Thankyou for your help so far I'll take a look and report back after Christmas. I think you're on the right lines here so you've definitely pointed me in the right direction. The double handed switch etc I'm replacing has 2 springs so maybe mine is missing one for starters and it has a slightly different set up but essentially does what you describe. May be worth buying another 2nd hand unit and keeping my fingers crossed.!

Thanks I appreciate your help on this . I've had another look and bent the spring nice and flat but it still works it s way off the trigger once you put everything back together. It's basically laying on top of the on off switch which seems kinda weird to me also.

In position

This shows the trigger back in position but without the spring underneath tensioned in any way beneath
Stihl seem to make very neat machines the wires and cables are routed nicely and the handle clamps are brilliant.  I must be overlooking something here with the trigger and spring surely !
If i buy another 2nd hand one chances are the spring will be detached once the handle is separated so probably wouldn't be any better off. Hope pictures are clear and I look forward to any replies . Thanks

This photo shows the trigger removed and position of spring in the handle ...

I seem to have messed this up a little so may need to do each pic individually.  Sorry to make this long winded.
The orange throttle trigger is pictured with the side that faces down . Once the peg is located in the handle hole it's pretty tight against the spring and switch. I highlighted In red a 2mm raised piece moulded into the switch . Maybe the spring sits against this but there was no sign of wear and the spring in this position will move about a bit with the constant back and forth with the trigger. I can't see anywhere else obvious for it to locate tho

Thanks . I'll add some photos now and see how they look.

Hi  latest problem! Hoping someone has some knowledge on stihl throttle trigger springs. I've changed from double handle to single and the second hand throttle had the return spring unattached and I can't see where it connects to the orange trigger piece. The spring lays flat over the on off switch and is secured in place with about an inch of straight tail. If anyone's dismantled one it's probably straight forward but parts diagrams don't show how they all connect unfortunately. Not sure if I can attach photos that may help?

Hi. I picked up a little 18r strimmer from the local dump as I needed a spare tank cap and several bits looked like they'll fit my 125 (switches etc). No spark as obviously had to have a fiddle with it but also distinct lack of parts available it seems even cheap copies on e bay. Does anyone know if this shared parts like the coil with other models where I can then May be pick one up ? Thanks Martin

I think you're probably right . I shall have to dismantle what I have ( tank wooden blocks steel strips etc !) And see what fits . I can't work out why it's been modified as it is unless it's a different tank and it's been made to fit . Guess I could leave it as it is but I like them to be pretty original. I think it's over 30 years old but it's really light and has loads of compression so worth a go . Thans

Thankyou for your help. I reckon I'll need to buy a donor machine and swap the parts . Tanks are pretty rare seconhand it seems and the diagrams I've looked at don't show the brackets etc. I'm sure one will turn up tho I'll keep looking.

Hi. I've recently purchased an old fs66 and would like some advice regarding the fuel tank. I need a good photo to determine if I've the right tank and how the tank is fitted. Mine is Not get with a block of wood and tin. It would be nice to put it back to original when I can source a good second hand part. Although the tanks appear dis continued I'm wondering if a few brackets are still out there. Also may be other models shared the same tank? Any help would be appreciated.  Many thanks