Ok, a friend has a 1960's bus fitted with a tuned 1700cc motor with dual down draught carbs, ignition is still points.
Issues.... Number 3 is not contributing at all, number 4 seems to contribute less than 1 and 2 but much more than 3
Compression, all within 10%
Ignition, all plugs firing
Fuel, all seems fine
Timing, spot on (IR at least as near as possible with a non vacuum advanced distributor at idle)
Plugs, leads, points, condenser, coil. Carbs rebuilt. Distributor replaced. Valve clearances checked. Oil changed. Fuel tank cleaned out and also new filters fitted.
When idling you can hear a slight miss but it runs fine and drives well, Rev it slightly seems to go away. But once running for a while the miss becomes very much more evident and the van almost cuts out. This happens faster if put under more load by towing caravan.
I've not yet had a scope on it to get any images of spark etc
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