Carburetor sync gauges

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Carburetor sync gauges

#1

Post by mikenixon »

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Professional mechanics see carburetor synchronization differently from the rest of the world. While the general public views it like the wash you give your ten-year-old car once a year out of guilt-- far from that, carburetor adjustment and synchronization is actually the capstone of the engine part of the preventative maintenance tetralogy that includes compression, valves, and ignition; and that in turn part of the complete routine that Honda calls for every 3,000 miles. 1 Synchronization is so important, and so effective, and at the same time so rarely practiced I am convinced that for many of my customers a good carb sync is just as beneficial as anything else done to their carburetors during the rebuild. For some I am sure it is the only time it ever happens or happens accurately.

The outcome of precise carburetor adjustment and synchronization is for me, even after nearly five decades, invariably astonishing, marvelous. Mechanics don't take carburetor synchronization lightly. It may be a once-in-a-lifetime event for many, but it is far from that to us. Thus we value it, believe in it. And the tools we use reflect that. One outcome of the following study is that it eliminates the excuse many make that the right tools are too expensive. The difference between the tool most are buying and one or two that are many times better is surprisingly little. 2

Here then is a comparative analysis of carburetor synchronization measuring tools, often called manometers in the trade. I looked at more than 30 different models, and reduced this review to sixteen representative tools. My goal is not necessarily to come up with the best, or generate debate over water versus mercury versus Bourdon tube versus metal rod versus digital. Nor is this an exhaustive report. The focus is quality, and except where I have firsthand knowledge, performance is implied by the fitness of the tool for the job. I have tried to do just two things. The first is to point out why some of these tools are better than others. The second is to reinforce my favorite theme, that is, best practice. I am encouraging you to make carburetor synchronization a habit.

https://motorcycleproject.com/text/SYNC ... ARO_v2.pdf

Speaking of quality, one thing has to be said; one important tenent must be established. Though an old design and not as flashy as other types, a set of mechanical vacuum gauges can be extremely accurate. 3 With one caveat. That caveat is, to be accurate, a set of mechanical gauges absolutely must employ calibration screws that permit the individual mechanically driven gauges to periodically be matched to each other to compensate for wear and minute differences in manufacture. Mechanical gauges that lack this feature are simply not to be trusted, not just in theory but in stark reality. Villify me if you must, it's just a fact and one I have proven many many times.

Because tables offer the only sensibly compact way to do this article, and the forum does not accomodate tables, I have posted this sync gauge comparison on my website for viewing. You'll be pleased to know I made it a pdf so you can download it and store or print it, if that interests you. Feedback in this thread is welcomed.

I leave you with a bit of a tease. This tool is included in my article, with comments. Does anyone know what it is? A rare item, I have seen only one of these in my more than 46 years in the trade.

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1 Vintage owners who take a year to accumulate that should do a complete maintenance service every six months instead.

2 In fact, the most popular synch tool on forums cost more than twice as much as one in the comparo that is measurably better.

3 Mechanical gauges are technically known as Bourdon tube type because they employ internally a pressurized curled brass tube that uncurls to move the needle.

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Re: Carburetor sync gauges

#2

Post by Whiskerfish »

"Like" Many folks definitely undervalue the bennefits of a quality synch.
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and a whole garage full of possibilities!!

Psst. oh and by the way CHANGE YOUR BELTS!!!!
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Re: Carburetor sync gauges

#3

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I still have the old Motion Pro mercury sticks (because a buddy gave them to me, and I'm cheap). At least calibration is not an issue, and I am cautious with the mercury. I still have the bottle that the mercury supply came in, and have never had to add any to the reservoir through 5 'Wings and a CB750F DOHC. I find them easy to use if a bit awkward to get the tubes to reach at times. I first tried hanging them off of a mirror, but now use a photo tripod so the height can be adjusted for both best viewing and reaching the taps. I might extend the lines soon just to make it a lot easier to hook up. Might also make some easier to attach and better sealing adapters with o-ring groves that not just squish the o-ring but force a seal to the tube. The simple nut arrangement is a bit sloppy. I need to rebalance all three of my 1000s soon due to time and some other adjustments. It will be interesting to see how changing the '75s ignition to Dyna and the '79s to TFI triggered by points has affected balance. Shouldn't, but....
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Re: Carburetor sync gauges

