James, I'm stepping out a bit here since I am not really familiar with your system. However on my 123 and 126 I don't even use the primer. I just fill the new filter up with fuel and put it back on (main filter). On pre filter, I just have the new filter ready and don't let a lot of fuel leak out of the lines when changing. I do have the backup of a primer pump, but never have to use it.

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John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln