Petrol drain pipe (130)

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djm16
Posts: 34
Joined: Sat May 07, 2016 2:28 am

Petrol drain pipe (130)

Post by djm16 » Sun Sep 24, 2017 3:37 pm

There is a hole in bottom of the inlet manifold centre pot. It has a long pipe attached (petrol drain pipe).

But I do not see a tap on it anywhere. So it remains open to the atmosphere allowing air into the inlet manifold bypassing the carburettor and making the mixture weaker.

Surely there is some mistake here? This cannot be the intended more of operation?

P3Steve
Posts: 123
Joined: Sun Sep 28, 2008 7:05 am

Re: Petrol drain pipe (130)

Post by P3Steve » Sun Sep 24, 2017 8:22 pm

That's the set up on my one too and as far as I can tell from the work shop manual that's the way it supposed to be. There's no mention of a tap of any sort and as you say it must effect the vacuum in the manifold.

I've just had the head off on mine and there was a kink in the pipe and I managed to snap it off while trying to straighten it so I need to cut the kink out and solder a bridging piece but I'm sure its running a bit cleaner now the kink has been removed so perhaps its set up to account for this.

djm16
Posts: 34
Joined: Sat May 07, 2016 2:28 am

Re: Petrol drain pipe (130)

Post by djm16 » Mon Sep 25, 2017 10:30 am

Thanks for your reply. I thought I must be losing it. So goo to know it is not just me!

But how very un-Rover. Even stranger is that with absolutely symmetrical setup dual downdraft Solex, you would think that it would cause the rear pots to run weak.

I had the pipe completely removed, it was in any case a plastic replacement. The engine has been running like cr*p, and I have been struggling to fix why. Blocked passageways in the carb that then blocked again with rust from the tank coming through the fuel filter. Wear in the distributor rotor.

It was not until I noticed a thin wisp of smoke coming from under the carb after stopping the engine that I even realised there was a hole there!

When I have some free time again I am going to try tuning it with the petrol drain blocked off (and then maybe with the long pipe reattached and see if there is a significant difference).

djm16
Posts: 34
Joined: Sat May 07, 2016 2:28 am

Re: Petrol drain pipe (130)

Post by djm16 » Sat Sep 30, 2017 10:25 am

Success! (some at any rate).

The petrol drain pipe seems to have originally been copper. A similar replacement was available form a supplier of parts for AC installations in the form of "copper capillary tube". I bought 0.6mm (ID) and soldered a length onto the existing brass nipple.

It seems the amount of air that can get back up the pipe is negligible. The carb is now balanced with very similar air bleed screw settings. Fuel air ratio according to the meter is a respectable and consistent 13-14 at idle.

The need for the petrol drain pipe became apparent when I was adjusting the throttle linkage and so activated the accelerator pump. Neat petrol was squirted into the manifold and promptly pissed out again through the, wait for it ..... petrol drain pipe.

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