If you need to conduct fixes to your Derbi Boulevard 125 then it is usually recommended to possess a Workshop Manual to use as reference in case that you need to know easy methods to take out a particular component for instance the Drive Shaft and install it again properly.
Derbi Boulevard 125 Workshop Manuals provides identifiable diagnostic info with regards to your car therefore if something is not working it can help you figure out what the situation is and the way to fix it. You will be able to assess if this can be done by yourself or if ever the job is too big it is possible to book your Boulevard 125 into a nearby mechanic.
Derbi Boulevard 125 manual