Question about Welbike fuel tanks
 

Greetings Maple Leaf Up folks!

I am editing a piece about Welbikes, and as a result, have fallen down the worm hole of details. And worm hole it has been--my brain is spinning. The only thing I could think of is ask the collective brain power of the Maple Leaf Up community.

From what I can tell, there were TWO styles of fuel tanks utilized during production:

The first style seen in this period photo of Mark I Welbike, census number C4659218 and again on a restored example with census number C4659235. For a point of reference, the fuel tank vent screw is on the near side (left) fuel tank.

On the second style (seen in the third photo, brown-painted Welbike), the fuel tank vent screw has been moved to the far side (right tank) and the filler cap on the near side tank has been improved as to allow finger tightening.

NOW FOR MY QUESTION:
When did the fuel tank change? Was it at the beginning of the second contract as part of the Mk II revisions or was it done during the MK I production?

The reason I ask is that many of the restored "MK Is" that I see have this later style fuel tank arrangement. This has really confused me.

I would appreciate any clarity on fuel tanks that a Welbike expert could share.

Thanking all in advance,

John A-G
(down in Minnesota)

Were I to guess, the vent has to be on the opposite side to the filler spug.
In the first example , the filler is the plunger, and in the second example, a filler plug is added to the right tank.