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Re: [T3] '68 SQ w/ dual carbs questions

On 10 Dec 2002 at 17:21, Steven Ayres wrote:

> JimA=> The vac adv/mech adv dists only use the vac advance to
> => give extra advance under light load at high speeds.
> That's clearly how it works with FI, but with (stock) carbs the vacuum
> advance on this distributor has more and different function (I'm driving
> it). I agree that manifold vacuum wouldn't work. I'd recommend the
> questioner check advance with an advance-equipped timing strobe during the
> tune-up procedure to determine what's going on in there, both at low and
> high rpm.

The stock dist and carb setup is different from what he has. He has the 68 FI 
dist which has all the advance he needs in the mechanical part. I believe that 
all the stock dists (is that what you're using?) have vac advance only. If you 
try to augment the mechanical advance with extra vac advance I think you're 
risking having too much advance under some circumstances.

It's not that you can't do this, it's just that i don't think it's a good idea. 
More advance may be better at times, but too much can definitely be hard on an 

I certainly agree that if your dist only has a vacuum advance, then that's the 
only advance that you've got and it has to be working right to get normal 
engine performance.

It was my understanding from talking to Dave Hall in the UK that the later 
versions of the dual carb type 3 engine, like the FI engineso of the same era, 
also came with mech/vac adv dists, and that they worked exectly the same way as 
the FI dists. That is, that the vacuum portion only came into play while 
crusing, not under load, and was also just a fuel economy device.  

I probably don't understand what you mean, so please explain exactly what you 
are running.
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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