Mechanical Tips for MGB Members

A Tale of “Ragged Running” by Don Bishop

It’s a matter of pride to me that my GT engine runs a smooth as a nut; or as near an approximation to “s.a.a.n.” as you are likely to get with a good old “b” – series which hasn’t had the benefit of balancing etc.. What I really mean is that it pulls like a train with equal compressions and no misfiring. Normally, that is – it normally runs etc. etc.. Until a couple of weeks ago when I happened to be on a trip across to Weston -on – the – sea (aka Weston super mare) and having my son as a passenger – of itself a rare occurrence as 1) he lives in the USA and 2) he’s more of a Triumph man anyway (says a lot for my parental influence, dunnit?) when IT happened.

We’d just climbed a short sharp hill near Yeadon and come over the top to be greeted by a T-junction and a marked loss of power, in that order. Took the corner and bowled way downhill with a return of said power, no apparent further problem. Spent the day with friends, motored back with n.a.f.p. until we reached the M27 near home when I started pressing a bit harder to keep fairly well up with all the traffic doing 80+. Alls well for about ½ mile when came a vibration which felt for all the world as though a back wheel had gone badly out of balance. There was bags of noise anyway, what with the open sun-roof and windows, cassette player and so on. I eased off the loud pedal a bit and everything returned to normal with a reduction of only about 3 mph. I thought about it and resolved to sort it out soonest, Expatriate son was offering all sorts of suggestions, of course – the sorts of things that might well happen on a Triumph, most totally ignorable of course. Dreadful thing pride y’know.

Anyway, what could it be? I looked at my service records and noticed that the spark plugs had done nearly 20,000 miles so a new set wouldn’t come amiss. The leads all looked quite good with no bad miss-routing to cause possible arcing. Out with the distributor, may as well do the job properly. The points looked quite badly pitted so in went the spare ( new) set. Could it be the condenser? No real way of telling although in my experience condensers don’t usually cause intermittent problems: they either work or they are dud. Change it for a new one just in case. Cap and rotor arm looked fine – no signs of arcing anywhere, inside or out. I would stress that changing the plugs didn’t cure it, having road tested it at each step. Neither did the points-and-condenser change (OK so that’s two steps but it was easier to do both together while the distributor was on the bench.) How about the coil – could it be breaking down under the heat and stress (don’t we all dear?) I will say at this point and in my own defence that the car did seem to be running a bit better than before, so the ignitions renewals might have been overdue; but again, when pushed, the misfire came in and it felt as though one carburettor was giving up it’s share of the work but returning to the fray when the throttle was eased back.

Wait a minute, there’s a clue. When under hard acceleration the power was on tap for a few seconds but fell away with the onset of misfiring. Could it be fuel starvation? New pump last year should be up to the job. Come to think of it, on early morning start-up I had the vaguest impression that the pump had taken to ticking very slowly instead of setting to with a will. So – disconnect the fuel pipe from the rear carb., put a tray underneath it and switch on: result – a dribble. Then (but not before) I remembered that little extra I’d fitted quite some time ago, in the form of a small in-line filter, hidden out of sight (and mind) round behind the washer bottle on the near-side scuttle. Sure enough, it was chokka-blooming-block with rust and sediment, wasn’t it? No wonder that not much juice was getting through when heavy demands were made; but just enough when cruising on a light throttle (here be nasty thoughts about the state of the bottom of the tank.)

So it was back on the road, reassured that all should now be well. And it came to pass for about five miles, when we suddenly went onto single-carb. Mode again; but this felt different because the misfire came at tick over particularly, accompanied by a strong smell of petrol and much ticking of the pump – obviously one carb. Was now flooding due to an over abundance of go-juice. So it was a quick peep underneath to see which overflow pipe was dripping (after switching off course;) and remove the float-chamber lid of the offender, in this case the front one. The out with the spindle about which the float pivots and catch the needle valve before it hit’s the deck. Blow through the pipe feeding the valve, where it just had to be a chunk of rubbish, disturbed by the previous work, holding the valve open instead of it being closed by the pressure of the float upwards. Reassemble and drive back home with no further problem, then take the float-chamber lid off again and put a new gasket on (you’ve got spares in the shed/garage of course, haven’t you?)

Now that’s a whole lot of words to cure a simple problem or two. “A bad case of fuel starvation caused by a blocked filter, followed by a flooding carburettor caused by some of the same dirt that gave rise to the original starvation.”
There – not half so much fun, though, is it? And the ignition system’s had a birthday to boot. Now the car “standeth not upon the order of its going.” Runs well, too. (Retires, humming “If I can help somebody as I move along……….”)