What Charles said, run an aux. filter with your "newer" style system. The sintered bronze or paper filter in the carb will never get fouled up. You do not want to be replacing the in-carb filter on a q jet much, if at all. I don't know which system is "better"....I've heard the earlier one was due to the extra capacity and cooling of the large additional fuel filter, but the second system with the add on filter would/should be just as effective. I think it was a cost saving issue: the second design uses less plumbing and parts, plus less labor. It's a cleaner looking design, too, without all that stuff jammed up around the T-stat.
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Jeff 
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