Ok, I solved by myself.I found on the personal page of the author the lastet version of the patch who fixes the problem of insufficient memory when you don't have anything resident in high memory.So I attach here both archives: 'motos_new.zip' is the new patch (if you want to extract the files by yourself) while motos_HDD is the game already installed, all you have to do is extract the archive in your 68000 HDD (real or under emulation) and launch the file !Start.bat.
Tested succesfully on XM6 emulator and a X68000 CompactXVI, it works also on 2MB machines.
Enjoy!
P.S.
This is the personal page:
http://homepage2.nifty.com/beam-igarashi/