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MG MGB Technical - Hot start problems

My '67 MGB has become a bit balky lately. It starts well enough, and runs well, but after a run, won't start again until the block cools below 180 degrees or so. Feels like an airlock, but I'm not sure where that would occur.

Back story is that the car was driven only a bit for a couple or three years, and was having trouble idling until I drained and replaced the contents of the tank this spring, and added some fuel stabilizer.

A mechanic friend has suggested a new coil is in order. Any thoughts out there?
J Stirling

Try a new condenser first.
c cummins


Hi J,
You seem to think this is a fuel problem, can you smell petrol after excessively trying to start car if so it could be the fuel mixture is to rich, if so check air filters for being dirty and blocked,
Check auto choke for working correctly check at base of auto choke
Water jacket getting up to correct temperature if you think it is then it could be auto choke slightly out of adjustment loosen of gated screws and rotate anticlockwise a small amount and see if engine starts if it dose tighten down gated screws.
If it still won't start it could be fuel evaporation due to engine heat and poor heat guard insulation and this may need checking out.

Regards Patrick
P.T. Tighe

Why don't you check if you are getting a spark at each cylinder at the right time before throwing parts at it?

A 67 shouldn't have an auto choke i.e. a single Stromberg but twin SUs. Check your choke control really is pushing the jets back up when pushed in ... that is, if you have to use the choke to cold-start!

On heat soak the fuel in the float chambers will expand, push the float valves closed, then further expansion may push fuel up the jet pipe and into the engine, rather than out of the overflow. This will obviously cause a rich condition, and difficulty restarting. This can usually be overcome by flooring the throttle while you crank, but be ready to release the throttle when the engine catches.

A lot is talked about fuel evaporation and vapour lock but apart from one instance this can't really happen in an MGB. Even if the float chambers have emptied due to evaporation from heat-soak (although that takes quite a long time), when there is no fuel in the float chambers the floats will drop and open the float valves, unless the valves are sticking closed. If the pump is working properly it will chatter as it pushes fuel to refill the float chambers. You cannot get pressure from the pump, open float valves, and some kind of air-lock between them. If there is no clicking at all from the pump - assuming an original SU type - then the pump may be failing. You can check this when it won't start by removing a fuel feed pipe from a carb, directing it into a container, and turning on the ignition when it should pump copiously. Be aware that the pump will be pressurising the system for a while after switch-off, so you may get a spurt from the hose as you remove it.

The exception is that on HS SUs (as on a 67) with the separate float chamber and the exposed jet pipe you can get vaporisation in that, but that should only happen if the heat shield is faulty.
PaulH Solihull

This thread was discussed on 01/11/2012

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