Synchronising Vacuum gauges to balance carbs on a GL1000


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GL1000-1976-SCX-593P
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Synchronising Vacuum gauges to balance carbs on a GL1000

Postby GL1000-1976-SCX-593P » Sun Jul 06, 2014 6:23 am



I have refitted my refurbished carbs on my 1976 GL1000, I purchased a set of vacuum gauges to set up the carbs, and started adjusting all gauges on intake 3 setting them all to 21, I then connected all gauges as per the Haynes manual and matched 1 to 3 then 2 to 4 and then as pairs across 2/4 to 1/3 however I could not get the gauges to set any higher than about 16 even though the manual states 21 plus or minus 2.5
Any assistance would be gratefully received.



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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby SteveB123 » Sun Jul 06, 2014 6:56 am

First I've seen an absolute figure for syncing. As long as they are the same number, then the sync is done.
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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby HawkeyeGL1200 » Mon Jul 07, 2014 8:54 am

SteveB123 wrote:First I've seen an absolute figure for syncing. As long as they are the same number, then the sync is done.

+1 to what SteveB123 wrote. It's kind of like a psych exam... no right or wrong answer, as long as you're consistent.

As long as you're keeping all intakes close to the same, matching left & right sides once you get one side even, there is no absolute value for how much vacuum you should see on all the gauges. If you synch with your gauges, then check the synch with a different set of gauges, you will probably see a difference between the sets of gauges... no one I know has their gauge set sent out to get them calibrated...

When using manometers to balance carbs, the manometers must first be "calibrated" by using the "Fixed" carb on your model bike (#3 on GL1100's and #4 on GL1200's... not sure on 1000's, #3 I presume) to ensure all the manometer tubes are calibrated to one carb. My set came with a manifold for doing this. All four tubes are lined up with the fixed carb, and adjusted to read the same level... the "number" on the manometer doesn't matter... then each tube is lined up with the corresponding cylinder... #1 & #3 are synched, #2 & #4 are synched and then 1/3 & 2/4 are balanced to each other, just as you described your balancing... revisit idle RPMs to ensure it doesn't slip away from you, adjusting idle back to 900-1000 as you go.

I'd also run RPMs up to 3000 after you get 1/3 balanced to 2/4 to see what the vacuum looks like at running speeds... after all, most of us don't ride at 1000 RPMs.
I am wrong as often as I am right concerning what is wrong with someone else' motorcycle without having seen the machine in person. Guessing with limited information, as to the source of the trouble, is sketchy at best.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby virgilmobile » Mon Jul 07, 2014 9:11 am

Its true about running at 1000 rpm however that's where you would notice the imbalance.
Sync the carbs keeping the rpm near the 1000 rpm range.just get them all the same.
1000-1200 rpm is where you first take off at and a poor sync will rattle the engine.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby Placerville » Tue Jul 08, 2014 3:07 pm

What type of sync tool did you buy? The gauge or the tube & liquid type.
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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby virgilmobile » Tue Jul 08, 2014 4:06 pm

Well truth be known...Im cheap....I tried the mechanical gages...too difficult to read...tried the oil in the tall tube....sucked the oil right into the cylinder...while great for fogging for mosquitoes...kind of a pain to work with...
I opted for a reserve bottle with old engine oil in it...the vacuum lines are at the top and never suck oil into the cylinder....Matching the sync was easy...just get the levels equal and bubbling the same...
If there is any imbalance,oil is simply migrated to the cylinder that draws more vacuum....

You can see this design and use here...viewtopic.php?f=16&t=8994

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby Placerville » Tue Jul 08, 2014 6:30 pm

Thanks VM, but I was asking ' GL1000-1976-SCX-593P' what type of gauge he was using. ;) ;) (But, I really like your answer. :D )
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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby Fred Camper » Tue Jul 08, 2014 8:58 pm

I use a motion pro and they do not even list a vacuum level anymore and that is just fine. I like the manometer style better than needles as there are less sensitive parts.

I like the idea of doing in a bit higher than 1000 rpm, may try that next time.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby GL1000-1976-SCX-593P » Wed Jul 09, 2014 1:33 am

I was using a 4 bank Vacuum gauge, I managed to balance all 4 at around 16 it was just that the Hayes manual says 21 and I couldnt get it to that so settled for a balanced reading across the 4 gauges.
Thanks everyone for your comments

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby spookytooth » Thu Jul 10, 2014 3:34 pm

Two cheap vacuum gauges will never give the same reading. Better to use one gauge and four valves connected to a manifold.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby mauricejr » Sun Jul 13, 2014 9:00 pm

elevation can make a difference in vacuum reading

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby WingAdmin » Mon Jul 14, 2014 2:20 pm

mauricejr wrote:elevation can make a difference in vacuum reading


In absolute reading, yes. But when balancing carbs, we don't care about the absolute reading; we care only about the differential readings between different carbs. Altitude does not affect this at all, or more accurately, it affects all the carbs exactly the same way.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby spookytooth » Tue Jul 15, 2014 7:58 pm

Could someone point me in the direction to buy the connectors to hook the vacuum hoses to the intakes?

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby WingAdmin » Tue Jul 15, 2014 8:55 pm

spookytooth wrote:Could someone point me in the direction to buy the connectors to hook the vacuum hoses to the intakes?


Motion Pro sells them: http://www.motionpro.com/motorcycle/partno/08-0218/

I would not recommend that you leave them in place like they say - all it takes is one of those little rubber caps falling off to strand you somewhere.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby spookytooth » Tue Jul 15, 2014 9:48 pm

After a bit of research I found these that should work just fine...

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... ink:top:en

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby Fred Camper » Fri Jul 18, 2014 6:23 pm

Seems like those would work just fine, look like the pro-motion ones. Just need to be sure there is room for the hex, I suspect there is.

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby GL1000-1976-SCX-593P » Sat Jul 19, 2014 2:26 am

I have looked at the 4 brass connectors, the only doubt I would have is that they have a significantly larger hole than the standard tubes that come with the gauges.....

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Re: Synchronising Vacuum gauges to balance carbs on a GL1000

Postby Fred Camper » Sat Jul 19, 2014 9:44 am

It is essential that the hoses are damped, otherwise even the fluid columns dance. My set came with restriction in the hose that just have a pin hole. You can also use aquarium clamps to restrict. Those may not really make any difference once you put a proper restriction into the line.




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