaust manifold. :unsure:

 

Why not just re-route the dump tubes to the vapor return line?

[Logical1]

I have a set of Su's in my L18. I Wonder where exactly do the tubes on your SU's come from? From what you describe it sounds more like your float bowl overflow lines. They should just breath to the atmosphere and are not part of a vapor return. I run a return line from a 'T' connector the supply's both my carbs with fuel and then pushes excess fuel back to the tank (helps relieve vapor lock) If you can post up some pictures of your setup :)

[datzenmike]

I agree. The vapor line from the tank is just that. The vapors are drawn out of the tank and into the intake manifold to be burned. It connects to the PCV system. Later models had a charcoal canister to collect and save the fumes until the motor was started.

[Just Joel]

The carbs aren’t on the car yet otherwise I could post a couple pics. I'm referring to the "over flows" that are connected to the copper tubing in Jun's setup...

 

 

I guess I now have two questions...

 

Where and how should these be routed?

 

What do I do with the return line that was utilized by the stock manifold/carb setup?

 

Sorry if the answers are obvious... I'm new to su's.

 

Thanks

Joel

[DISLEXICDIME]

if you hook those lines up the carb's will vapor lock or ar least act like they are vapor locked

[Logical1]

Most people just let the float bowls breath to atmosphere, overflowing is pretty rare. I put small free flowing filters on mine so dirt/debris wouldn't get into the fuel.

 

For the return line you can just ignore it or hook up a system that return unused fuel back to the tank. If you use the stock fuel rail that feeds both your carbs from the single fuel line I put a 'T' connector in between the rubber hoses that connect to the carbs and hooked that up to the return line. I'll post some pictures of my setup tomorrow :)

[Just Joel]

That makes more sense. The vapor vent and overflows are two different systems all together. So venting the overflows I can do. For some reason I thought these two systems were the same. Sorry...

 

After some more reading I think I have a vapor vent line, not a return line. Like Mike said, it burns the excess tank vapor after start up. So, the new question is... do I still need this now with the su's and where would I hook it up if I do.

 

Thanks

Joel

[Just Joel]

Some good info here as well. If I have to keep it, where do I hook it up on the su's.

 

Thanks

Joel

[jun]

Hey Joel,

 

Just to clarify my setup:

 

those copper lines are for the overflows, as you already know. While some people don't run overflow lines, all it took for me was one experience where one of my floats developed a small crack and filled with gas. That was fun as one of the bowls overflowed, and started trickling gas onto the manifold. Luckily nothing happened, but I wasn't taking chances. After I repaired the crack and triple checked both floats, I made those copper overflow lines to dump fuel away from anything hot in case it happens again.

 

Regarding the vapor vent line, this is a hard line that's near the brake master, right? I used rubber tubing and connected the other end to the backside of my filter as it had an inlet. That way the vapors are getting sucked in and getting burned.

[MikeRL411]

The fuel overflow lines hook up to short lengths of fuel hose. These hoses route downwards to fittings [really perforated tabs] attached to the oil pan under the boltheads for the rear and to the left front A arm [yes, 411 and roadsters have A arms, 510s have McPherson struts] for the front carb.