Weber 34DAT Fuel Return Pipe? Anyone know where it attaches?

[lowdown8]

Hi, I have replaced my pierburg as it was completely shot, no problems there, my new weber carb is fine, (bought from weber, the replacement already jetted for this model).

I am a firm believer in the weber and the pierburg and know the ups and downs and know all previous discussions about them, but this isn't about that at all.

When I fitted my new carb according to the weber instructions, I found nowhere to attach the fuel return pipe to on the actual carb.
A local mechanic couldn't work it out and said "Don't worry you don't need it, just seal the pipe off with a bolt" as the carb will throw any excess fuel out, so I did.

However, as my carb ran fine, I thought it no problem. But recently I have had three seperate occasions where I have lost power, or backfired considerably and then had to pump the throttle to get anyhere slowly for a couple seconds and then suddenly full power kicks in and then gone again. 1st time after a long run around all day except when I came to a junction a mile from home, the second when pulling out of a car park (still very warm engine), not enough power to even get out the car park without my foot to the floor (highly embarrasing), third driving along for an hour before it just happened, backfired, pressed throttle, no power more backfiring until I was able to pull over..

PANIC PANIC PANIC....HOWEVER...
Pulling the van over, Switching off the engine, switching on and revving a couple times and all is back to normal, with glorious full power for the rest of the day.

When this problem happens, It feels like it may be over-fueling or too much fuel in the carb or something as the accelerator will take a couple seconds to kick in, and then erratically with some backfiring. One instance was particularly bad for backfiring (I checked the throttle cable, so not that.) On one occasion, I pulled over, switched off, switched on and didn't even have to rev it to fix it.

I am going to put a second fuel filter on the fuel pipe just before the carb in case it is a fuel contamination issue, but I don't think it is.

Has anyone had this issue? I have checked all my vacuum pipes, everything is nice and new and no leaks, The extra bolt hole in the air filter is sealed, so no air leaks anywhere.

Just missing a fuel return pipe opening or somewhere to stick it. I would assume without it, there would be a loss of pressure issue?

Any ideas or help would be greatly appreciated, as although the van runs fine 95% of the time, this problem puts a major downer on the day when it does happen (at least for me), as I have my wife and two kids in the van when it happens and we are normally on a day out.



- Jay.

[T25Convert]

Hi,

I has a webber 34 on mine. The fuel return is next to the fuel inlet. I guess that yours does not have the return fitted, as you really can't miss it!

I'd have a chat with the supplier, as it seems that something really isn't right.

Cheers,

Alex

[lowdown8]

Hi, Thanks for your help.

Yea there is an opening on the left next to the fuel inlet but it looks sealed up inside, and I wouldn't know how to connect a pipe to it anyway as it an opening not a nozzle? Does this make sense?

Any further help would be greatly appreciated. - Jason.

[T25Convert]

If there is a small 'hole' that doesn't lead anywhere then your carb has not got a fuel return - this hole would be drilled out and a brass fitting similar to that of your inlet would be fitted. So, to my mind, this is not the correct version of the Weber carb for your van....

For your reference here is a good picture of a DAT34 with the correct in/out fuel arrangement http://www.fiatparts.com/34DAT.jpg

As I see it (and others may disagree) your mechanical fuel pump supplies fuel at a rate governed by engine speed, as it is driven by a pushrod of a cam in the engine. As such, you get very approximatly the right amount of fuel arriving at the float chamber at any given time to keep up with engine demand.

However, at times there is too much fuel being delivered compared to demand (e.g. when going down hill using engine braking). On a carb with a fuel return this then gets returned to the tank ready for re-use. However, where is your excess fuel going? Without studying the exploded sections I'd guess either through the jets (very rich running) or out the float chamber vent.....

Ignoring the weber/pierberg debate, I would suggest that this weber really isn't fit for purpose. I would get in contact with the supplier and ask them to replace your carb with the correct fit for purpose model for your van.

Let us know how you get on.....

Cheers,

Alex

[lowdown8]

Hi, I had a reply back from the supplier, he is a Webcon Distributor.

I believe I have a webber DAT34 II, so it might very well be a modification.

Here is his answer:

"in the kit was a Tunion with a restrictor. This is put into the main fuel line & the return pipe connected to the restrictor."

I have yet to still find this.

Jason.

[lowdown8]

Hi Again,

Found the Y-shaped Tunion with small restrictor on the end of one tube. Would you possibly understand whether this might be a solution?

Seems funny to have a fuel pipe split with a restrictor to the return pipe? Surely this means the excess fuel has to return down the inlet pipe to be pushed out through the restrictor?

- Jason.

[T25Convert]

Right,

The restrictor 'T' piece will indeed provide a 'fix' to your problem. Basically fuel will be pumped under pressure from the pump to the T piece, where most of it will head towards the carb to fill up the float chamber, and then into the engine. However, some will now divert itself off back down your fuel return line. As fuel demand in the carb goes up, then less fuel ends up in the return line.

Having had a general read up on carbs, the T seems to be a common feature of some webbers (although not normally the 34DAT?), and will "prevent bogging due to excessive fuel pushing the float down" - a quote from a Lancia site. Sounds like a fix for your problems.

Fit it, and see what happens!!

Cheers,

Alex

[lowdown8]

Hi thanks for your help, this is what the weber dealer said;
The original Weber DAT's used had a return in the lid. These have not been available for some time & as a special type of DAT has to be used for the conversion Weber now have no choice but to use what is available. The last batch have just been made & no more DAT's will be available again. So future sales will not be possible.
I would suggest you phone in the morning for guidance in fitment of return to tank.

I will let you know how I get on.

- Jason