The gasoline leak is caused by broken plastic fitting on the "crossover" vent pipe that equalizes air space on the left and right halves of the tank.  Common problem.  Repair kits are available, but you need to drop the tank to get access.

For the bucking and stalling, could be the "temp 2" sender (cheap, and easy to replace) or possibly the oxygen sensor.  With the engine off, you can disconnect the O2 sensor and see if the problem goes away.  If it does, the sensor or its wiring may be bad.

Allan

On Tue, 01 Dec 2009 13:47 -0800, "Dave Lindemann" <d_g_lindemann@YAHOO.COM> wrote:
> I am the proud new owner of a 1990 Vanagon.  The van is great but it
> takes a few minutes to warm up.  It starts right up, but there is an
> engine skip when it first starts up.  If I let it run for 3 or 4 minutes,
> the skip goes away and off I go.  If I try to drive with the skip, it is
> very difficult not to stall and the van bucks with extremes of stopping
> and going.  It looks like there is a new distributor and spark plugs and
> the van seems to have been very well maintained by the previous owner.
> The other noticable problem which may or may not be related is a gas
> leak.  When I fill the gas tank completely, there is gas leaking on the
> ground under the tank.  If I only fill the tank to about 3/4, there is no
> gas smell or gas leak.
> The skip almost seems like it could be some type of choke control.  My
> other thought is that the fuel compression is compromised by the leak in
> the tank.
> Please let me know if anyone has any ideas about this problem.
> Thanks,
> Dave