Zeph11 choke return spring

Since rebuilding my carbs a while ago I have had this minor issue. The choke wants to turn itself off. These are Keihin 34mm CVK's. The return spring is mounted on the slider plate (correct location as far as I'm aware) and the other end is looped over carb no.2's vacuum nipple. I can't see anywhere else it could go. It has too much spring tension and the choke control on the handlebar doesn't stay where you want it.
Any ideas?
Cheers

I own a '91 Zeph 750.    In my case this was the  problem; when the 'choke' (enrichener) lever did not want to stay put. ......   The friction pad behind lever in grip switch box had desintegrated. 

..The purpose of the friction pad is to resist the return spring tension of the enrichening plungers, at the carbs slider.  ..The thing is, as these bikes are getting now really old, the friction pad tends to come apart with age, and thus its effect vs the closing spring diminishes, or disappears.

The bad news is the friction pad was never sold as separate part,..either, you get the whole grip switch box or nothing.   New ones are probably un-obtainable by now, and used one (ebay, junk yards), may be in same condition (or about) as yours.

I opened up grip switch box, and built my own pad from an old "ergonomic" toothbrush handle.  The hard rubbery ones.   I used a Dremel rotary tool with grinding stone to shape it.    ..I also had to drill a tiny little socket for the little bitty spring with keeps pressure against lever.  .

If this helps,......  Just by opening box, will allow to see if this is the problem. 

According to photos of similar carbs on eBay, the return spring does indeed loop over the carb nipple. 

Thanks both. That makes complete sense Hugo. I may just 'make' the spring weaker, or take it off and see if the slider returns from the handlebar control. I'll re post results. Cheers

I think without a spring you will get the same symptoms as leaking plungers ?