[T3] '72 FI won't idle down

[Keith Park]

Well yes, a whole pack of new variables and yes I did start with a stock 2L
914 system ( thanks to bad ebay and other ad's all was had reasonably over
time) but first gone was the IAD as that didn’t fit,
Long long story short I worked out all the issues and custom tuned the 037
pressure sensor for the vacuum sig of the 2056 and only have a few minor
details to work out, and the devil is in these details as getting that
 Mixture curve just right with what I can do involves getting inventive at
times.  Only lose about 1MPG of highway milage for doubling the HP and
torque has it pretty well tuned, but everything has to be right,

I had a bounce dryer sheet stuck in the fan last year and it ran 15 degree's
hotter, had to find that before the weather got warm but I did....  gotta be
more careful when the engine is out all winter.
Also, if you have the rear deck open to haul stuff, it runs5-7 degree's
hotter as it disturbs the airflow that much, so making that hp makes more
heat and Im at the limit of being able to dissipate that, without more
Inventive ideas that im still working on....

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.topnotchresto.com
71 Squareback  “Hothe”
65 Notchback  “El Baja Rojo”
93 RX7  “Redstur”
13 Subaru Outback "Blendin"

-----Original Message-----
From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
Behalf Of Jim Adney
Sent: Sunday, June 14, 2026 12:34 PM
To: type3 at vwtype3.org
Subject: Re: [T3] '72 FI won't idle down

On 13 Jun 2026 at 22:36, Keith Park wrote:

> Well it does run lean when warm with the AAR Open, used to see it when 
> I had the AFR meter on it and it tends to miss then too, we'll see 
> what happens when I close that off when the engine is hot.

Keith, you've added so many extra variables to an already crowded variable
space, that it's impossible to guess what your problems might be. Have you
considered trying to find a 914/4 2.0 L brain and pressure sensor to make a
more self-compatible system? That's likely to be expensive, unless you get
lucky, but it would probably get you to a better starting spot.

In the past, my own back-of-envelop thinking has suggested increasing the
fuel pressure in proportion to the increase in displacement. That suggests
that running lean would be a natural consequence of trying to simply
increase the displacement.  

Then you'd be left with the question of what difference does it make when
you substitute a different size throttle throat than the 914/4 one. I assume
it's different. Off hand, I don't think it should make a difference, since,
once again, the pressure sensor only responds to the pressure in the IAD,
which is what is feeding the cylnder. OTOH, there's probably a difference in
the pressure drops across Type 3 and Type 4 air runners, intake passages,
and valves. There's a LOT to worry about.

--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
*******************************

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