Is it the timing chain?

Hi there,
now I short to taking apart everything to have a go at the timing chain, but wanted to make sure:
She has misfire on idle. Irregularily, and it's not only one cylinder. All plugs are black, whether she's running lpg or petrol, normal or rich(dont let her run lean). Then I've had tappet noise, and some strange metal noise on decellaration. Adjusted tappets twice, they're alright. Timing is ok, too. She does have an electronic ignition, but there's the same problem if I turn it off (uses points, so just flick the switch). Now she's got half a litre ATF so I know it's not the tappets, but they look good, so do the rocker arms. When under loead there are no problems, at all. Pulls up a hill like a fully laden VW Polo (no she doesn't. In fact she's a great runner.) So problem only on idle.
Am I right suggesting it's the timing chain? Do I have to get the rad off to check it? I don't have the standard fan anymore, so I do have some space between engine and rad.

Thanks for the help,
getting desperate,
Phil

PS Will post pics of the LPG conversion lateron, did it this weekend only

If the timing chain was out you normally have worse symptoms, but I've never had that with a landy engine, however it sounds more like to me that the engine is leaning out at high throttle, that explains the metallic pinking sound, and pulling well uphill.
If it is this you'd better sort it, the engine wont stand it for long.
Check out the carby.

Loose chain or worn tensioner may result in irregular tickover but is obvious with a timing strobe - the timing mark will hunt back and forward. It's a pain to take the rad off but it really improves access. If the wing bolts aren't too rusty it might be easier to take the whole front panel off.

Never had the chain problem on a landy but had an mgb years ago with a chain... tensioner wore and there was a very distinct clattering from the casing even though it still ran... of little help I know... but have you got a rattle at the front of the engine... it was excess play in the chain causing it to catch the cover.

I had a chain tensioner sprocket break up fairly catastrophically once - I think they're aluminium alloy to keep the noise down.