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MG MGB Technical - Dumb question of the day

I know the technical/mechanical geniuses out there will to think I'm a bit of a lemon for asking this, but here goes...

I've had my BGT for a few weeks now. It's been pretty reliable. Only issues were a couple of non-starts on cold mornings.

Not being very mechanical, I left it in with a mechanic who specialises in classics & is well used to Bs. Got her back yesterday. The mechanic said I got a good 'un. She had been well looked after & just needed to be regulary serviced. He clearly loves old cars & encouraged me to come along for the next service so I could see what needed to be done.

Before the service, the engine chugged along with a bit of spluttering here & there. When I fired her up at the garage, she sounded a lot healthier - less of a chug & more of a grunt. I was smiling from ear to ear as I pulled out of the garage onto the open road. Super... or so I thought.

I had driven her about 1/2 mile from the garage, when she coughed & spluttered to a halt. "Bloody mechanics" I thought. Then I noticed that the problem lay closer to home... in my excitement to get out on the open road, I had negelected to do the only "mechaical" job I was competent to do myself... I forgot to put petrol in & she was empty!

I filled her up, but the car car has been sluggish & has cut out on me numerous times since yesterday. She re-starts no problem, but it is a real nuisance.

So to my question... is it likely that running out of petrol is causing the problems, or is it coincidence? I'm a bit sheepish about going back to the mechanic until I have a better idea if it's my fault or not!
Mark Whelan

Running until the tank is empty can occasionally suck up a bit of grit and block your fuel filter - they're usually transparent, so you should be able to check it visually if it's in the usual place in the engine bay.

Alternatively the lack of fuel may have caused the fuel pump to get a bit muddled, but I've done it plenty of times (MG fuel gauges aren't accurate after 30 years :o) and haven't done any permanent damage yet.

Hope this helps,
Oliver Stephenson

Maybe when you ran out of petrol all the accumulated crud was sucked up from the tank and now clogs your fuel system? A visit to your mechanic seem unavoidable.

It's a bit like drinking "real" tea; always leave some in the cup for the leafs.

A visit to your mechanic seem unavoidable.

Willem van der Veer

I really don't subscribe to the 'run out and you will suck up dirt theory' for two reasons - one I have run out on a number of occasions with no ill effects (only once in one car accidentally, the rest to check the calibration of the fuel gauge after a new sender), and regularly run both of them low, and the pick-up/strainer stays the same level above the bottom of the tank no matter how much fuel is in there, unlike tipping a cup right back and getting a mouth-full of tea-leaves. What *does* happen is that once the fuel level drops below the pick-up the pump chatters away very rapidly until you notice and turn off the ignition, which can take quite a long time (when done inadvertantly) and may have pushed an old pump over the edge. Whilst the ratio of crap to clean fuel is greater when the tank is 'empty', i.e. the fuel level drops below that of the pick-up, than when full it is a gradual and linear progression from one extreme to the other, it does not suddenly get very dirty just as you run out.

Remove a fuel pipe from a carb, direct it into a container, and turn on the ignition. The pump should deliver *at least* one pint per minute with very little by way of bubbles in the fuel stream. That will tell you whether to go back to the pump, or forward to the carbs and ignition.

The other thing with cutting-out is before you dip the clutch, knock it out of gear or swirtch off i.e. when the momentum of the car is still spinning the engine, look at the tach, ignition warning light and fuel gauge. If the tach is still registering revs
then the ignition LT side is OK, but it could be HT or fuel. If the tach has dropped to zero even though the engine is still spinning then the ignition LT has failed, which could be due to the ignition itself or the ignition relay (77 model or later). If the fuel and temp (77 model or later) gauges start dropping as well then it is probably the ignition relay or its connections. If the warning light is on whilst the engine is spinning, but out when it has stopped, even though the ignition switch is still on, then the 12v supply through the ignition switch has failed, either the brown to it no longer has 12v, or the white between the switch and the relay, or possibly the switch itself. And all that without getting out of the seat or even coming to a halt.
Paul Hunt

no oil in the dashpots?
patrick bailey

If you follow the adage of never letting it get below a 1/4 tank and do that for 20-30 years (our cars are OLD guys), you probably will get a lot of junk when you od run out of gas.

However, I've been running mine down to near empty forever and have never had a problem.

Because I am firmly convinced that it is better to suck a little junk over time (fuel filters are cheap) than to have it hit when you finally, for the first time in your life, run out of gas.

And time for a really stupid question. If the fuel pump can drain the tank completely, where do you think the suction is? Right down there in the junk at the bottom...
Richard Smith

The whole point is that the fuel pump *doesn't* drain the tank completely, the pick up is not right at the bottom, so some is always left in, with the rusty bits and water.
Paul Hunt

Paul made my remark redundant.......

And in my youth I was an expert at leaving myself stranded for lack of fuel, Just a note also mark,
When I was in the military they told us "the only dumb the one you don't ask"
Safe motoring to you my friend,
J A Kelly

The guy in the garage should never have let you leave on a empty tank get the car back to him tell him what a great guy he is and then tell him if there is any thing major to phone you first its my bet that your car will be running as good as when you first picked her up within 24 hrs dont forget to give him a tip and all is well
Richard H
ps paul advised me once to return a car that had been in for a tune and came out worse job was fixed within 24 hrs mechanic got a drink and my car is great
Richard H

richard please spend a moment reading eats shoots and leaves

This thread was discussed between 08/04/2005 and 12/04/2005

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