#4

Post by mikenixon »

:)
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Re: Carburetor sync gauges

#5

Post by Track T 2411 »

I bought the Carbtune a few years ago after trying to build a 'home brew' unit. I shied away from the gauge- type offerings mostly because they seem cheaply made, and I couldn't understand the wide range in price. Your comparisons certainly help me understand that part of the equation.
As for accuracy (the Carbtune), I'm assuming you mean consistency between each if the four columns, correct? How would one go about checking them? Swapping the tubes between cylinders, or using a vacuum pump such as a MityVac?
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Re: Carburetor sync gauges

#6

Post by nakedinterstate81 »

Mike, Can you recommend a particular one that does an adequate job and doesn't break the bank?
I am currently looking to buy one.
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Re: Carburetor sync gauges

#7

Post by pidjones »

Track T 2411 wrote:I bought the Carbtune a few years ago after trying to build a 'home brew' unit. I shied away from the gauge- type offerings mostly because they seem cheaply made, and I couldn't understand the wide range in price. Your comparisons certainly help me understand that part of the equation.
As for accuracy (the Carbtune), I'm assuming you mean consistency between each if the four columns, correct? How would one go about checking them? Swapping the tubes between cylinders, or using a vacuum pump such as a MityVac?
Simply inter-connect the four.
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Re: Carburetor sync gauges

#8

Post by Track T 2411 »

pidjones wrote: Simply inter-connect the four.
Ah... use a tee with one vacuum source. Duh...
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Re: Carburetor sync gauges

#9

Post by mikenixon »

Track T 2411 wrote:I bought the Carbtune a few years ago after trying to build a 'home brew' unit. I shied away from the gauge- type offerings mostly because they seem cheaply made, and I couldn't understand the wide range in price. Your comparisons certainly help me understand that part of the equation.
As for accuracy (the Carbtune), I'm assuming you mean consistency between each if the four columns, correct? How would one go about checking them? Swapping the tubes between cylinders, or using a vacuum pump such as a MityVac?
Hi, Track...

I anticipated someone would ask. When I managed dealer training for Kawasaki I bought 12 of the Carbtune Pros (made in England) to supply the company's 6 training centers. Thought they would be good. Thus I also recommended them to anyone who would ask. Then one of the folks I recommended them to brought his to me to test with my 5-1 manifold special tool. Disallusionment. I found them reading all over the place, and one column was over two inches out. This could have been just a single bad unit and I suggested he get the company to replace it. But it kinda soured me on the Carbtune.
Last edited by mikenixon on Wed Jun 17, 2020 4:10 pm, edited 1 time in total.
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Re: Carburetor sync gauges

#10

Post by mikenixon »

nakedinterstate81 wrote:Mike, Can you recommend a particular one that does an adequate job and doesn't break the bank?
I am currently looking to buy one.
Though I loathe Chinese tools as much as the next guy, the EBay/Pep Boys ones with the calibrating screws would seem to be the best buy at just $40. I see a member here has already confirmed that the screws on the faces are indeed calibrating screws.

https://www.ngwclub.com/forum/viewtopic.php?f=8&t=31575

Personally, if it were me and my uber nice set (the 1969 Honda set) was stolen, I might go for the Boehm. There seem also to be a couple dozen reasonably priced digitals available now and those, though so new there is no history, these should be considered also. Money no object? The $700 Kowa from Webike. Even that high price would be worth it if you can stand the freight and it would still be less than trying to replace my 60s Honda set.
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Re: Carburetor sync gauges

