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MG Midget and Sprite Technical - Err, what happened there

Managed to spend some quality time with the sprite this weekend. 20 miles into a run I was accelerating up a hill when the car started to loose power. It then started missfiring and backfiring. I was nursing it towards a lay by when it seemed to clear its throat and started running ok again. Not a huge problem as it went on to do another 170 miles without incident, but I would like to know what happened. Rev counter stayed steady and as far as I know an ignition fault tends to stay a fault untill traced and fixed. I have a fuel filter fitted so I dont think it was cack working through to the carbs. Any other ideas?

Cheers, Mark
M Adams

possibly a problem with fuel pump and consequent loss of fuel pressure?
David Smith

Fuel pick up issue?

Did you go up any more similar grade inclines on the remaining 170 miles?

We had a tank where the fuel pick up pipe (inside the tank) had a hairline fracture in it and had similar issues which would only happen infrequently. If the tank was full of fuel then the fracture was under the fuel level so it wouldn't occur, when the fuel level dropped it would occur but only when going up a steep slope and the fuel level dropped beneath the crack and it then sucked air in.

HTH

A.
Andrew McGee

Almost certainly fuel pump..not providing enough pressure to deliver enough fuel whilst accelerating up a grade.

Mark O

Interesting, thanks for all that chaps. Thinking back, that probably was the longest of the climbs. Might try and replicate the drive next weekend and see what happens.

Mark
M Adams

If the pump is above the fuel line, the pump wont work as well....if you were low on fuel and the incline grade substatial... I could see that being a result


Prop
Prop and the Blackhole Midget

Don't dismiss the pick up pipe in the tank.
Try a long steep hill with a full tank and one with a 1/4 tank.
If it works fine with a full tank and not with less then you need a new tank
As there is no repairing it without opening and welding it and comparing that risk with the price of a new one.....
Onno K

If you had fuel injection without a swirl-pot, you'd have instant fuel starvation round RH bends and up hills with 1/3 tank or less. Carbs keep a small reserve of fuel in the float chambers, which cover 99% of most road situations - but this small amount of fuel can't last for ever when the pump is pushing just air.

Anthony
Anthony Cutler

How about water in the tank? Condensation? Had the car been sitting a long time before the last fill up?
Could have been anything but Ive experienced your symptoms when I buy gas at a certian filling station I no longer go to. I know mine ws water in their gas.
Steven Devine

My 1500 did this because of too much fuel i.e. the carbs were flooding (now fixed) but I go with the lack of fuel explanation, however the backfiring worries me, this sounds electrical.
R W Bowers

Hi all. my internet connection was down yesterday evening, so just catching up. Bit more info. The car gets a run out quite regularly, rarely sits for more than a week or so. Inbetween times its stored in a dry garage. would like to think that would rule out condensation build up. The tank was full, having just been brimmed at a shell station with shell v power. The pump is not a standard su. It was one that was supplied by a local motor factors when I was putting it all back together a year and a half ago. Can't remember the make but it was about half the price of the su. The back firing I mentioned could have been more a phsycological issue as things were going pear shaped, the lack of power and missfiring were very real though! That climb was not the longest or the steepest, however it was the longest and steepest combined, if that makes sense.

Anyway thanks for all the input.
M Adams

Could have been valves binding.
Guy W

Hi
If you find that the fault is not the fuel pump then have a look at your coil.
Many moons ago I had a similar problem that took ages to remedy as everything seemed to point to fueling.
It was a shorting within the coil relating to the oil level within so on the flat the car was fine.
Alan
www.masckent.org
Alan Anstead

Hi Alan

The coil should be ok, it was a new unit supplied from the accuspark people a few weeks ago. I do appreciate that you should not leave new components out of a diagnoses, but I think i will look at fuelling first.

Hi Guy

Are there any other symptoms of binding valves to look out for?

Thanks folks

M Adams

Mark,
Sorry for being so brief! At one time I was commuting on a regular particular route which includes a long, quite steep incline needing full power and where I would drive at full throttle for several minutes. Regularly, before cresting the rise the car would suddenly loose power, hesitate and slow down. No flickering of the rev counter so I knew it wasn't electrical, or the coil, although in a way it felt like that. Fuelling seemed Ok.

In the end I discovered it was overheating valves which were sticking open. The cause was overtight tappets. I was using a performance cam but hadn't increased the gap setting and under the extended full power climb, the valves were not cooling sufficiently through the valve seats. Backing off the power for a short while and more gentle driving and it would run again OK.

No guarantee that this is the same problem as yours, but the symptoms do sound similar.
Guy W

thanks Guy, will check valves as well as looking at pump.
M Adams

don't discount pump because it's new, I thought it unlikely a new pump would be faulty in another thread elsewhere and Sod's Law after poster checked loads of other things that's what it turned out to be, the new pump

that doesn't follow that it will be in your case of course and the fact it's not an SU means nothing, I fitted a Q&H electronic pump 5 years ago and it's been fine
Nigel Atkins

This thread was discussed between 20/05/2013 and 21/05/2013

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