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Discussion Starter #1
Service manual states to return the mixture screws to the same number of turns before you rebuilt the carbs. What if one of them was 5 1/2 turns and the other was 3? Could they be that different?
 

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If someone was messing with them, then yes,
Start with factory recommended setting, but the best way is to do a vacuum carb sync to really dial them in.
 

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Discussion Starter #5
Started with 2, then tried 2 1/2. No change. I have some other problems (see my "In case you missed it...' post in the 500 section).
 

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If someone was messing with them, then yes,
Start with factory recommended setting, but the best way is to do a vacuum carb sync to really dial them in.
Ouch! I thought the sync screw was the only adjustment for carb synching. I have been adjusting the low speed jets for highest and best idle and then synching with just the sync screw and leaving well enough alone. Are you suggesting going back and forth between the sync screw and the mixture screws? If you don't mind my asking, is there a better procedure?
 

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I'd recommend returning to baseline settings, both throttle plate (synch) and mixture.

The LH carb is the "master", the synch screw actually adjusts the throttle plate of the RH carb only.

You may have noticed the carb synch screw factory painted yellow....their way of "sealing" the screw from rotation. The factory perfectly matches the plates, the pilot screws are commonly widely mismatched. I think Keihin uses a billion dollar flow machine before the carbs ever reach the bike.

Pulling the carbs, and visually matching the throttle plate openings reestablishes the baseline on synch.

A baseline for the pilot screws is 2.5 turns from lightly seated.

With these baselines met, the bike should readily start, idle and accept throttle, provided the circuits are, in fact clear and the fuel levels have been set.
This also assuming the other tuning parameters on the bike are ok (spark plugs, air filter, battery, etc etc.

If the pilot screws are not affecting RPM at all...the offending pilot circuit is clogged or other issues are present. The tiny pilot orings are important little buggers to renew, as well.

Did you actually disassemble and rebuild your carbs? Were the fuel levels set?
 

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Discussion Starter #9
... The tiny pilot orings are important little buggers to renew, as well.

Did you actually disassemble and rebuild your carbs? Were the fuel levels set?
Thanks, Ducati. Yes, the full rebuild kits were used. I had free flowing pressurized carb cleaner (from a can with straw) flowing through all passages, or so I thought. Yes, the fuel levels in the bowls were correct- I didn't need to adjust the floats.

I guess it's time to take the carbs off again. I just wonder how I will avoid damaging the O-rings that seal around the mixture needles, as it was tough digging out the old ones.
 

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Discussion Starter #10
The correct way to synch cabs is by vacuum readings. Eyeballs are not good enough.
I think I was in spec there - only about a 1/2" of vacuum difference between the two. Did my reading on 9 inches mean anything, or would we have to have known the RPMs to decipher anything?
 

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At factory specified idle speed, both carbs should pull same maximum vacuum.

Did you use a modified gauge to eliminate needle bounce or sticks?
 

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Discussion Starter #13
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Did you use a modified gauge to eliminate needle bounce or sticks?
I don't know. It's an old automotive vacuum gauge. It bounced all over during cranking, but was steady while running. As far as sticking; again, it seemed to move accurately when the hose was clamped.
 

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Discussion Starter #14
As an add, valves must be correctly adjusted before any sync. work is done or you are wasting your time.
I was just trying to make sure things weren't totally out of whack. When I took the carbs off the first time, one mixture screw was 2 1/2 turns off seated and the other was over 5. I had ridden this bike before it went into 'stasis', and the throttle response was very slow and it wouldn't rev very high at all.

I've posted the results of today's test over in my thread in the 500 section, under "In case you missed it in the new member area...". For the sake of avoiding confusion or duplication, I won't post in this thread again.

Thanks.
 
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