I hope my attempt to help doesn’t just muddy the waters….
You will indeed need a Shock Pump. The Marzocchi valve adaptor is also required in order to get air into one or more of the Schrader Valves.
The manual that I have seen on the Marzocchi site is very confusing – as was the manual for my version. Have a look at this with that in mind;
http://www.marzocchi.com/template/detai ... etto=2434#
If you scroll down to 5.2, there is a poorly written explanation of how to adjust the Negative pressure. I reckon the Left & Right legs are incorrectly referred to in this manual – but onwards.
The Negative Air chamber is smaller then the two Positive chambers, and ramps up quickly at the end of the rebound (extended / at rest) stroke. As you increase the pressure in this negative chamber, it pushes the fork into starting its Compression stroke. This results in the forks sitting lower at rest, or reducing the travel & A-C measurement.
Incidentally, Rock Shox Dual Air set-up, do indeed have a spacer fitted internally to achieve a change of travel & A-C measurement. If I am correct with my assumption, the Marzocchi Marathon SL doesn’t use this method.
Anyway, the Negative Air chamber Schrader valve on your forks should be positioned in the centre of the Top Cap, rather than over to one side. I reckon this is sitting in the Left leg (as viewed from sitting on the bike). The manual, IMO does confuse matters.
See what you reckon HB – let me know if you need me to waffle on some more! We should get this sorted however when you get hold of a pump and adaptor.
1989: Kona Cinder Cone | 1993: Kona Kilauea | 1996: Kona Ku | 1997: Kona King Kahuna Stars ‘n’ Bars 18” Vs - Kona King Kahuna 19” Disc - Kona Explosif - Kona Koa | 1998: Kona Hei Hei - Kona Ku | 2000: Kona Explosif - Kona Kula | 2003: Kona Kula Primo | 2007: Scapin Kyoto | 2010: Kona Kilauea.