Date: Thu, 26 Sep 1996 22:52:09 -0700
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: ddes@anet-dfw.com (David Schwarze)
Subject: Back from Mammoth, carb thoughts (long)
Yep, Unca Joel and I made it back from Mammoth in one piece, but with a few
more grey hairs than before. It was definately worth the drive, but I
wouldn't have made it without unca Joel's help. I think we all had a great
time - I think it was the best CCC campout yet! Attendance was terriffic
and there were a few new faces as usual. Thought I'd share some stats
about our trip:
Miles out: 1550
Time to drive out: 34 hours (2 dinner stops + Las Vegas gambling stop)
Miles back 1743 (Suthhhun rowte)
Time to drive back: 57 hours (2 overnight stops + a few dinner stops)
Total miles driven: 3293
Gas consumed: About 168 gallons
Average speed: About 60 mph @ 3900 RPM
Average mpg: 19.57
This was only from my house in Dallas - Unca Joel got to drive another 10
hours EACH WAY! And I thought I had stamina...
I was very pleased with the MPG, especially in light of the fact that we
climbed to over 7,000 ft. elevation and back down to near sea level at
least twice during the trip, and ran at nearly full throttle for about six
hours trying to make it to Phoenix on the way back.
Before we left, I swapped jets in my carbs. Since at least one person has
expressed interest in carb jetting on dual Solex'd engines, I thought I
would share my experiences. FI dorks might want to hit "d" now. :-) No
really, FI people aren't dorks, I'd be one misself if I could. Except for
Steve Johnson, now he's a dork! Hi Steve! Did your bus make it home? :-P
Since the rebuild, I have run the carbs with 137.5 main jets and 175 air
correction jets. These are the largest jets of both types that I have. I
figured with 200cc's of extra displacement I could probably use it, and too
much is better than too little. Ran that way until the start of the trip,
or from mileage 0 to 13,000 on the engine.
With these jets, the engine ran well and accelerated smoothly at near sea
level, but mileage was not impressive. On a recent trip to Busses by the
Arch I averaged 16.99 mpg over 1,139 miles of almost all freeway driving.
I figured I would swap in smaller jets for the Mammoth trip in hopes of
improving mileage and to offset the effects of the higher elevations we
were going to encounter. Happily, both hopes came true. The range of
available main jet sizes (AFAIK) is 127.5 to 137.5 in 2.5 increments - I
put in 130's. The air correction jets are available from 140 to 175
(AFAIK) and I chose 155 for no particular reason (since I really don't know
what the air correction jets do... can someone enlighten me?). With the
new jets in, mileage picked up noticably. On one tank we got 21.4 mpg,
which is an alltime best for my 4500lb, highroof camper. The bus also ran
great at 8,000 feet, starting easily and idling smoothly where some others
were not so lucky. On the downside, at lower elevations the engine tended
to buck a little during acceleration, and power might be off a little, tho
it is hard to tell.
The SCARY thing is that with the smaller jets, my CHT went up - A LOT.
Maybe 30-40 degrees on average. More when pulling hills. Before, with the
larger jets, it would always stay near 250, going up to 275 when pulling
hills. Now
it stays around 275 all the time, and pulling hills we saw temps
approaching 350. This is at the temp sender boss, not at the spark plug.
Spark plug temp readings would undoubtedly have been 100 degrees or more
higher. This made me very nervous, but not nervous enough to stop and swap
jets.
I am sure it's a result of the engine running leaner, but is it running too
lean? I'm not sure. I'm hoping that a change in the air correction jets
(smaller or larger? I'm gonna try both) will help, but if not I'm going to
try 132.5 mains (Dave Kautz, this is what you run, right?) to try and lower
the CHT readings. If that doesn't help, I'll run the small jets for a
while and then pull the heads and inspect them for signs of overheating
(cracks). Now that I've had a taste of good mileage it's hard to give up,
but I don't want to burn up my cylinder heads. Oh, oil temps show no
noticable change before and after the jet swap. Within acceptable range
the whole trip.
Well that's all, as usual comments, flames, etc. are welcomed. Have a good
Friday, everyone...
-David
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David Schwarze '73 VW Safare Custom Camper (Da Boat)
Dallas, Texas, USA '73 Capri GT 2800 (Da Beast)
e-mail: ddes@anet-dfw.com '87 Mustang Lx 5.0 (13.986@100.81)
or: des@eskimo.com '93 Weber WG-50 (Da Piano)
http://www.anet-dfw.com/~ddes '95, '96, '96 cats (Aackkk! Phhttt!)
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