My Homemade Manometer

[castlekin]

So, I took a 3/16 x 12 brake line I had laying around, or also known as 4.7mm X 30.5mm. I cut off about 3 inches of it, threaded it though a M5 thread die, and put on a 007 o-ring on that. I need to get a few nuts on those, but they thread into the carb boots very well and I am able to make them the length I need.

Hope that helps others to make those adapters a little cheaper.

[kcorbin]

So, I took a 3/16 x 12 brake line I had laying around, or also known as 4.7mm X 30.5mm. I cut off about 3 inches of it, threaded it though a M5 thread die, and put on a 007 o-ring on that. I need to get a few nuts on those, but they thread into the carb boots very well and I am able to make them the length I need.

Hope that helps others to make those adapters a little cheaper.

I tried that same thing with the brass tubing as well as some stainless steel I had and couldn't get it to thread. But, that was more of a factor of my poorly designed Harbor Freight tap & die set. The taps seemed to be just fine but the dies didn't have enough 'slope' or 'graduation' at the mouth to actually accommodate the stock and start cutting new threads. It works fine for chasing threads to clean them up but not actually creating new ones.

I tried it first because I thought drilling all the way through center of the 5mm socket head screws would not be easy but it ended up being no big deal. No drill press and it still worked out great.

[850GT_Rider]

What is the actual measurement

I may have access to some guages and build my own manometer. Anyone know what the actual suction measurement is? Either in inches of water or inches of mercury?

[MAdams450]

I am not positive if this is correct, but I was once told by a suzuki mechanic that the reason for the unbalance when syncing has to do with cylinder cooling.(inner 2 cylinders dont run as cool as outer 2).

[Steve]

I am not positive if this is correct, but I was once told by a suzuki mechanic that the reason for the unbalance when syncing has to do with cylinder cooling.(inner 2 cylinders dont run as cool as outer 2).

Then why was it specified for the bikes that had crossovers in the exhaust?

Or was it just coincidence that the specified imbalance just happened to come at the same time as the crossovers?

.

[850GT_Rider]

I may have access to some guages and build my own manometer. Anyone know what the actual suction measurement is? Either in inches of water or inches of mercury?

Anyone? Bueller??

[BassCliff]

Hi,

I may have access to some guages and build my own manometer. Anyone know what the actual suction measurement is? Either in inches of water or inches of mercury?

The actual vacuum measurements will vary with the rpm speed. The factory manual states no hard and fast numbers and the factory tool has no numbers on it at all, only balls in cylinders to represent the vacuum balance between the cylinders.

I have a few pictures of my Morgan Carbtune from which you can get a general idea of how much vacuum we're talking about. These pictures were taken at 2000-3000 rpm.

This is at idle, before synchronization:



You see the vacuum varies between 14 cm/Hg and 18 cm/Hg.

This is at ~2000 rpm:



You see the variance is between ~21 cm/Hg and 26 cm/Hg.

This is after synchronization, again about 2000 rpm:



You'll notice the vacuum between 22 and 24 cm/Hg.

Here are a couple of illustrations from the factory manual. Notice, no numbers.

For the bikes with exhaust crossovers:



For bikes without exhaust crossovers:



I would think that gauges that read 0 - 50 cm/Hg would suffice. It seems that the Morgan Carbtune reads from 8 - 42 cm/Hg. I'll let you do the math to convert to inches.

Thank you for your indulgence,

BassCliff

[850GT_Rider]

That's perfect Cliff - Thanks!

Edit: I know we're more interested in the difference (delta p) than in the actual number, and now I know that 0-60" H20 gauge will be perfect. I can get those fairly easily - we use them all the time. I'll put snubbers in the tubing to quiet down the oscillations and be good to go!

[kcorbin]

Then why was it specified for the bikes that had crossovers in the exhaust?

Or was it just coincidence that the specified imbalance just happened to come at the same time as the crossovers?

.

I don't think it has to do with the crossovers. The 550 has crossovers for both the 79 and 80 model years yet the 79 factory manual says to sync straight level across all the balls. In the 80 manual it says to sync 1 and 4 even, and 2 and 3 even, but slightly lower than 1 and 4. The major change in 80 was moving from the VM22 carbs to the BS32 (constant velocity) carbs. It would seem that the carb type is probably the overriding factor and not the exhaust type.

