I am in the process of putting my sherpa back together. I have fitted the fuel tank (aluminium) with the long mounting bolt through the front, but am a bit lost at the back of the tank.

Is it just the seat that holds these tanks in place? Or is there a strap of some sort that holds it? 

Thanks in advance 

If you fit a foam piece around the top frame tube to support the tank it assists holding the tank in place but the main rear attachment is the front end of the seat

Be careful with the long front bolt, if its rubbing / tight to mount, it will wear the tank causing leaking.

1 hour ago, b40rt said:

Be careful with the long front bolt, if its rubbing / tight to mount, it will wear the tank causing leaking.

Yes very important, thus there are special rubbers for the bolt with angeled surfaces to follow the tank distributed from Bultaco, you should get them through InMotion or other Bultaco spare parts distributer.

Ok people thanks for the advice. The tank has the proper grommets with sleeves fitted to prevent the issue with the front bolt. 

Here it is at the moment ?