My throttle stays open when i pin in it back. Cables are new and lubed and routed correctly but it just won't snap back closed when i let go of it.

Is there some mod i can do to make it close better, like an additional spring or something?

I don't mind it but not sure it will pass an MOT like this.

When mine was like this I sorted it with the adjuster at the handlebar end.

What do you mean?
Put more tension on the return cable on the handlebar end?

check your twist grip tube (where your hand goes)is not stopping in from returning or the bar end weight is not binding

A modification isn't necessary if it's working properly.

This indicates a fault somewhere.

Diagnose it!

First off.. disconnect the throttle cabes from the carbs... can you turn the butterflys at the carb fully open and do they spring back ok?

This elimates your carbs.

Now remove the throttle cabels from the twist grip and pull them by hand.. do they spring back? If not then it's a cable / routing problem.

If they do then it's a twist-grip issue.

Perhaps the grip is catching on something? Is it all clean and lubricated?

I've seen it a few times on bike, usually down to knackered cables or twist grip problems but as you said yours are new then it's likely to be the twist grip

Definitive checklist; in order of difficulty to check:
Is grip binding on bar end or throttle housing?
Is bar corroded or dirty under twistgrip?
Are cables adjusted too tight?
Are cables stiff, damaged, or pinched?
Are carbs damaged, missing a part , or corroded?

It will be one of those.

Dec also check that your handle/clipon isnt bent, its not rare for them to seize after a bar warps/bends thus causing it to stay open,

Sligeach wrote:My throttle stays open when i pin in it back. Cables are new and lubed and routed correctly but it just won't snap back closed when i let go of it.

If this has occurred after fitting new cables make sure they are not crossed over and there is sufficient free play at the grip.

amorti wrote: Are cables adjusted too tight?

Spot on. Karma to you bro. Checked but the other bits and then let the tension of the top cable - the easier one to get at with the cabs still attached and as soon as i put some slack it in it was instantly cured.

Lubed the clip-on for good measure but it is working spot on now.