#11

Post by mikenixon »

pidjones wrote:I still have the old Motion Pro mercury sticks (because a buddy gave them to me, and I'm cheap). At least calibration is not an issue, and I am cautious with the mercury. I still have the bottle that the mercury supply came in, and have never had to add any to the reservoir through 5 'Wings and a CB750F DOHC. I find them easy to use if a bit awkward to get the tubes to reach at times. I first tried hanging them off of a mirror, but now use a photo tripod so the height can be adjusted for both best viewing and reaching the taps. I might extend the lines soon just to make it a lot easier to hook up. Might also make some easier to attach and better sealing adapters with o-ring groves that not just squish the o-ring but force a seal to the tube. The simple nut arrangement is a bit sloppy. I need to rebalance all three of my 1000s soon due to time and some other adjustments. It will be interesting to see how changing the '75s ignition to Dyna and the '79s to TFI triggered by points has affected balance. Shouldn't, but....
I've never liked the vacuum probes made of brass modelling tubes with nuts threaded on. Find a shop that has an K&L account and you can buy from them very nice nachined, silver-soldered, knurled probes with o-rings set in machined grooves very similar to what Honda used to have.

By the way, the mercury gauges are still available.
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Re: Carburetor sync gauges

#12

Post by ericheath »

Over 100 foot tall buildings are kept plumb using plastic tubing and colored water. I still think a modest medium of oil, ATF, whatever is all you need. I have two Tees side-by-side. Four equal lengths to reach the four ports are connected to the two sides of the Tees that are opposite from each other. The two lower parts of the Tees are connected to a longer length of tubing, 5-8’?? These hold the oil and in the top of mine, right before the TEE I put an old float valve. A jet would work too to slow the bounces down. Not very sophisticated looking, but sure seems to get the job done.

I plug one side from each TEE and use the other sides on the ports to match 1-3, then close the 1-3 ports and match 2-4, then hook up all four and match 1-3 side to 2-4 side. Theoretically you shouldn’t need all four.

No calibrating, just keep them being bent, kinked or mangled. If they’re quite far out of sync, you will need to shut it off quickly so you don’t have one side pull all your lights out. A few guess-and-checks and you’re there.

One or more cylinders with bad compression could create problems. I’m not sure gauges could remedy that either.

This summer I haven’t synced any. Hard to do when the pieces are all up in the rafters.

I once tried the method where you hold each tube up into your ear. That was a laugh.
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Re: Carburetor sync gauges

#13

Post by mikenixon »

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This is what I use to recalibrate my Marsh gauges every so often.
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Re: Carburetor sync gauges

#14

Post by mikenixon »

ericheath wrote:Over 100 foot tall buildings are kept plumb using plastic tubing and colored water. I still think a modest medium of oil, ATF, whatever is all you need. I have two Tees side-by-side. Four equal lengths to reach the four ports are connected to the two sides of the Tees that are opposite from each other. The two lower parts of the Tees are connected to a longer length of tubing, 5-8’?? These hold the oil and in the top of mine, right before the TEE I put an old float valve. A jet would work too to slow the bounces down. Not very sophisticated looking, but sure seems to get the job done.

I plug one side from each TEE and use the other sides on the ports to match 1-3, then close the 1-3 ports and match 2-4, then hook up all four and match 1-3 side to 2-4 side. Theoretically you shouldn’t need all four.

No calibrating, just keep them being bent, kinked or mangled. If they’re quite far out of sync, you will need to shut it off quickly so you don’t have one side pull all your lights out. A few guess-and-checks and you’re there.

One or more cylinders with bad compression could create problems. I’m not sure gauges could remedy that either.

This summer I haven’t synced any. Hard to do when the pieces are all up in the rafters.

I once tried the method where you hold each tube up into your ear. That was a laugh.
That piece of radiator hose held to the ear deal seems to be a trick vintage Italian sports car mechanics use. The oil thing you're doing reminds me of snowmobile manuals that recommended engine coolant inside a pair of very long hoses.
Last edited by mikenixon on Wed Jun 17, 2020 4:46 pm, edited 1 time in total.
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Re: Carburetor sync gauges

#15

Post by mikenixon »

And no one is going to comment on this tool?

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