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MG MGB Technical - Over flow pipes

Hi Everyone,

Quick question for you guys. I have a pair of HS6 carbs. There are two pipes on the left fuel bowl and only one on the right. When connecting the fuel lines it seems it pumps from the left fuel bowl out into the other pipe which should be connected to the other carb which has the single pipe inlet. Is this correct? I do not see where the overflow pipe connections would be? Can anyone shed some light on the subject ?

Thank you,
James
james

You may have one carb with an incorrect float bowl cover. Ther should be both a fuel connection and vent connection on each
John H

http://paltech1.com/_wsn/page4.html

The top pair of carbs is what the setup looks like, as you can see there is only one spigot on the right carb.

James

A quick look inside the top covers will answer this, or a phone call to the vendor. The float chambers must be vented to allow the fuel to flow in.
Stan Best

Some SU float bowl lids especialy the ones found on some midgets/Sprites, only had one brass tube for fuel intake, but had a aluminum dust cover on them with a drilling in the lid for venting, if your lid has this aluminum dust cover piece, snap it off and you will see the vent hole.
Hap Waldrop

It's HIF carbs that have different ports on each carb - the left or front carb has an inlet, an outlet, and an overflow. The other has just an inlet and an overflow, with a blank where the outlet would be for triple carbs.

HSs - if they have the separate float chamber - should have an inlet and an overflow on each lid.

The vent actually allows the float to rise when the fuel is coming in. Lack of a vent doesn't stop the fuel coming in, it stops the float rising to shut off the fuel when the float chamber is full, and fuel is pumped up out of the jet and down the carb throat. Acting as a vent is its primary function, acting as an overflow is a secondary function, and that applies to both HS and HIF carbs.

As that site specialises in 'custom' carbs then maybe there is a hidden fuel inlet or vent. Each float chamber must have both.
Paul Hunt

Yes im pretty sure it has the vent hole. I am at work at the moment. Im just curious about how much fuel will be spilling from them. Im a little overly concerned. I have an uprated fuel pump from when I was running webers. I have a regulator and gauge setup. It is below 3 psi. But the gallons per hour is uprated as well. I have a new fuel line from tank to carbs but I am concerned with sediment that may not have been fully drained from the fuel tank, possibilities of the fuel having a slightly tinged rust color etc that could over time clog the bowls and lead to overflow. Will I be safe ? Etc...

Thank You,

James
James

Hey Paul,

Didnt see your message when I posted. So it is pumped out of the jet and down the carb throat. I ran my finger in the carb throat and did feel some fuel. I am going to have to check when I get home tonight again.

A story for you all. I had a litte bit of dislexia when I turned the fuel pump on for the first time to check for leaks. The regulator when coming to the carbs is split so I can run two lines. I had one to the left carb and one to the right carb. I had the remaining barb on the left carb running as a overflow. I turned on the pump and heard a waterfall. Took me a second to realize what the hell was going on. Had a nice little fuel spill to clean up. I thought it was flooding the carb like something I have never seen or heard of for a second before I realized I was absolutely retarded.

Thank you,

James
james

There shouldn't be *any* fuel coming from the vents/overflows. If there is either the float is stuck or sunk, the float valve isn't closing off properly, or the pump pressure is too high and overwhelming the float valves. This last happens with a number of after-market pumps, the pressure should only be in the order of 2 or 3 psi, and if higher you have to fit a regulator (as you seem to have done). If you have any muck in the fuel then you should fit a filter. Staining i.e. very fine sediment shouldn't cause overflows unless severe, but particles will. If the contamination is very bad it will obviously clog the filter from time to time which will need replacing, which is when you would need to consider a replacement or flush and seal of the tank, and flushing of the pump and lines. Sealing the tank can cause its own problems, there is some stuf you can pour in and swill round, but that has been known to clog the pick-up strainer.
Paul Hunt

Its a new fuel line. What I was explaining was that I did not connect the fuel barb coming from the left carb to the right. So it was pumping out of that hose like it should have been doing. I just did not have it connected and it was pumping fuel out onto the ground from what I had mistaken as the overflow pipe.
James

With you - single feed pipe to one carb and that feeds the 2nd carb, just like HIFs then. Should still be a vent/overflow port on each carb i.e. a 3rd port on the left carb and a 2nd on the right.
Paul Hunt

This thread was discussed between 23/10/2008 and 27/10/2008

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