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MG Midget and Sprite Technical - stalling at low revs when hot

I have fitted a Simonbbc electronic ignition kit to my other wise stock 1098 mk ii.

It starts and runs a dream most of the time. However when it gets to around 210 ish and I have to stop for lights or stop start traffic the revs will drop and the engine will stall. Thankfully it will start again at the first turn of the key, but I have to increase the revs to keep it going.

Any ideas on how to resolve
Tony Brough

I would be suprised if that's anything to do with the SimonBBC set up. If you are reaching those sort of temperatures there could be a lot of other issues, like fuel vapourisation under a very hot bonnet.
My normal running temperature is about 170/175. If it got to 210 I would start to get concerned about how close that was to boiling even allowing for a pressurised system.
Graeme W

I don't think the problem is the bbc set.
Though have you re set the timing after fitting the kit?

210 is a bit on the high side. When have you last flushed your cooling system?
Onno K

Cue Nigel!
Graeme W

It could be your front springs....haha

Prop
Prop and the Blackhole Midget

Thanks for the replies.

Yes the timing has been reset since the electronic ignition was fitted.

The car normally runs at about 160 - 190 with oil pressure not above 60 - 70 but in the heat and slow moving traffic is when it gets hot.

I flushed the system about 2 years ago, so hopefully it is still ok. I will give it another go when I get back home.

I suppose because of the temperatures it could be vaporisation, but wither heat shield fitted this isn't something I have suffered from.

Tony Brough

Thanks Prop you could be right again. ;-)
Tony Brough

Fuel doesn't have to vaporise for warm temps to cause a slight problem like this. The hot air is less dense so carries less fuel. If your mixture is slightly lean then the revs may drop sufficiently for a stall. And it will be worse if the carb spindles are a bit worn. Try richening the mixture very slightly - just one or at most two flats on the jet adjusters.
Guy Weller

Do your carbs have the little push pin ... if so id warm it up to normal in the normal weather you experiancing this and then push those pins as in haynes and see what happens, that would tell you alot

If the engine revs up then falls to normal then you know its electrical, if the engine revs up then falls out and dies... its to lean, and the opposite for to rich

Probably a cold air pipe to the carb from the front of the car would do wonders

Is this just a temp issue that only happens during the 6 weeks of summer ???

Prop
Prop and the Blackhole Midget

Thanks Guy

I adjusted the mixture slightly as you suggested SOS hopefully it will help. That said since the temperature has dropped to early 20s rather than early 30s The engine isn't getting anywhere near to the temperature it was at the weekend.
Tony Brough

Have to agree with Guy as experienced similar symptoms and cured by enriching the mix. SU manual tells all. Yes backflush rad and change coolant and check valve clerances.
Mark O

Your coolant should be getting nowhere near boiling.

Do you have an electric fan? If not then your cooling capability is severely compromised at low speeds.

What is the provenance of your rad? If unknown then a flush or reconditioning may well be called for. A radiator can appear to be in good condition but actually be operating well below its potential.

(I'd fix the cooling before looking at anything else though of course a weak mixture or excessively advanced or retarded ignition can also cause overheating).
Jeremy Cogman

Tony,
I offer notes on my simple but thorough cleaning of the cooling/heating system, one or two on here have found them useful

the notes offer two stages, I last cleaned my system 5 years ago but not as thoroughly as I have very recently

I carried out the more thorough stage (or totally OTT to some) this time and was both at the same time pleased and a little disappointed to get very little grit and no crud or muck out

what did surprise me was how much of the old coolant remains in the system after draining, I realised it does but was surprised by the amount, in the heater matrix obviously but also in the engine block, the bottom metal rad pipe (as mine doesn't have a drain) and the radiator

even when I had the rad out and was turning it always and draining from all directions there'd always be a bit more to come out

I was also surprise by how much straw was trapped between the cooling fan and rad and the amount of fly bodies filling the gaps in the rad fins

if you want the notes just email me
Nigel Atkins

This thread was discussed between 26/07/2014 and 29/07/2014

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