Pump woes ...
by David Bolton

“… is this a warning sign of more problems to come?” I asked at the end of the ‘tale of ignition woes’, alluding to the fuel pump stopping in our 1972 MGB which had been comprehensibly renovated in 2005/6. The short answer is ‘Yes’!

In August, on leaving the Hamsterley Hoppings, after a great day out, and before we had cleared the village the engine gave indications of fuel starvation. A convenient stopping place was nearby so we pulled in. Indeed, there was no petrol being delivered to the front float chamber and there was a silent pump. Other MG-ers stopped to offer assistance but we felt we were on top of the problem so they proceeded home; our thanks to them. A sharp tap on the pump and it chattered back into life delivering fuel; the engine immediately fired up again. Great!

This scenario was repeated about 300 yards further on at the village edge, only this time we coasted to a halt, powerless. Fuel starvation again. Oh no, and a long way from home! No pump clicks could be heard, so, straight to the pump this time. Another sharp tap & we were on our way, only now it was intermittent forward progress with the engine firing well and then occasionally ‘stumbling’. It did not resemble the ignition problems previously experienced but we soldiered on as best we could but eventually coming to an elective halt in a lay-by thinking that we had got to sort this out. At least it was daylight and not raining – that morning it had “monsooned” so thankful for small mercies. There had been occasional petrol smells and the fuel gauge was much further down than it should have been, thus a leak somewhere giving intermittent fuel starvation seemed likely.

A quick look under the car & bonnet confirmed that there were no fuel pipe delivery leakages and no leaks around the carbs (twin SUs) or float chambers. With the ignition on and a chattering pump, it was quite easy to see that there was excess petrol being discharged onto the road via the overflow pipe(s) from the float chamber(s). It seemed to be only the front float chamber that was disgorging. The fuel pump stopped chattering when the delivery pipe end was occluded - good. There had been no petrol “spurt” when the fuel line was removed from the float chamber inlet indicating no pressure build-up in the delivery line indicating an “open” end of the delivery which is not as it should be. Thus a problem at the needle valve seat? At this point a fellow MG Club member stopped to offer assistance – he, with considerably more experience, confirmed the diagnosis and then actively helped sort out the problem. The float chamber lid was removed; the float itself was fine as was the float chamber bowl which was nice & clean. Mouth to float-chamber-lid-inlet (ugh!) seemed to dislodge something – and that something was presumably preventing the needle valve from seating & regulating the petrol flow into the chamber. Ha! It is always satisfying to find a cause (& fix!).

Reassembly proceeded swiftly only for the rear float chamber to indicate that it too was flooding. That received the same treatment, clearing whatever it was that was in the needle valve seat affecting the needle seating correctly. The float and needle valve seemed to be working properly with exhaled air when the lid was held upside down. Reassembly confirmed this. The rest of the trip home was uneventful, and it was a pleasure to have the engine working properly although we were on high alert for any mis-beat!

A new SU pump has since been installed and a filter. The old pump seems to work well on the bench and is within all tolerances, but can it be trusted? A fellow MG owner also had similar flooding problems at about the same time, but his float chamber had sediment in the bottom.

Is there a problem with modern fuel and particles? Fall out from the volcanic ash? The petrol tank and all supply lines were new in 2005/6 so it should be unlikely that the particles came from the ‘system’. Surprisingly the original fuel system did not have a filter – the later ones, however, did. Ours now has.

What’s next? I hope there will not be a third instalment for you to read about!