[pettaw]

I would suspect an air leak, the best way to test this is by using WD-40 or an unlit blowlamp and wave it around all the hoses and particularly the joint between the inlet manifold and the carburettor, these gaskets can crack inside but look fine on the outside. When you find the leaky joint, the revs will rise suddenly to a much more normal idling rev.

PLEASE DO THIS IN A WELL VENTILATED AREA, because the idea is that the vacuum leak will pull in this basically flammable spray or gas that you're holding near to it and cause the combustion to suddenly enrichen.

Once you've tried that, come back and we'll try to advise you what to do and what it might cost you in terms of parts.

Andy