DG cuts out over 40mph

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Hi All
I am trying to diagnose a new issue. Got the van running nicely and then sent the carb to browser.to be cleaned, took the opportunity to flush out the tank too.
Recorded everything and took the van the John galley to be set up. It runs beautifully all day up to 30mph, beyond that it will cough and backfire, then cut out.
I am thinking it's fuel starved, would y'all agree? Is my filter too fine, or my fuel pump giving up? Or the rubber Washer in the filler cap too efficient???
Opinions please?

[Mocki]

It won’t be the filler cap seal , because there are plenty of breathers on the tank . Unless they are sealed or blocked ?

fuel pump sounds a likely suspect , although I’m not sure your symptoms fit to fuel starvation as you describe them 

as you say the cab has been cleaned and refurbed , it’s unleikly to the the cone filter in the inlet spigot , and if it were the main filter down by the tank it would inhibit it at all revs ??.

I think in would be looking at rotor arm and dissy , the backfire says spark problem 

[aknapper]

check that the wee filter in the carb itself isn't blocked after all that work?
 

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This turned out to be a small flap had formed in a rubber hoses when the PO had pushed in the hard line, it eventually got weak enough that it closed the fuel off at full flow. New lines all round and problem solved