Thanks guys,

I checked the afm with a Fluke meter and it went to about 3.8 / 4.0 volts. I haven't checked vacuum but to answer Aidan's question, no, the 02 does not go rich when you blip throttle - it switches fine at idle but is fairly weak at no load steady throttle.

The fuel pressure staying steady at full load makes me think there are no flow issues - and someones recently fitted a filter.

I'm inclined to agree with the afm suggestion but not had any experience with this type. If I scope it should I expect a similar trace to the Bosch hot wire types?

Ta
Dick