Re: [AMC-list] Jeep mods/mileage

[tom jennings <tomj@xxxxxxx>]

On Fri, Jun 4, 2010 at 4:41 AM, Frank Swygert <farna@xxxxxxx> wrote:

>
> As long as I stay at or under that 65 mph threshold where wind resistance
> starts to really take a toll the truck gets 17-18 mpg. Only when pushing it
> and "standing in the four barrel" does gas mileage plummet. I have a vac
> secondary carb, but I've got it rigged so that the secondaries open at about
> 2/3 throttle whether there's enoug h vacuum to pull them open or not. The
> engine has over 100K on it and I don't think it produces enough vacuum
> sometimes to pull the secondaries open. I may have had them open on that
> high speed run more than needed.
>

17, 18 sounds about right, but as you increase MPH/increase wind load etc,
the mileage shouldn't plummet, just worsen.

This is a very fine-grained suggestion, as it sounds like you have it close
to right, but drive with a vacuum gauge in the cab, run to 75mph steady, o
rwhatever you'd like to cruise at, and see what the reading is. Then pull
the power valve from the carb, and make sure it's rating is lower than that!
If your cruise vacuum drops below the P.V. rating it opens and dumps a
crapload of fuel.

The vacuum secondaries are opened by a spring, and closed by vacuum, I think
you just misspoke there.
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