Gas Milage Award?

[jlandry@domain.elided (John A. Landry)]

Hey everyone,

I think I may qualify for the "Worst Gas Milage on a Trip" award!  More
details on that in a second.

I just got back from my hunting trip in NE Washington state pulling my 18
foot twin axle travel trailer with my 76 Traveler.  Luckily we encountered
no snow or ice... only lots of rain and mud.  The trip had many steep up
and down grades and driving on rugged mountainous logging roads.

On the way out early Saturday morning, I stopped at a WA State Patrol
commercial vehicle weigh station and asked the nice officer if he would
weigh my Traveler and trailer.  He was more than happy to... as he ate his
pastry.  The results were as follows:

Front Traveler axle = 2700 pounds
Rear Traveler axle  = 3080 pounds
Trailer axles comb. = 3780 pounds

Total               = 9480 pounds

At the NW Binder Roundup last August, I recall John Hofstetter guessed my
trailer weighed maybe 3400 pounds just by eye balling it, so he was really
close.

The Traveler was able to climb all but the steepest grades at 60 mph, which
was the speed I cruised at even on highways posted faster.  It has a V345A,
Edelbrock 1404 carburetor, a TF727 automatic transmission, 3.54 axles and
10.5 x 31-R15 radial mud tires.  The really tough grades required driving
with the four barrel carb wide open *or* at about 40 mph in 2nd gear at
part throttle.  Along the way, as I watched the air / fuel mixture gauge, I
realized that my carb jetting wasn't set up properly for pulling a heavy
trailer.  The mixture was too lean (under part throttle acceleration) to
allow the engine to develop enough power for freeway cruising.  This caused
the carburetor to be operated much like it was under heavy acceleration
(a.k.a. "power mode") all of the time.  The result was and overly rich
mixture and heavy fuel consumption.

My carburetor is normally operated at or near sea level, so it's adjusted
to suit that condition.  At the hunting area, the altitudes ranged from a
low of 2500 feet to more typically 4000+ feet.  This caused the air / fuel
mixture to be slightly richer than needed and again... excessive fuel
consumption.  Then to top it off, I did a *lot* of driving in 4L while in
the hunting area.

After figuring out what was going on, the last half of the return trip I
changed the carburetor jetting to give a slightly richer cruise mixture,
while at the same time I delayed the activation of the power mode until the
engine vacuum dropped to 3" of Hg (throttle almost wide open).  This seemed
to help a lot with more power and allowed slightly better fuel economy.

Normally I average about 13.5 mpg in highway / city driving without the
trailer.  On this trip, the gas mileage varied from a low of 5.453 mpg
(without the trailer after spending a day cruising logging roads in 4L)...
to a high of 9.313 mpg (with the trailer after changing the carb jetting on
the return trip).  Remember, this was pulling a loaded trailer up *long*
steep grades over mountain passes, so even tho the number is pretty bad,
it's understandable.  On the trip out, the gas milage averaged 7.352 mpg.
On the return trip, the gas milage averaged 8.336 mpg with a consistent
head wind.  As you can see, the jetting changes made a significant
improvement (13.4% increase).

The good thing is that the Traveler handles great pulling the trailer, no
matter what the road conditions were.  On the way into the hunting area, we
got lost in the dark (another story altogether) on a rutted logging road
over a mountain pass, and the twin axle trailer was well behaved... even
with all the swerving and dodging to avoid the pot holes.  BTW, I have no
sway bar or equalizer hitch, so I'm amazed how well the trailer pulls.

So, for those Digest members who mentioned they've experienced 8 or 9 mpg
pulling a trailer with their IH vehicle... I think I might have you beat!

Oh... and Bambi's dad is safe in the woods (at least from me) for another
year. <grin>  It was a great trip anyway... lots of tall tales, bonding and
beer around the roaring campfire.

Take care,

John
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