Intermittent cutting out/not idling

[sunbeam alpine]

The cadmobile has started misbehaving. It drives fine, no hesitation or stutter under acceleration, but occasionally, once it's warmed up, it won't idle. It doesn't stutter and stop - it just cuts out at soon as I take my foot off the throttle.

When this happens, it won't restart on the key - all the lights come on when I turn the key, but the starter does nothing. However, if I drop the clutch and bump start it, it starts and runs fine again.

It only does this intermittently. In addition, sometimes it shows the same symptoms when trying to start when warm after it has been parked for a short time - all the ignition lights come on, but nothing from the starter - no solenoid click, nothing.

I've already changed plugs/leads, without improvement. Battery is less than 6 months old.

Any suggestions most welcome.

[Seek]

Loose earth cable will give weird effects
Fault in ignition lock
Failing alternator

[sunbeam alpine]

Thanks for your reply (and sorry for the delay in replying).

Seems to be a problem with the fuel tank not venting properly - when I open the filler cap there's a rush of air. If I don't completely tighten the cap it doesn't happen. Will have to look at the vents.