Check this great site:

http://www.applianceaid.com/gas.htm



wrote:
Can all cook stoves use both propane and natural gas?

When I moved to the country a few years ago, I had to adapt to propane
for gas. I had an older kitchen cooking stove that was set to use
natural gas and all I had to do to convert it to propane was adjust
the orfices to make the openings smaller. Similar to the needle
valves on carburetors.

I need a new (used) stove. Natural gas stoves are easy to find, but
not propane ones. I am asking if all of them can be converted by
simply turning the orfices or do some need replacement parts, and/or
are some not able to be converted at all? I dont want to buy one and
not be able to use it.

Does anyone know for sure? Which brands if some can and other can't?

Thanks