How to synchronize your carburetors


Step-by-step tutorials on how to maintain and fix your GL1100
  • Sponsored Links
robertdawber
Posts: 285
Joined: Fri Aug 07, 2009 9:24 pm
Location: Eliot, ME
Motorcycle: 1983 GL1100 Interstate

Re: How to synchronize your carburetors

Post by robertdawber » Wed May 05, 2010 11:42 am



jackknife wrote:I figured I would throw out another way of syncing the carbs...

I just use the 5mm adapters, a piece of clear vinyl tubing and some water. I put enough water in the tubing to fill about 2 feet of it. Then I lay the tubing over my handlebars so that the middle part with the water is hanging over the front and the ends are near the engine. I connect the ends to two carburetors at a time. By watching the level of water in the tube, it is easy to tell if one carburetor is pulling more vacuum than another.

In my personal opinion, this method tends to be more accurate than comparing mechanical gauges and safer than messing with mercury. It also doesn't hurt that it costs next to nothing. ;-)
Why in the world would you take that risk??
It sounds way too risky to me.
What I am doing is taking from the "How to" method and instead of using four gauges I am using one.
I am using an aquarium "four way gang valve" http://www.petco.com/product/6239/PETCO ... alves-6239
and the other items Scott listed.
Then I do not need to calibrate my gauges and will have all four carbs still hooked up at the same time.
I am still waiting for the 5mm adapters to arrive-(I have plenty still to do before hand) but will take a photo when the come.
Messing with water near a carb. sounds like bad news waiting to happen
Bob



User avatar
tumunga
Posts: 97
Joined: Sun Jun 21, 2009 10:34 am
Location: United States
Motorcycle: 1989 GL1500 - this is the one I will always need help with.

1980 GL1100I Interstate (gone)

Re: How to synchronize your carburetors

Post by tumunga » Wed May 05, 2010 2:19 pm

I don't know much about this kind of stuff, so don't take this the wrong way. How would water get into the carburetors from connecting the tubes at the bottom of the intakes? Does the vacuum created draw into the cylinder, or is it being drawn back into the carburetor? I would think the vacuum would be drawn into the cylinder because that's where the fuel is going, but that's just my dumb mind trying to wrap itself around this subject. A little measured water in the cylinder wouldn't hurt anything, would it?
Tumunga
1989 GL1500 Goldwing with all the optional goodies (I think)

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Wed May 05, 2010 3:02 pm

The vacuum is created by the cylinders pulling air through the intake valves as the pistons move down in their bore. Normally, this sucks the air through the air filter, through the carburetor venturi, where fuel is introduced and mixed with the air, through the intake manifold, and into the cylinder.

When you plug that vacuum gauge (or hose with water) into the intake manifold, it presents that vacuum to your gauge as well, so you can measure it. The vacuum occurs because the throttle plate in the carburetor is restricting the airflow when the cylinder is sucking the air.

Balancing the carburetors is making sure each carburetor is restricting the airflow the same amount.

What happens if water gets sucked into the intake manifold? It depends. If just a little bit of water gets sucked in, it will likely steam clean the cylinder and spark plug and exit the exhaust as steam.

However, if more water gets sucked in - more than 20cc or so (about 0.6 oz) there is a significant chance of damage. After the intake valve closes, the piston moves up in the cylinder bore, compressing the air/fuel mixture. On a GL1100, the compression ratio is 9.2:1 - so each of the 1085cc GL1100's engine cylinders compresses its 271cc of fuel/air mixture down to only 29.5cc. The problem is, water doesn't compress. So if it's sucked 20cc of water into a 271cc cylinder, and is now trying to cram that down to only 29.55cc - that leaves less than 10cc for the fuel/air mixture to occupy. It will detonate before the piston reaches top dead center, at best causing a big bang, at worst bending a connecting rod, breaking a piston, bending the crank and/or blowing out a head gasket.

Let's say 30cc of water gets sucked in - remember, that's only about 1 oz. The piston will attempt to compress this down to 29.5cc - but water does not compress. This WILL cause at best a bent connecting rod, at worst a destroyed engine.

User avatar
tumunga
Posts: 97
Joined: Sun Jun 21, 2009 10:34 am
Location: United States
Motorcycle: 1989 GL1500 - this is the one I will always need help with.

1980 GL1100I Interstate (gone)

Re: How to synchronize your carburetors

Post by tumunga » Wed May 05, 2010 3:36 pm

A-ha! That makes a lot of sense sir...just what I was thinking...but not as technical! :lol:
Tumunga
1989 GL1500 Goldwing with all the optional goodies (I think)

User avatar
djoyner
Posts: 43
Joined: Fri Nov 20, 2009 12:10 pm
Location: Chesterfield County, Virginia
Motorcycle: 1978 GL1000
1985 GL1200 Interstate
1995 GL1500 Interstate
2006 VTX 1300S
Contact:

Re: How to synchronize your carburetors

Post by djoyner » Thu May 06, 2010 9:38 am

Does the 1200 use 5mm or 6mm adapters?

