fuel delivery issue...?

[Willoughby]

I`ve just returned from a 2 day jaunt to Williston from Cape Town... prior to going I took my Wee 650 into Suzuki South in CT to have the fuel filter under the tank replaced because I the bike was petering out of power (fuel) when I came off a quick road and into the the lower gears.... All seemed fine for a while but at the start of the trip it did it again... I bought a bottle of additive for the fuel to clean the fuel injection which seemed to work until I was coming back into CT 1000kms later then the same thing happened...
I am pretty sure it is dirt in the fuel tank... Any views? The bike has 118000 kms and sits for 3 weeks between rides...
Does anyone know a mechanically minded person in CT who maybe able to help me take the tank off and flush the whole system?
By the way fantastic 2 day ride, although I've got a lot to learn about sand!

 

[wave rider]

 

[Pom]

 

[WheelieDog]

 

[Wolzac]