[Johnny]

The St has had this a while and after the rebuild it is still there.

When I fill up the bike is transformed. As the tank gets lower the lumpiness increases. I have changed the fuel filter and cleaned the inside fuel cause. I checked the vent and cleaned that all out. Any clues?

 

[SS904]

Pump?

I think I'd do a fuel pressure check with a nearly empty tank, then fill it up and check again.

 

[bradblack]

is this in a single ride or over several?

if a single ride, ride with a spare key in the cap and crack the cap while it's playing up.

have you removed the pump from the mounting plate to see if the cavity under it to see if it is clean?

 

[Johnny]

It is every time, and for some years now. I actually replaced the pump this year when I was replacing everything to try and get the bike running

I need to maybe dismantle as much of the pump assembly as I can and clean and blow out everywhere

 

[spikey1973]

had the same issue with my ST4, never found out why.. but i had so many other issues that i kinda lumped it to that.