Can't say what is causing it but I can sympathise with you, my 87 Syncro does the same thing.  Cold start in wet weather(usually after having been driven wet weather) loses power until I shut it off and restart it, will do it for the first few stops then clears up and is fine.  Also happens if it is driven in a heavy rain for a while.  I have yet to try and diagnose mine but will definitely watch the replies to your post and add the repair to my ever growing list of things to do before the snows come.

Mark in AK

----- Original Message -----
From: Richard Golen <rgolen@UMASSD.EDU>
Date: Wednesday, October 10, 2007 10:55 am
Subject: Power loss when engine wet and cold
To: vanagon@GERRY.VANAGON.COM

> Hi,
>
>
> My 87 Westy has a power loss problem. It occurs when the engine is
> cold and the engine is damp (from recent rain or high humidity), and
> lasts (usually) for about 10 minutes. As I accelerate (partial or
> full throttle no difference) the engine bogs and looses power. If I
> shut the ignition and turn it back on, the problem clears....and then
> comes back until I've driven for 5 to 10 minutes. It also happens
> when the engine is warm and I'm driving through heavy rain.
>
> Anyone know what the problem might be, and what can be done to fix it?
>
>
> Thanks.
>
> Ric
>