At the gas station the longer vent tube would show pressure difference and make it shut off at 15. I gather after mod you need to be careful to not spray gas when close to full.
They were all actually 20. The longer vent tube in some gave a 15 option.why anyone would want it, idunno. I'll. Find the link .I know it was on youtube.
I just watched a video on how to make 15 gallon a 20. I'm going to do it. Might give you more options and the mod is free. Looks fairly easy but I got two left thumbs
