Carb balancing

Got a tough one for you to crack. For many years I have been setting up my carburettors using a homemade u-tube barometer. Basically, some clear plastic tubing with some oil in it fixed to the garage wall. It always worked a treat. Lately, however, I’ve hit a problem. If I balance the carbs this way, so that the oil levels in both sides of the u-tube are the same, the bike runs rougher than a badger’s you-know-what. Setting it up “by ear” or using the plug shorting method, results in the old girl running as smoothly as Swiss clockwork, while the oil levels in the u-tube are inches apart. Recently had the carbs apart to do a rebuild with the repair kit from Motorworks. Made no difference. Also replaced the rubber carb to head tubing thingies in case they were leaking. No difference. The right hand cylinder/piston is a relatively recent replacement, with new rings. But they should be run in by now. And its not as if I cannot get her to run smoothly. Over to you lot!

It does seem vacuum related from what you have said above. The 1st thing to try would be to substitute the test equipment for a known carb balancer just to tick that off. Also check the carb vacuum take off point is not blocked before further testing.

Are your vacuum take off ports clear?

Yes the vacuum ports are both clear.

PHILIPHUW said:

And its not as if I cannot get her to run smoothly. Over to you lot!

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Discard Manometer Set up by ear and ride it!

Carb rebuild Hmmmm Got one plug sootier than the other by any chance ??

How come piston and barrel replaced only on one side ?
Be interesting to do a compression/leakdown test on both sides for comparison ?

SteveHop said:

How come piston and barrel replaced only on one side ?
Be interesting to do a compression/leakdown test on both sides for comparison ?

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This