Minor Occasional Misfire

Every now and then the engine misfires a little, even when steady motorway cruising. There appears to be no particular situation that it happens, pure random?

The engine is running a little rich at the moment (11.5ish on boost) and maybe contributing to caked up spark plugs? (haven't physically checked them)

Also wondering if it could be any of the following:

-TDC Timing Sensor

-AEI (diaphragm split)

-Poor power feed to AEI (as per Ian S's "Click, click, click, vroom addendum)

Another symptom during the misfire is the tacho needle going crazy, which makes me think electrical/ignition?

check the tdc wire that it hasnt melted etc... and that the sensor its self is ok

TDC Sensor is in good nick and appears to be doing the job. I check the spark plugs next as I remember Brigsy saying new plugs cleared up a misfire that he had on his Extra Van?

NGK or Champion plugs of the correct variety are not sold in Oz, so i'll have to go with the eBay UK option or similar?

Also did the Ian S addendum mod and made no difference.

check/replace the engine block earth lead.

Check the lead from the flywheel sensor where it goes through the bulkhead, it can
wear and short out.

fit a new relay on the overboost circuit.

Russell, the addendum mod replaces the over boost circuit.

My AEI is the engine side of the bulkhead (phase 1.5?) so doesn't pass through a bulkhead.

I'll check out the engine earth strap and maybe chuck on an extra one for good measure.

also check the dizzy and ht leads

If shes rich on cruise chances are the plugs may be fouled up, whip them out and see:)