Thanks.
D J
2006 VTX 1300S
1978 GL1000
1985 GL1200 Interstate
1995 GL1500 Interstate

Visit me at:[url http://www.dennisjoyner.net][/url]

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Thu May 06, 2010 10:29 am

djoyner wrote:Does the 1200 use 5mm or 6mm adapters?

Thanks.
The 1200 uses 5mm adapters.

User avatar
djoyner
Posts: 43
Joined: Fri Nov 20, 2009 12:10 pm
Location: Chesterfield County, Virginia
Motorcycle: 1978 GL1000
1985 GL1200 Interstate
1995 GL1500 Interstate
2006 VTX 1300S
Contact:

Re: How to synchronize your carburetors

Post by djoyner » Thu May 06, 2010 11:28 am

Wing Admin,

Thanks for the quick response.
D J
2006 VTX 1300S
1978 GL1000
1985 GL1200 Interstate
1995 GL1500 Interstate

Visit me at:[url http://www.dennisjoyner.net][/url]

stuhrdw
Posts: 6
Joined: Thu Jul 23, 2009 8:46 pm
Location: Parker, co

Re: How to synchronize your carburetors

Post by stuhrdw » Thu May 06, 2010 5:20 pm

I did the compression check on cyl 4 and it was next to nothing, about 8 PSI, the adjacent cyl was normal, but maybe a little low as it is cold.

I am hoping it is just a unseated or burned valve, I am pulling the head now.

stuhrdw
Posts: 6
Joined: Thu Jul 23, 2009 8:46 pm
Location: Parker, co

Re: How to synchronize your carburetors

Post by stuhrdw » Sat May 08, 2010 6:54 pm

Pulled the head and the valves and the Intake for #4 is slightly bent and was unseated. How does this happen? I ordered a new valve and decided I am going to pull the head from the other side and lap each valve there as well because the left side was kinda nasty.

robertdawber
Posts: 285
Joined: Fri Aug 07, 2009 9:24 pm
Location: Eliot, ME
Motorcycle: 1983 GL1100 Interstate

Re: How to synchronize your carburetors

Post by robertdawber » Sat May 08, 2010 9:08 pm

I have a question-in one of the instructions, Scott, you said that all one needs to do is open the valve (aquarium) enough for a flow of a vacuum.
I found that these little valves are tough to regulate. How did you know each was allowing a similar flow?
Also, my bike seems to all sync at about 24 on the gauge (same one you are using) Yours look to be about 20 or so,
Bob

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Sun May 09, 2010 9:41 am

The adjustment of the little valves can be tricky. You want them to be closed enough to dampen the oscillations, but open enough so that they don't restrict it so much that they indicate an incorrect amount of vacuum. I found that closing them to the point that the indicated vacuum starts to decrease, then opening them back up just slightly, was the best way to do it.

Also, thinking about it now, it would probably be best to put the little valves as close to the engine as possible, to leave a larger amount of "buffer" in the air lines to help absorb the oscillations. Technically, you could put a large rigid bottle or other thing that would present a large volume of air, to further dampen the oscillations, but still present the correct amount of vacuum to the gauge.

robertdawber
Posts: 285
Joined: Fri Aug 07, 2009 9:24 pm
Location: Eliot, ME
Motorcycle: 1983 GL1100 Interstate

Re: How to synchronize your carburetors

Post by robertdawber » Sun May 09, 2010 10:10 am

WingAdmin wrote:The adjustment of the little valves can be tricky. You want them to be closed enough to dampen the oscillations, but open enough so that they don't restrict it so much that they indicate an incorrect amount of vacuum. I found that closing them to the point that the indicated vacuum starts to decrease, then opening them back up just slightly, was the best way to do it.

Also, thinking about it now, it would probably be best to put the little valves as close to the engine as possible, to leave a larger amount of "buffer" in the air lines to help absorb the oscillations. Technically, you could put a large rigid bottle or other thing that would present a large volume of air, to further dampen the oscillations, but still present the correct amount of vacuum to the gauge.
Yes, that is pretty much what I figured too-
What about the 20 vs. 25 from my reading to yours?

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Sun May 09, 2010 4:03 pm

It could be a difference between the calibration of the vacuum gauges themselves...I don't put a lot of trust in the calibration of cheap Harbor Freight gauges. As long as one is consistent to match against the others. :)

Trickster
Posts: 7
Joined: Sun May 30, 2010 12:34 pm
Location: Alberta, Canada
Motorcycle: 1978 GL1000
1979 CX500 C

Re: How to synchronize your carburetors

Post by Trickster » Sun May 30, 2010 8:21 pm

Awesome....tyvm for the tutorial on synchronizing.

78 GL1000...would it be 5 or 6 mm adaptors?

Thanks,
Rick

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Mon May 31, 2010 8:16 am

GL1000's use 5mm adaptors.

User avatar
WingAdmin
Site Admin
Posts: 19691
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: How to synchronize your carburetors

Post by WingAdmin » Mon May 31, 2010 8:44 am

Incidentally, the last time I did this a few weeks ago, I was having trouble keeping track of the differences in my vacuum gauges. The gauges are not calibrated exactly, so there are differences between them. I was trying to remember "this one reads 1.5 inches high, this one reads 2 inches low" and so on - impossible! I decided that seeing as you are only ever actually adjusting between two carbs at a time, I would use ONE gauge to balance all of them.

