Date: Sat, 16 Jun 2012 22:59:10 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: AFM adjustment; clockwise or anticlockwise?
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At 03:01 PM 6/16/2012, neil n wrote:
>inside the AFM. Dennis has already commented so am not suggesting one
>should adjust anything inside the AFM. But maybe someone could use the
>info to correct a PO's attempts at adjusting the Afn?
There's a very plausible method on the Samba written up by a
mechanical engineer who put some study into it, and I may even have
commented that it seemed reasonable to me. But a couple years ago
while dealing with the famous Millie's Van I had to try to do exactly
that, bring back into adjustment her AFM which had been tweaked by
some mechanic up at high altitude on the theory that it would run
better and then should be re-tweaked when it came back down. It ran
ok once you got above 2,000 rpm but it would bog down from idle and
then be feeble up until about 2k where it would catch hold. I found
it not *too* difficult to find one or more combinations of settings
that would idle ok and run ok at a fixed speed, but getting the
transient response to behave (coming off idle for example) was a
totally different story.
I finally took the still-sealed AFM off my 2.1l (this was a 1.9l) and
rigged the two AFMs in series with a throttle body and a shop
vacuum. I energized both AFMs with five volts from the same supply
and read the wiper voltage on each with separate (but well-matched)
meters. By moving the throttle plate I could vary the air flow from
very little to just about wide open and anywhere in between, and have
a stable reading on each AFM. I adjusted the 1.9l one to track with
mine, but knowing that mine was built for an engine with 10% more
displacement but otherwise similar, I adjusted Millie's to read 10%
higher at all airflows. The two tracked the percentage difference
very nicely, we stuck it back in and it worked quite reasonably and
the wiper position at idle was where it clearly had spent most of its life..
I think that's a very good way to adjust a tired one (preferably the
same type, but needs must...) or one that's been messed with to match
a known good one, the newer the better. The three basic adjustments
are wiper position on the shaft, idle plug position, and spring
tension. They interact a lot as I recall. But in an hour or so on
the bench I did what a great deal more fiddling on the vehicle
utterly failed to accomplish.
Yours,
David
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