OVER RUNNING

Running on - usually hot spots in the head, mixture combination.

Ok thanks, Too weak or too rich?

Check your ignition timing, static and dynamic. Remember to disconnect vacuum hose when setting timing.

Chris

You're right, Rob. Lean mixture can cause running-on due to hot spots. It's also possible for hot spots to develop due to over-advancing or over-retarding the ignition. Very rarely it can happen due to a cracked exhaust valve.

Cheers,

Kelley

The reason I ask is I can't get the idle speed below 1200 rpm, unless I run as lean as a very lean thing. What else could be causing it to idle at about

A vacuum leak? The throttle valve not closing properly? The breather pipes might be split, or there might be an air leak in the crankcase or your oil filler cap is letting by too much air(sounds a bit silly but the engine sucks air through this point for breathers!)

miniman

And even down to worn throttle body shaft.

Its leaned off because the air/vacuum is sucking the piston and needle up too far at idle!.

Yep its an air leak somewhere. even check the inlet manifold tightness, squirt some oil over the flange and see if that slows it down or oil/smoke comes out the exhaust.