Weber carb - Is this a fuel return line? What to do with it?

Hi,

   I'm working on a friend's Mk1 1.6L Cabrio which had a Weber fitted a while ago, a 34 DTMR. These appear to have a fuel return or a vapour vent as opposed to the DMTL which doesn't (I don't think). It came from someone's 1.6L Mk1 previously.

   It runs fine EXCEPT when it has been left sitting for too long, when the fuel fails to get sucked up the lines properly, it just turns over and over with no evidence of fuel getting even to the engine compartment.

   Fuel accumulator was replaced previously anyway and then I replaced the pump troubleshooting this, so no problems with the pump etc (I think the previous pump was fine too after examining it by hand afterwards).

   Anyway, still does it! So I'm suspecting the plumbing of the Weber when it was installed. Here's a photo, the fuel return or vapour vent is highlighted in red:




This hose has been plumbed in to the fuel feed to the pump via a Y-connector. Notice also that the fuel filter has been removed.

My suspicion is that when fuel has evapourated from the carb, this fuel return is a direct line to the outside world and so the pump just sucks air in via this instead of the fuel, path of least resistance !

I kind of tested blocking up this hose - bent it in half and clamped it shut - whilst also installing a fuel filter and it then turned over and started ok. Thing is I'd already spent some time sucking fuel up the fuel lines by then so the test wasn't conclusive. Plus I'm not sure if it is safe to block this pipe and disconnect it.. or should it instead be plumbed to the main fuel return?

Any speedy answers would be very greatful as I want to make sure it can start easily on a journey in a couple of days! Thanks..

And another thing:

The carb whistles a bit.

When I blocked what I think is the return, the whistling stopped…

Just been thinking about this…

… surely connecting either a fuel return or a vapour vent to the fuel line would be wrong whatever? You'd be getting a vaccuum, suction on that connection which you don't want in either case.

I'm going to attach it to the main fuel return to the tank and see what happens! I've a spare bit of fuel hose from changing all the fuel hoses (thought there was a leak) left over and the y-splitter will be free too to use elsewhere.

I have a DMTR fitted to my Mk1 Scirocco and yours is not plumbed in right, the fuel return pipe should not be plumbed into the fuel in pipe!
Mine has the metal fuel in pipe from the bulk head to a rubber hose, to a fuel filter, to a rubber hose, to the fuel pump, to the carb, then from carb to metal fuel return pipe by bulk head.

I don't have a green swirl pot as there was never one fitted in 1978 so I'm not sure how that is fitted into the fuel system or even if it's need?

The air filter fitted to the car wont help as there is no hot air feed when the car is cold and the carb sucks in hot when the engine is hot as it's above the exhaust manifold the orginal air box with a K&N fitted inside is a better mod in my opinion
Only picture I have at the moment but will get a better picture for you.

 

 

Many thanks for that. Just thinking about the fuel return connection, it does seem a bit daft..

I'm not that experienced to be honest but have a mechanical mindset so can make educated guesses once I know what's actually going on.

The weber was installed by a garage and I think the guy must have had brain fade and was just looking for somewhere easy for fuel to flow away. But it ran fine and when it hasn't sat for too long, still runs fine connected up wrongly.

On the Golf carb engines there is a fuel accumulator (also called a vapour separator I think) which comes after the fuel pump so there is a fuel return there too. In reality, the DMTR isn't the correct carb for the golf, the DMTL is I think and that comes with the fuel return blanked off (again, I think). It came from another 1.6L golf engine previously so that was the decider that it would work fine and importantly the jets would be correct. I imagine at a later date and with the right plug bolt thing, the return on the carb could be completely sealed - I'll wait for some expert advice on that though just to make sure.

I'll take the air filter advice on board and see what happens in the winter months.. I'm not too sure that the original box will now fit as I think this weber now sits a little taller than the pierburg. Still have it so can sort something out later.

If you don't mind posting up other photos as and when you have time, that would still be appreciated, help get a better idea of things.

Some more pictures for you of my set up, the DMTR is the correct carb for my car as I had a Zenith carb before changing and I think the DMTL is a replacement for the Pierburg carb?
The car will run without the fuel return fitted but any extra fuel will be sent into the engine if the metal pipe there fitted to car I would connect the carb to as that's how its ment to be set up.
I fitted my carb to the instrutions as it was a new carb.
The standard air box will fit back on but you need to let it sit a little higher on the front mounting bracket, I had to use some bigger washer to grip the front bracket just don't bend it down to much or you will split the rubber flange the carb sits on and that will let extra air into the mixture.
Ive run my in fuel line and filter a little further out away from the hot exhaust just to stop any fuel evaperation.