[Mgs] Advice please, bad miss

[Simon Matthews]

We have a '71 MGB GT, which is largely original (even has the smog pump).

It has recently developed a bad miss. The miss occurs under some
throttle usage: it seems to idle OK. The miss starts happening quickly
after the car is started.

My first thought was fuel starvation, but I removed the pipe from the
fuel carburettor and turned on the ignition: plenty of fuel came out.
I checked the levels in the float chambers and I think they were OK.
They were both the same and about 3/4 inch from the top. This car has
an aftermarket fuel pump mounted on the inner fender.

I also wondered about head gasket, but the miss happens even if I
prevent any pressure building up in the cooling system by removing the
radiator cap.

I have recently replaced all the plug leads, distributor cap,
condenser and plugs. I have not replaced the coil, but the fact that
it seems to idle OK suggests that ignition is not the problem.

Where should I start with this car?

Simon