In a message dated 98-03-26 14:04:14 EST, JWALKER@UA1VM.UA.EDU writes:

<< I own and operate a company in Costa Rica called Siesta Campers
 (http://www.edenia.com/campers).  We have 3 aircooled gasoline 1981 Vanagon
model Westfalias that all are running too lean (and therefor too hot),  and
none of our repair manuals tell us how to properly adjust the mixture... ...
 Gary Nash >>

Snr. Nash,

Assuming your Costa Rican Vans are fuel injected, there is no legitimate way
to "set the mixture".

In a fuel injected system, many sensors around the engine send data to a
computer. This computer tells the injectors to squirt a little or squirt a lot
of fuel, depending on the conditions the sensors percive.

If the mixture is incorrect, it is usually symptomatic of a problem with one
of the physical parts of the system, not simply an adjustment. However, your
situation is unique. You have three identical vehicles displaying the exact
same symptoms at the same time. These vehicles may have endured an identical
circumstance that created these symptoms. e.g.

1. They all went to the same mechanic, who set the timing wrong, or messed
with a vacuume hose or wiring, and didn't put it back correctly. (But three
times?)
2. They all use the same brand of fuel, which has clogged the injectors
(partially).
3. Something else that my puny mind can't think of.

Try these things:

Run a bottle or two of good quality Fuel injector cleaner through the gasoline
tank. I reccomend Chevron Techron, if it is available there. I use it with a
half a tank of gas if I think the injectors are really cruddy.

Make sure the timing is correct. This could cause an improper signal.

Have your repair shop check the fuel pressure. Your regulator could be bad, or
the vacuume hose could be misrouted.

Open your air-cleaner hosing and check the Airflow meter. It may be stuck or
gunked up. I've never seen this, but I think someone on our newsgroup recently
reported it happening to them.

best of luck, (buen suerte)

gmbulley
cary, nc