Re: [T3] Timing and dwell

[Simon Glen <simonglen@bigpond.com>]

Here in Australia there are currently three types of petrol
(gas) available and all are lead-free:
        90 octane unleaded
        92-96 premium unleaded
        90 octane lead replacement

The last one is supposed to be for older cars that were built for
lead in the petrol (gas).  However, older car owners who are
enthusiastic about their cars tend to stay clear of this fuel.  Instead,
they either,
use the more common 90 octane unleaded in their car but with
500ml of two-stroke oil added to every tankful of petrol  (about
50litre tank) (to give upper cylinder lubrication)
or,
use premium unleaded and adjust the timing accordingly.  This
is supposed to be the preferred option for air-cooled VW owners
because they already have hard seats etc for their valves.

One brand of premium unleaded (Shell Optimax) is only 92
octane but is supposed to have just about the best additives to
compensate for the lack of lead.  This is what I use in both my
air-cooled Volkswagens (1969 VW 411 and 1978 VW Westfalia)
and both have Type4 engines.

As a result, I do not set my timing at the marks recommended by
the VW factory.  The leaded fuels these cars were designed for no
longer exist.  After ensuring that my tappets and dwell angle are
correct, I initially set the timing statically (i.e. not with a stobe light
and running engine) but slightly more advanced than the "correct"
mark.  I then test drive the car (after warming up).  I take it to a hill
nearby and try to accellerate uphill in top gear at about 45km/h
(26 mph).  If this is fine, I stop and advance the timing just a little
more and retest the car uphill.  I continue advancing the timing and
testing until she just begins to pink and performance falls off.  Then,
I retard  the timing by 1 to 2 degrees.  This I expect is the optimum
timing for the fuel  used.  I try to stick to the same brand and octane
fuel.

I would be interested in others' views on this.

Simon Glen
Toowoomba,  Australia.

Daniel Baum wrote:

>  I will be left the with choice of 95 or 98
> octane lead-free petrol.
>
> Anyway, how should I expect the more potent petrol to affect the timing?
>
> While on the subject of petrol, does anyone have any experience with the
> additives used in leadfree fuel in old engines to simulate lead? I know the
> proper solution is to change the valves so the car can use leadfree fuel,
> but I need something I can use until I do that.

-------------------------------------------------------------------
Too much? Digest! mailto:type3-d-request@vwtype3.org Subj=subscribe