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MG MGB Technical - Fuel Surge

Hi, I'm one week in to a 1978 BGB GT project, the car has lain dormant for 7 years.
My fuel pump after dismantling and reassembly gives me that TICTICTIC noise and then does deliver!, The engine starts and the pump still "Tics" However after shutting down there was a substantial amount of fuel deposited under the sump. It looks like either the pump is over delivering and the carbs are dumping or could it be that the carbs are just leaky? I cant see from the Haynes manual if there is meant to be any pressure relief built into the pump. The previous owner claimed that once pressure was up on the pump it would then run silent.

Chris
domaille@bigfoot.com

Chris
The 78 will have the HIF carbs with integral float bowls with overflows that are diverted into two pipes that converge at a bracket near the forward end of the sump away from the exhaust manifold. Unless you have a leaking hose connector, then it sounds like you have a sticky float in one or both chambers. The older HS type with external float bowl is much easier to sort.
7 years with old fuel in the system will have left a sticky mess. Perhaps if you got some high quality new fuel or a solvent and squirted this in it might help clean the float swivels. Also possible the floats may be punctured.

HTH
Martin

Thanks. I wasn't sure if my pump was a bit to enthusiastic or not.
I couldn't find any reference to the diverter pipes in the haynes manual. I'll leave some fuel in the chambers for a day or so then open up the carbs.

thanks
Chris Domaille

Chris,

The SU pump does not have a pressure relief valve. When it is holding pressure the points in the pump are open and no electric current flows (no ticking). When the pressure drops the points close and the pump operates.
Martin's comment about old fuel is probably your problem. New fuel and cleaning the float valves might fix it.
Does your pump keep ticking when the engine is not running?

Mick
M F Anderson

Yes, I switch on the Ignition and I get a constant ticking. Like you both said, time to investigate the carbs.
Chris Domaille

I agree with Martin and M F, that the old fuel may be gumming up the works. It may do to disconnect the fuel line and spray some carburetor cleaner into the chamber to loosen up the gum.

Being that it has lain dormant for seven years, I'd be suspect of any rubber on the car. Two very important points being brake lines and fuel lines.

Check that your fuel lines have not started to crack, leaking fuel through same.

For a dollar or two you can replace all of the fuel lines. The one in the engine compartment is simple, the two pieces at the fuel pump are a little more messy, but technically very easy and worth the trouble.

And on a different but related note, before you drive the car at all, replace the brake hoses. It's cheap insurance. While you're doing that, let all of the brake fluid dribble out. It's time to replace it by now, and you'd have had to bleed the brake lines anyway.

Enjoy the project.

Matt Kulka

As well as a leaking float valve in an HIF I have also had a punctured float. The float wasn't immediately obvious especially as I had to change the valve on a previous occasion, so I jumped to that being the cause again.
Paul Hunt

This thread was discussed between 26/07/2003 and 27/07/2003

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