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MG MGB Technical - Fuel Line Leak

So there I was, proud as punch tidying up the inside of the GT (a '71), when I thought, I 'll fire it up, and let it idle before I take it out.

Normally, fires up fine, and idles OK, although it needs a bit of choke just now, being a bit chilly here in Scotland. But starts running REALLY rough. I get out and have a look in the engine bay, where petrol is spraying from the fuel line running accross the carbs (the line that connects the 2 float chambers.

On closer investigation, the PO had put 2 holes in the fuel line, so I replaced the line. The car then wouldn't run at all - too rich I think. So I patch up the old line, and again, it struggles. So this time and cut a smaller hole in the patch I've made, and hey, it runs like never before.

So, here's the crunch...

Why cut the hole in the line - is it not easier to have a fuel line with no holes to draw in air and get the carbs to run leaner (if so, what do I need to do?)

Alternatively, I could fit a pair of K&Ns, and as they would draw more air, it may run OK.

Do I just run with the dmaged fuel line (I know the answer this one, but can't understnad why the PO decided this would be the way to go).

For my own info, what does this fuel line do - I assumed the line from the filter to the carbs was the main fuel feed?

As usual all help gratefully accepted.

Thanks in anticipation.

Derek
Derek Meldrum

I think you've got yourself in a bit of a muddle there.

Holes in the fuel line won't draw air in, instead fuel will simply be wasted. Pressure might be a tad lower if your fuel pump can't keep up, although at idle it's probably fairly close to normal.

If it's too rich, move the jets up!
--
Olly
Oliver Stephenson

i see two way to go: replace fuel line or buy a really big fire extinguisher. If the carbs seem to be running rich after replacing the fuel line, then you need to adjust the mixture. Based on what you said, I would start by checking the float levels, then move on to adjusting the carbs. Take each jet and adjust them up until they are flush with the top of the bridge inside the carb. Then turn the nut two full turns down. That should be a good starting point. In the General Section there was a thread about on-line manuals. Here is the link. http://www.1978mgmidget.com/manuals_and_booklets.html

Download the Tuning SU Carburetters. It will tell all you need to get the carbs set the right way.

Jim
Jim Lema

You say "I assumed the line from the filter to the carbs was the main fuel feed" which would be correct which makes me think the line with holes in is *not* the fuel feed line but some kind of PO bodge to connect the two overflow pipes together. Originally each (HS) carb would have had its own overflow pipe going down beside the engine and open to the atmosphere. If is *is* the overflow pipes and fuel *is* spurting out of them then one or both of the float valves is not sealing and the float chamber is overflowing. This will cause a rich mixture, and blocking off the holes will cause an even richer mixture. As long as it *is* the overflow and *does* have holes open to the atmosphere it should be OK, you need to be investigating the float valves, probably replacing them, but the float(s) could be punctured and fgull of fuel, or an aftermarket pump could be supplying too much pressure, or you could have a rusted tank and dirt in the (otherwise sound) float valves.
Paul Hunt

Thanks guys. The line I'm referring to links the 2 float chambers together, and runs over the air filters (2 pancake filters presently fitted).

This line had 2 holes in it, and like you say Paul, may have been used to vent fuel to the atmosphere.

I'l need to investigate the front float chamber, as this was where the fuel was coming from.

Thanks again,

Derek
Derek Meldrum

This thread was discussed between 16/10/2003 and 17/10/2003

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