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Did you replace the rubber caps on the vacuum ports on the top of the carbs ?
You have a vacuum leak for sure... that's why the idle is high and the throttle is slow tomc one back down when you rev it... the rubber pieces where the carbs mount to may have a crack in them... take them off and check them carefully... if you push the carbs in too far when you mount the carbs to the rubber piece they will not seal properly..
 

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Very good point.
726346


@ if you push the carbs in too far when you mount the carbs to the rubber piece they will not seal properly..
If you mean this , I tried this, not that hard for me to try.

But really impossible.( at least with my bike ) maybe you have other rubbers, i have original.
726347


726348
 

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Discussion Starter #63
Hi guys, the problem(s) is fixed! Finally...
I took the bike to my teacher of mechanics evening course I did last year. He noticed that I didn't have any free play at the throttle handle. (triumphjan did mention this in his last post, but I hadn't checked yet)
This is because when placing the carbs back after disassembly, I didn't put in the throttle cable at the same position at the carbs.
(like I mentioned in post #38)


I didn't realise this small difference could have such a big impact! I almost feel stupid of dis/assembling the carbs a dozen times now...
But off course now I will never forget! And I learned a lot of other stuff.

We also changed the mixture screws setting from 2 1/4 to 2 times out.
Now it runs fine!

The synchronisation settings were still ok.

Some remarks:
  • The throttle cable is at it's minimum setting at carb side and at throttle handle side. The free play is at a bare minimum my teacher said. Is this typical for TBS?
  • Right before maximum throttle, there is a nearly noticeable friction. I guess I will order a new cable.
 
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