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MG MGB Technical - hot start problem

hello, not been on this site for a while, but hope to get some help
my car starts and runs perfect even when hot , once i turn the engine off it does not want to start and when it does the engine splutters on low revs
i changed the
spark plugs
dizzy cap
leads
coil 12v (GOLD) standard
my engine as the aldon ignitor fitted

if i leave it foe 30 minutes it then runs fine
my coil seems to be very hot but not sure if thats normal.ive put a new 12v ignition live to the 12 v coil after finding the orig live went through a ballast resister in the loom .
my engine as only done 3000 miles since the rebuild and produces 110 bhp at the wheels due to a 285 cam and peter burgess fast road head thanks .

daz

ive got 12v at the coil but no spark, removed the ignitor 11 , does any one know how to test it thanks
daz

thanks for the help !
daz

I am no expert on this but if you had a ballast resistor fitted I think you should have had a 6volt coil fitted. This has been discussed many times on the forum and if you go through the archives I am sure you will find more info. on this.
Trevor Harvey

Daz
Check the float settings. Also, you could try weakening the mixture slightly. It may be an over rich mixture at idle - not a problem when the engine is cold/cool.
Richard
Richard Atkinson

thanks , got it sparking , cleaned a the earthing points , now i have a fuel pump problem , its staying on making a contant clicking sound . ive tapped it with hammer , removed it cleaned the contacts re fitted still the same .if i have to get a new one what do i go for , there is a lot on the market .this one is made by hardi , 1979 thanks .
daz

I hope this does not sound silly but I had exactly the same problem and replaced leads, distibutor cap, spark plugs etc.

Turned out that the heater valve was imperceptibly dripping condensation (this is vertically above the distributor on a B).

A 12 pounds replacemnt valve has solved problem!
J S Lewis

Sounds like you've got fuel vapourisation.
If you open the throttle all the way, does the engine start better?
Which carburettors are you using?
Have you got a heat shield?

Mike

PS: Hardi is a German pump, made in Berlin. Didn't know they found their way to GB.
Mike Standring

Vapourisation is often mentioned but almost impossible - especially in the UK! These cars run in desert states with no problems. The only time it might happen is if the carb heat shield is faulty, you have HSs and the fuel in the jet pipes is vapourising. If it vapourises anywhere else once the float drops it will open the valve and the pump will push any vapour straight out of the float chamber vent to be replaced by liquid fuel. The heat would have to be sufficient to vapourise faster than the pump can operate, which is nearly 2 Imperial pints per minute.

It is more likely to be a rich mixture, possibly due to excessive float height, or an electrical problem like the coil.

You can only test an Ignitor in-situ or by substitution, preferably with points and a condensor, and when you find they work leave them there!
Paul Hunt

Hi , sorry to hi jack your thread Daz, I have a similar problem and was told it could be fuel Vaporisation as well, but Paul's comments re: electrical issues is interesting because I thought our problem could be related to electrics. Have you managed to solve the issue and if so, was it electrical or fuel related do you know?
Martin Clegg

A few years ago, I got stuck in a traffic jam, about 25degC, crawling along for 20 mins car started spluttering but still ran, just missing quite badly. When I got through the jam, the car ran but did not want to pick up revs. After 150 meters, it cleared up and ran fine. I put it down to fuel vapourisation (under bonnet temperature probably got quite hot due to no movement for long periods).

I remember thinking that if the car was running a little rich, after ticking over for so long, if it was possible the plugs were sooting / gumming (correct term?) up, and if after higher revs for a period, they were clearing themselves.

Anyway it never happened again but next time it happens, stop the car, check the plug condition straight away and see if they are covered and crappy, it may help diagnose!
Chris B

paul hunt

what is a faulty heat shield, and how might i correct it ? when i bought the car it did not have a heat shield, so i made one.
is there something really special in its design ?

i also have what i guess is a vaporization problem in hot weather only. after having stopped for a few minutes the car will not start and the little glass fuel filter leading to the carb is empty.
i can start again, and run just fine, after i squeeze on the fuel hose to the carb several times. this must clear things out.

john
john sutter

John,

I'm not Paul, but I don't think there is any reason you can't make your own heat shield. However, they are not just metal, they have insulation on them too. I think you can use some insulation from a home supply store that is used for protection when soldering copper plumbing near flammable walls.

Charley
C R Huff

As Charley says there should be a slab of heat insulating material on the manifold side of the metal heat shield, under each float chamber. Originally asbestos there are safer materials around now. Later heat shields were constructed entirely from insulating material, for the UK at least.

The fuel filter can be very misleading, from many comments and my own observations it is apparent that it can be anything from almost completely empty to almost completely full and have no effect on the running of the engine. Once the floats have dropped and the valves are open any vapourised fuel in the supply line will be pushed straight through the system and out of the float vents to be replaced by liquid fuel, it is only then that the floats will rise and shut off the supply i.e. cause an SU-type pump to stop chattering. That pre-supposes the fuel pump is working of course. Squeezing the hose could be co-incidental, or it could indicate the inside of the hose is rotting and causing the blockage.

If the plugs are fouling in a long idle then they would do so at any time, and not just in hot weather. Whilst HS carbs will richen slightly in summer compared to winter it's not that much, unless the mixture is over-rich to begin with. Fouled plugs could be caused by faulty ignition as much as anything else.

If you have a non-starter or can reproduce a missfire with your head under the bonnet then the first diagnosis is to clip a timing light onto the coil lead and each plug lead in turn and watch for one or more of them exhibiting no or intermittent flashing. When on plugs 1 and 4 you can also check the timing.
Paul Hunt

This thread was discussed between 12/06/2009 and 08/07/2009

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