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MG Midget and Sprite Technical - Hot starting problem

I have recently restored a '67 midget and fitted it with a 1398 cc engine running on original SU carbs. Goes fantastically but if you switch off and leave it for 10/15 minutes or so, it won't start. It will eventually but it is a real pain. Any ideas?
Richard Tinkler

Fuel evaporation? Make sure you've got your carb float bowls really well shielded from the exhaust manifold. It can be worse on an engine with a uprated manifold.
Nick

I have the same problem with mine and thats after wrapping the exhaust manifold and putting a heat shield under the weber. Next step maybe a vented bonnet and an electrical fan ducted from the front to the carb. Oh happy days.
brian

I don't have the problem with any of our Midgets, but do have it with the B. I have a suspicion it is flooding caused by fuel expansion in the bowl, particularly as giving full throttle while cranking seems to help with getting it started. It is worse with the Weber, but still an issue with the SU's. I've been down the route of needle valves and heat shields, but very little improvement.

It seems to be worse with std cam timing and less of an issue when the race camshaft is fitted. Given that it has 12:1 compression and that the engine spins much easier on the starter with the late closing valves of the race camshaft, I'm left thinking that the extra drain on the battery when the std cam is fitted is causing a weaker spark due to the extra voltage drop.

I've fitted a ballasted sports coil, effected some improvement but the problem is still there.
Paul Walbran

"""""a 1398 cc engine running on original SU carbs. Goes fantastically but if you switch off and leave it for 10/15 minutes or so, it won't start. It will eventually but it is a real pain. Any ideas? """"""""""

yes.

More than likely fuel percolation and evaporation in the very small SU float bowls. An electric fuel pump with no more than 2.75 psi fuel pressure at the carburetors. The SU 's do't have an accelerator pump as such and starting can be problematical with heat soak.

you might also use heat sleeving covering the incoming fuel line in the engine compartment and also some tin foil (sanwich wrap stuff) crinkled up and "molded" around the float bowls.
NLA

I think that we may be onto something: My son has a 1275 with a 300 cam and 12:1 CR and it starts easily, so does our BGT race car. Both have SUs and Facit electric pumps. I also have a Marcos 3 Litre Volvo with a mechanical fuel pump & Strombergs and a '37 TA with SU carbs & pump that both have a hot starting problem. So maybe, it is a problem associated with unleaded petrol and old SU pumps. Maybe there is not enough pressure to compensate for the evaporation?

I will get a Facit pump fitted and see what happens.
Richard Tinkler

This thread was discussed between 09/05/2008 and 20/05/2008

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