MGB Backfiring

[Paigemad]

The car is running brilliantly for about 10 miles and then starts to backfire very badly and loses all power and grinds to a halt. The coil feels very hot when it stops - have changed it -still the same. When the car cools down again it will go for another 10 miles or so. I was towed home by a JCB the other day ( I am still trying to see the funny side of that ! ).
Any ideas ?

[alavahalf]

My first thought was check the timing ... but have a look at what the enthusiasts say.
http://www.mgexperien...and_backfiring/108236

We all seem to have forgot about about plugs, points, condensers and gaps.
Good luck.!

[Buenchico]

Let's start with the obvious:
Have you checked the timing?

[mjwman]

For my money it is the condenser inside the distributor. Cooling down would get it going for a bit. Either that or the coil itself.
I suggest you ditch the points and get an electronic ignition . My Spitty has a Pertronix and Flame thrower coil and since fitting has not missed a beat. No more pinking, no more points or adjustments and no more timing adjustments.

[AlBags]

or find a Lumenition kit and have it fitted.
I suppose it 'could' be a plug lead or plug too. Intermittent spark and excess fuel = backfire.

[Paigemad]

Thanks for all your answers.
It now has optronic electronic ignition but the same problem.

[AlBags]

Is it backfiring .. or spitting back?
Were the leads/rotor cap checked?

[Paigemad]

New rotor arm fitted with electronic ignition and all leads etc checked.

[Paigemad]

Sorry - meant to add that it is definitely backfiring, but only when it warms up. Then it dies.

[AlBags]

Are pistons in carburettors working and damped ok?
Take out dashpot rods and check pistons/slide to make sure moving freely (if Solex)
Compression check. Is this running an unleaded cyl head conversion? eg .. valve seats done?

[mjwman]

OK try this. Have you fitted a normal sports coil which is 12v, or is it a 6v coil for ballasted ignition. My Spiity has a ballasted lead to the coil which gives a high voltage to start then when key is released reverts to 6v.
I have by passed this lead for my Flamethrower coil.

[Paigemad]

It has an MS4 High Energy coil with ballast resistor - it was recommended to be used with Optronic ignition. It is 12v though not 6v .