No Speed limits in Sub

Hello,
I live in an older subdivision in Michigan and we have NO speed limits in our sub. We were told that it was due to the fact that the properties are zoned "Agricultural/Recreational Usage" and therefore exempt from speed limits. We have 25MPH limt signs posted but many choose to do 40+ MPH on narrow curving roads with no fear of tickets, even the police who occasionally cruise through will say they can do nothing about the speeders.
NOW, does anyone in Michigan have a clue where we could start to try and get speed limits posted and enforced, as the BOD refuses to do anything seeing as how they are the biggest offenders, and it would require more work than one or two phone calls.....

Thank you! We will give that route a try....

The 25MPH signs were put up in the 80's by one of the old board members who said he purchased them from the county. He put them up right after the roads were paved. Before the roads were paved, going any faster than 20 MPH in here would have torn your car apart.
And the thing is, our roads are not private roads, but county roads maintained by the county.

Well, the roads are not main roads, we are off of 3 main roads, and our roads are maintained by the county....when this sub was laid out the plan was for say, 2000+ homes, but the original developers went bust early on and later due to poor management only about half the lots were built on, and many owners bought additional adjoining lots over the years so they would not have neighbors....That is what confuses me, as there are areas around here that have fewer homes yet have a 30 or under MPH speed limit......We have been told that we cannot get speed limits as we are zoned Argicultural recreational, and we are surrounded by State land and private farms