Carb body pipe

[Nigel]

Hi all,
My carb, 34 DATR 2/250 has this pipe, which is blanked off.

Where does it connect to?

Thanks
Nigel

[mangocrazy]

Hi Nigel,

Is that the return to the fuel tank on mechanical fuel pump carbs? I know I blanked off a similar spigot on my DATR when I fitted the Huco electric pump. The mechanical pump carries on regardless so needs a return, whereas the electric pump senses pressure and stops when the float bowl is full.

Graham

[Nigel]

Hi Graham,
No, the fuel return spigot is next to the inlet spigot on the top
section. This is low down just above the base.

Nigel

[mangocrazy]

Hi Nigel,

As I was writing it I thought 'Nigel would know this anyway'...

Graham

[Neil-yaj396]

My carb isn't exactly the same but it has similar take offs for the vacuum advance and a small bore pipe that connects back to the air filter. No idea as to the purpose of the latter....

[JohnFol]

On mine, pipe to vacuum advance is far left, you'll see it connected in my attached image. However I have an additional diaphragm covered by 3 bolts . . .

[squiglyzigly]

Hi Nigel,
Pretty sure that pipe connects to the underside of the air filter housing. It locates on a spur from the block breather hose.

Im not completely sure but I believe it’s to reduce the amount of oil mist entering the air filter housing during idle. During idle the oil mist won’t readily get sucked into the carb and will cause a bit of a mess in the air filter housing. With the pipe connected it sucks some of the breather the mist straight from the spur into the inlet manifold as this pipe is drawn in below the carb butterflies. This is under max vacuum at idle. 

Not the easiest picture to take but here it is on my 2.0 Berlina which also has the DATR 2/250

Ian

[Nigel]

Thanks for all the info guys.

Bottom line is she's not running perfectly, especially
when cold, and still has a flat spot. I've tried various jet
sizes over time, none have really solved the issues. It appears that
blanking off this spigot has no detrimental effect to the operation of
the carb itself.

I'm actually now looking at a fuel injection kit, essentially bolt-on
to the existing manifold, with all the bits required to make it work.

Nigel

[peteracs]

Hi Ian

A bit late on this one, but you are correct in where it goes. No idea on function, but your suggestion makes sense.

Peter

[squiglyzigly]

Hi Peter,
I did wonder if it helped emissions is some way but seeing as the crank breather pipe is already plumbed into the airbox I couldn’t see this being any kind of emission improvement.

Ian

[JohnFol]

It is not just connected to air filter, there is a T piece that takes it to vacuum advance on distributor.

[JohnFol]

Red to carb that you have blocked,  blue to distributor and green to air box

[mangocrazy]

Red to carb that you have blocked,  blue to distributor and green to air box

You have an unfeasibly clean carburettor, John... 

[Nigel]

Hi John and all,
I don't have a Vac advance on the distributor, so there's actually
nowhere to connect to.

And thanks to Peter who brought me back to the basics somewhat.
The goal was to get the thing running better. The float level is now
slightly higher and I've gone back to factory jetting. The difference
is outstanding. She's idling better, the flat spot is vastly improved,
and driving is back to pleasure.
I'm going to continue fettling a little before the trip to Hawkchurch.

Thanks all, Nigel

[JohnFol]

Thank you. Wife not too happy when she saw the inlet manifold in the oven curing the paint.

[mangocrazy]

Thank you. Wife not too happy when she saw the inlet manifold in the oven curing the paint.

I recall similar when using the airing cupboard as an impromptu spray booth. There was nothing else in there, but...