MGB: Bad Fuel Pump???

My MGB has been idling very rough and dies if I don't keep some foot pressure on the gas pedal. I have the weber carb and it has been great up until now. I got under the hood to look into the carb while idling, and gas is just barely trickling through one side of the butterfly. When the accelerator pump kicks in, everything is smooth. I glanced at the inline fuel filter and saw that gas was just occasionally trickling into the filter from the line. My filter was never more than 30% full.

When I turn the key, the fuel pump clicks until pressure builds and then just occasionally clicks, as is expected... I still don't get any fuel into the filter. So my assumption is that my carb has only minimal gas pressure, which affects my idle, but goes away when the accelerator pump engages. I haven't had time to crawl under and check the pump.

Is this a carb problem or a fuel pump problem? This weekend I'll dig a little deeper...

Rick

Unless your filter is mounted vertically, with the outlet at the top, it will never get full - it will only fill as far as the top of the outlet!

If the car runs OK at speed, I'd suspect a carb problem....perhaps something to do with the idle circuitry. Dirty fuel filter might cause an idle problem, but I think it would be even more noticeable at speed where the demand for gas was greater. Fuel pump "sounds" from your description like it is working as it should.

What you are seeing in your fuel filter is likely trapped air. Remember, the SU pump quits stroking on pressure so it won't compress that air very much before it stops pumping. It doesn't mean it isn't working correctly or adequately.

mvk66 Wrote:

Vacuum leak has occurred to me as well... the line to the distributor seems to be in good shape. If I unplug it at idle what should happen? Also, it is a weber, not the SU duals...

Rick - See the article, Fuel Delivery Troubleshooting Guide in the SU Fuel Pump Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ for how to test the fuel pump for proper volume of fue delivered.
Cheers,