Re: [AMC-list] FSJ carb/mileage

[Frank Swygert <farna@xxxxxxx>]

Just making sure! You and Tom might be onto something with the power valve, though it runs fine at lower speeds. I think the fact that I have it rigged to open the secondaries manually at 2/3 throttle and was over that for the whole 75-80 mph run (on the floor up hills) might have been the biggest problem. I do need to look at the carb, and will do so later. I'm not real good with carbs, but have a brother and a couple racing friends who are. I don't recall what size the secondary plate is, or the PV. The person I bought the carb from said it was set up for a big six cylinder, and I changed the main jet size -- went down two sizes IIRC. May have been setup for a 300 Ford, but the secondary plate shouldn't be too far off from what a 258 would want.

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Date: Fri, 4 Jun 2010 11:56:35 -0700 (PDT)
From: Jesse<j2sax@xxxxxxxxx>

Yesiree, Frank, I read the whole thing and, once again, I found it hard to believe that your mileage fell so abysmally once the "aerodynamics" kicked in (which actually starts to happen s little over 50, but does grow rather exponentially as speed increases).? I believe such a drastic drop in mileage is being contributed to by another element.? The below suggestion to tune the carb is a great place to start.?

I have had more than one 6 cylinder FSJ and, though I don't think?I ever cruised at 80, at 75 the mileage drop was not almost 50% of my optimal.? I think something else is going on to make your 258 get as bad or worse mileage at 70-75 than any of my 360's.? Not trying to be contrary or arguementative, I just think you may be missing an opportunity to better your already cool FSJ!?? If a fuel dumping condition does exist, it could shorten the life of your rig with unnecessary oil contamination and generally gum up the works, from Valves to exhaust... even worse if you have to run a cat where you live.?

Just sayin', that's all!? Either way, hope you have a GREAT Weekend,


--
Frank Swygert
Publisher, "American Motors Cars"
Magazine (AMC)
For all AMC enthusiasts
http://www.amc-mag.com
(free download available!)

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