Interestingly, the Haynes manual states the VM22 carb is actually slightly undersized for that engine at higher RPMs and recommends swapping for the larger BS32 for performance. So then, does cooling the inner two cylinders more come into play when you are pushing the engine harder with the larger carbs? Or, is it just a function of how the new CV carbs work? I can't tell *for sure* in BassCliff's pictures, but I bet the first picture showing the un-aligned balls is with a BS/CV carb.

[hampshirehog]

I tend to agree that the 'unbalanced' carbs are required because of the airbox rather than the exhaust. If you balance the carbs with the airbox fitted as per the handbook and then without the box on the gauges become level ( or more level - is 'leveller' a word...?). And this is for the CV carbs - the VMs are in comparison crude old things that are pretty insensitive.

Is the Suzuki manual wrong (again)?

In practice I have never found one iota of difference between carbs balanced evenly across all 4 or with the half a ball difference so I just set them all level now.

[BassCliff]

Hi,

I can't tell *for sure* in BassCliff's pictures, but I bet the first picture showing the un-aligned balls is with a BS/CV carb.

Yes, that first picture is with CV carbs. You may be on to something. The difference in balancing could very well be a carb issue or a combination of carb/crossover exhaust.

I try not to think too hard about these things. I just fix it according to the book and it works. But I have also experimented and set up my balance both ways and haven't really noticed a difference.


Thank you for your indulgence,

BassCliff



Thank you for your indulgence,

BassCliff

[Steve]

I don't think it has to do with the crossovers. The 550 has crossovers for both the 79 and 80 model years yet the 79 factory manual says to sync straight level across all the balls. In the 80 manual it says to sync 1 and 4 even, and 2 and 3 even, but slightly lower than 1 and 4. The major change in 80 was moving from the VM22 carbs to the BS32 (constant velocity) carbs. It would seem that the carb type is probably the overriding factor and not the exhaust type.

I'll agree with part of that, but not all.

I just checked a couple of vendor's sites, the '79 550 did NOT have a crossover in the exhaust.

I don't think that any of the 4-cylinder bikes with VM carbs had a crossover tube when they left the factory.
30+ years of "previous owners" have left bikes with all manner of systems that carry the fumes.

I tend to agree that the 'unbalanced' carbs are required because of the airbox rather than the exhaust. If you balance the carbs with the airbox fitted as per the handbook and then without the box on the gauges become level ( or more level - is 'leveller' a word...?). And this is for the CV carbs - the VMs are in comparison crude old things that are pretty insensitive.

I have never compared 'balanced' carbs with and without an airbox, but that is rather intriguing. Have you tried the same thing with VM carbs?
I just can't picture why the airbox would make a difference between the carbs and engine, but anything is possible.

In practice I have never found one iota of difference between carbs balanced evenly across all 4 or with the half a ball difference so I just set them all level now.

I agree with that. In my ignorance in the "early years", I simply set them all at the same level. When I learned that Suzuki recommended a different setting, I tried it, but could not tell the difference. Since we really have no idea just how much of a difference "half a ball" is, I will continue to set them rather equally, but if the inner cylinders are just a bit lower, I let it ride and don't bother trying to change them.

.

[kcorbin]

I'll agree with part of that, but not all.

I just checked a couple of vendor's sites, the '79 550 did NOT have a crossover in the exhaust.

I don't think that any of the 4-cylinder bikes with VM carbs had a crossover tube when they left the factory.
30+ years of "previous owners" have left bikes with all manner of systems that carry the fumes.

.

Actually, if you look at the 'L' model for '79 it does have a crossover tube (yes, 'E' does not) but there is no change in the manual for syncing the 'L' compared to the 'E'. But then, the 'L' also got an integrated regulator/rectifier so it must have had all the 'fancy' upgrades!

[kcorbin]

It took me a while, but I finally got around to splicing and posting a video of the manometer in operation with a detailed explanation.

You can check it out here: http://www.youtube.com/watch?v=GaTRy...ature=youtu.be

Cheers!

[Steve]

WOW.

HOLY COW!

What else can I say?

How FAST was the engine running while you were doing the second half of that video?

Sounds like it was doing about 2500-3000 rpm (or more).

Try it again, but somewhat closer to the factory-recommended speed of 1500-2000 or where most of us actually do it, about 1100, right at idle speed.

The sync has the greatest effect right at idle speed, that is where it should be checked.

Hope it works out for you, but that is far too long running the engine for a carb sync in my book.

Also, never saw how much time and or effort was necessary to get liquid back into that empty bottle.

Still not sure that is accurate, but lilke you said at the end "will have to check this against a Carbtune or other gauge".

Thanks, I'll stick to my mercury sticks and get a Carbtune if they ever fail.

.