The way I did this was using the "T" that came with the Harbor Freight gauges. I installed the tubes on the two carbs to be balanced, with the valves as close to the carbs as possible. Each of those tubes went to the "T", and I had one hose run from that "T" to the gauge:

Image

Open the first valve and close the second, then read the reading on the gauge. Next, close the first valve and open the second, and read its reading on the gauge. Then make adjustments to make them match. This way, you don't have to calibrate the gauge: just match the readings between the two carbs you're working on. It's simple, it's quick, and when you're working with gauges that may not be perfectly calibrated, it's far more accurate.

mooseye
Posts: 10
Joined: Sun May 23, 2010 10:10 pm
Location: Cleveland,TN
Motorcycle: 1990 GL1500 SE Red

Re: How to synchronize your carburetors

Post by mooseye » Tue Jun 01, 2010 12:08 pm

different rpm? The numbers are relevant only to each gauge, not the prescribed amount of running vacuum.
What about the 20 vs. 25 from my reading to yours?

snowy.vtwin
Posts: 25
Joined: Mon Aug 24, 2009 11:48 am
Location: Marquette, Michigan
Motorcycle: '85 GL1200A
'95 Shadow ACE 1100
Contact:

Re: How to synchronize your carburetors

Post by snowy.vtwin » Thu Jul 22, 2010 6:23 pm

I just checked out http://www.carbtune.com/ , the info and pricing there is best I've located. The 'Operation' menu selection on the left has a link to the Manual at the bottom of the page... after reading all this I ordered the thing, about $85 delivered with everything needed. Their restriction method insures equal flow thru all the tubes. After reading complaints of jumping gauges I was interested in the manometer type of gauge and this one seems very durable, serviceable, and non-toxic.

Trickster
Posts: 7
Joined: Sun May 30, 2010 12:34 pm
Location: Alberta, Canada
Motorcycle: 1978 GL1000
1979 CX500 C

Re: How to synchronize your carburetors

Post by Trickster » Fri Jul 23, 2010 10:51 am

Carbtune is the best I have experienced, worth the investment. Shipping took about 9 days from Ireland to Alberta, Canada.
Well packaged and fully intact.

Rick

flash771
Posts: 1
Joined: Sat Jul 03, 2010 3:12 pm
Location: Rathdrum, Idaho
Motorcycle: 1981 GL1000

Re: How to synchronize your carburetors

Post by flash771 » Sat Jul 24, 2010 10:44 am

great job on the post.
Thank you, now a trip to harbor frieght!
Dennis

Trickster
Posts: 7
Joined: Sun May 30, 2010 12:34 pm
Location: Alberta, Canada
Motorcycle: 1978 GL1000
1979 CX500 C

Re: How to synchronize your carburetors

Post by Trickster » Mon Aug 02, 2010 8:26 pm

Just did a buddy's 79 GL1000 with the "carbtune", wow was one cyclinder outta whack.

Absolutely amazing what a little synchronization will do to the way these bikes run.

I am impressed in how easy this "carbtune" is to use, and how it makes me look like I know what I am doing....lol

Rick

mooseye
Posts: 10
Joined: Sun May 23, 2010 10:10 pm
Location: Cleveland,TN
Motorcycle: 1990 GL1500 SE Red

Re: How to synchronize your carburetors

Post by mooseye » Mon Aug 02, 2010 10:00 pm

would you be interested in a little mail order rental?

User avatar
fishnquest
Posts: 8
Joined: Mon Aug 02, 2010 3:22 pm
Location: Ukiah, Ca
Motorcycle: 1981 GL1100

Re: How to synchronize your carburetors

Post by fishnquest » Tue Aug 03, 2010 12:37 pm

What an awesome thread. Thank you so much; makes working on the bike fun!

Kiwi_Roy
Posts: 3
Joined: Tue Sep 21, 2010 9:31 am
Location: Canada
Motorcycle: 1983 GL1100I

Re: How to synchronize your carburetors

Post by Kiwi_Roy » Sat Sep 25, 2010 6:12 am

I was looking all over for some 6mm adapters for my Guzzi, finally I hit on the idea of purchasing grease nipples. I ground the tip off the threaded end this let the spring and ball pop out making fine, cheap adapters. I doubt they are available in 5mm though.
I made my own sync tool using 1/4 tube with engine oil rather than water. The oil is nice and viscous which damps the pulsations out nicely. The easiest way to fill the tube with oil is just suck it out of the bottle. For the Goldwing I will simply add another U tube and connect the 2 together at the bottom,
Great article by the way

User avatar
nhegge
Posts: 47
Joined: Mon Jan 03, 2011 4:34 pm
Location: Anderson California
Motorcycle: 1982 ASPENCADE
1978 GL1000
1987 Rebel
1981 CM 400

Re: How to synchronize your carburetors

Post by nhegge » Tue Jan 04, 2011 4:11 am

Very helpful , never quite got the 2&4 connection before , now I do . Many thanks .


Be Nice 'til it's time to be Not Nice

Post Reply