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Big Twin
Bikes: 959
Posts: 1,134
Join Date: Nov 2008
Location: Surrey/Northants
Do you have a spare pump you can try?.... These are similar problems to when my pump was playing up at Mallory in 2010 (on a 583, but even so). We replaced everything and wiggled every part of loom with engine running.... Eventually cured with new pump (mine had an elec pump on it). Mine would tickover fine and run fine for 5 laps... Then the gremlins would strike.
Or the tank breather?.... Run it with cap left slightly open. It is a long shot.... But just maybe enough of a vacuum could be formed to overpower the pump?
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