Moss Motors, Ltd

Hi every body i am fairly new to the MG world. I have a 77 B that keeps loosing its fuel prime every time it sits for more then 15 min after i shut the car off. I don't see a fuel leak any where so is if possible that air is getting in with out fuel getting out? What should i be looking for?

Lonnie - Check for air getting into the pump through a leak on the inlet side of the pump.  the best way to do this is to remove the fuel line from the carburetors, insert it to the bottom of a catch container and turn the ignition on.  If you see a stream of bubbles coming through with the fuel, that is where the problem is.  Common places for air leaks are a hole in the pickup tube above the level of the fuel in the tank, a loose fitting where the fuel line attaches to the tank,a split in the line from the tank to the pump, loose fittings on the pump or a failed gasket under the large domed cover that is held on with a single 2BA screw, on the side of the pump body.  These are the more common areas for an air leak.  A very uncommon area for an air leak, but always a possibility if the pump an original SU fuel pump is is a split diaphragm.  If there is no air bubbles coming through with the fuel, then a possibility is a torn inlet valve reed.  If your pump is a SU pump and you need help troubleshooting, you can contact me at SUfuelpumps@donobi.net.

Lonnie-

Dave's answer is good and he definitely  knows his stuff.

I wonder if you have the heat shield in place for the carbs?  Could be the fuel is boiling out of the bowls from the heat of the engine while it sits.

LCJUTILA 

Lonnie-

An additional thought.... If your fuel line is too close to your exhaust manifold it can get too hot and cause percolation of the fuel and the symptoms you describe.

Hope this helps!

LCJUTILA