Erratic running at full revs?

[Ian Williams]

I would suggest it is not fuel related at all, most likely to be a worn distributor or end float in the dynamo....or both!

[Dave Wortley]

My SU pump was only getting 5v when it was wired through the ignition switch. Diverted the wire through a modern switch under the dash with a warning light on the dash. Now get 6v plus at pump.

[Chris KC]

Valve bounce?

[Dennis Nicholas]

Due to the use of ethanol in some modern petrol one needs to use the rubber fuel pipe SAE J30R9.
Ordinary or lesser specification rubber gets rotted inside and collapses/gives off little bits.

Problem could be due to corrosion/dirt in petrol tank partly blocking outlet then dropping out of the outlet as demand falls off.........has tank previously been "lined" with an older "tank seal" that is now peeling off with the modern petrol?

Dennis

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Just a vague thought....I seem to remember that one of the in/out ports on the SU pump is stamped with the position where it should be placed .......yours looks to be mounted so that both inlet and outlet are equally spaced either side of the top.........may be nothing but we need every little efficiency for our motors!

Dennis

[Duncan Logan]

Give the carby a service to eliminate it as the cause if its been a while.
Could be the float chamber not filling fast enough but doesn't seem consistent with  my experiences.
Is the jet clear and the needle in good condition?
Is the pump operating smoothly at full revs?

Is the problem at full revs under load or free rev?

if you eliminate all the possible fuel issues then venture into the land of spark.