Can anyone tell me where the spring goes in a os 200P regulator. I opened it up for cleaning and I am not sure which side of the diaphragm the spring goes, on the cover side or body side. The spring is also conical . I can not find any info on the web.

Message Bax in the OS section. There not going to release that kinda information to the public because OS does not want the customers disassembling it.

Just a Guess.
If it works in a similar way to a gas 4 stroke engine (i.e. Honda for example) the spring will be on the cover side with the narrow side towards the cover and wider side resting on the diaphragm.
The fuel pressure will act against the spring by pushing the diaphragm towards the opporite side (cover) and the spring will act to restrict the flow of fuel (hence the regulator affect).
I have seen many regulator diaphragms on Walbro's, Zama's and the likes but never on an OS 200P, a picture is worth a 1000 words...