DIY carb sync tool revision

  • Injected
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DIY carb sync tool revision

17 Dec 2025 08:52 - 17 Dec 2025 08:55
#919907
I made this manifold for vacuum syncing carbs as my old mercury unit is a bit finicky (low mercury level?) 

 

When I was drilling the holes in the acetal plastic I screwed one up and it got oversized (smallest hole) so one gauge bounces erratically even if the flow knob is dialed right down (SMC flow controls)

I bought some 6061 so I could replace that manifold log and have redesigned the outputs to be at 90 degrees to the gauges so there will be no way the tiny link hole (.032") will get messed up this time.

Looking to get on this before Spring comes.
1978 KZ650B2 w 1197cc Z1 engine
1977 KZ650B1 w 750cc Spectre engine
1979 KZ650C3 w 831cc Hot Rod engine
1978 KZ650C2 w 762cc DFI project
1977 KZ650C1 stock restoration project
1978 KZ650B2 modified project
Last edit: 17 Dec 2025 08:55 by Injected. Reason: sp
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  • Warren3200gt
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Re: DIY carb sync tool revision

18 Dec 2025 03:26 - 18 Dec 2025 03:30
#919914
After accidentally running over my mercury set back in the early 2000's I tried all the usual suspects and concluded they're all pretty rubbish in comparison to the old school mercury set.
This prompted me to make up a fool proof tool that relies solely on simple physics. 
The center ball bearing is the datum point and the outer is open to vacuum from the carb. There is a small restrictor in each side to prevent the ball from getting sucked where it shouldn't go. 
Use carb three as the sync dataum then adjust so the inner and outer balls are directly aligned and those two carbs are perfectly balanced. 

 

 
 

Last edit: 18 Dec 2025 03:30 by Warren3200gt.
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  • kevski
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Re: DIY carb sync tool revision

18 Dec 2025 04:30
#919915
Warren3200gt wrote:
After accidentally running over my mercury set back in the early 2000's I tried all the usual suspects and concluded they're all pretty rubbish in comparison to the old school mercury set.
This prompted me to make up a fool proof tool that relies solely on simple physics. 
The center ball bearing is the datum point and the outer is open to vacuum from the carb. There is a small restrictor in each side to prevent the ball from getting sucked where it shouldn't go. 
Use carb three as the sync dataum then adjust so the inner and outer balls are directly aligned and those two carbs are perfectly balanced. 

 

 
Mine is hanging up in the garage alongside the redundant morgan carb tune.
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  • kevski
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Re: DIY carb sync tool revision

18 Dec 2025 04:33
#919916
My ball bearing one is hanging up in the garage next to my redundant Morgan carbtune. 
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  • Cra-z1
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Re: DIY carb sync tool revision

18 Dec 2025 07:09 - 18 Dec 2025 07:13
#919919
I have used them all but my homemade mercury ones have been the best. Just have to be extremely careful with the mercury. I store the bottle in a secure place when not in use. I was an HVAC tech and the mercury is from many old Honeywell thermostats I had replaced over the years. The ball bearing idea is interesting. 
[img
Last edit: 18 Dec 2025 07:13 by Cra-z1.

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  • Bloobaba
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Re: DIY carb sync tool revision

18 Dec 2025 12:04
#919923
Simple and effective. I made a digital device, and it works well. It can be powered independently with a 12/24V converter or by mains electricity with an adapter. I can also measure the rotation angle of the crankshaft or camshafts with an accessory, an incremental encoder. If needed, I can write a program that can be used for another application.

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Z400F 84 (ZR400B1)
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  • Sheath
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Re: DIY carb sync tool revision

14 Aug 2026 12:44 - 14 Aug 2026 12:45
#926745
I love the ball bearing gauge, that looks very fool proof, whenever I balance my zeds carbs next I'd like to try a bench adjustment first and then the vacuum gauges, the bench adjustment involves using the end of something like a 5mm drill bit and putting it under each slide then adjusting each one so the bit gently drags on the way out like a feeler gauge, of course that wont account for air leaks or compression differences between cylinders so the carbs will still have to be dynamically balanced but it should provide a good base line.... I do like adjusting carbs every so often, it gives me a chance to use the Kawasaki gauge set 
[img
Last edit: 14 Aug 2026 12:45 by Sheath. Reason: Spelling errors

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  • F64
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Re: DIY carb sync tool revision

15 Aug 2026 15:11 - 15 Aug 2026 15:14
#926782
These are all very interesting.
I'm cheap.
When i started messing with the motorcycle i taped some clear tubing to a yard stick. The bend of the tubing was at the lowest point. I held the yard stick vertically and put a little water at the bottom attaching each end to a carb. I had only two cylinders. I watched the cylinders play tug of war with the water. i set the carbs so the tug was equal.

Which is funny when the balance is way off.. The water will get sucked into the stronger carb.
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Last edit: 15 Aug 2026 15:14 by F64.

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Re: DIY carb sync tool revision

15 Aug 2026 22:22
#926795
F64 wrote:
These are all very interesting.
I'm cheap.
When i started messing with the motorcycle i taped some clear tubing to a yard stick. The bend of the tubing was at the lowest point. I held the yard stick vertically and put a little water at the bottom attaching each end to a carb. I had only two cylinders. I watched the cylinders play tug of war with the water. i set the carbs so the tug was equal.

Which is funny when the balance is way off.. The water will get sucked into the stronger carb.

You should try using a restricter in the tubing ends
 

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