How to synchronize your carburetors


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How to synchronize your carburetors

Postby WingAdmin » Mon Apr 06, 2009 9:19 pm



Synchronizing (or balancing) your carburetors is really a simple task, and is nowhere near as scary as it may sound. You don't have to have any knowledge of carburetors or how they work in order to do it. An annual springtime carb sync is a great way to keep your bike running smoothly, and perhaps improve your gas mileage while you're at it! Unfortunately, as the motorcycle is ridden carbs tend to go out of sync, so this is a procedure you should do as part of your regular annual maintenance, or more often if required.

Just what is a carb sync? On the 1100 Goldwing, as in a lot of motorcycles, there is one carburetor for each cylinder. Now when you have the throttle open, as you do when travelling at any sort of speed, they are set close enough to one another that their synchronization doesn't matter all that much.

However, at idle, or when you are just pulling away, and the engine is at low RPM, the throttle is virtually closed. At this point, tiny differences in synchronization make a big difference in engine smoothness.

Put it this way - if the throttle is 30% open, then a difference of +/-0.5% between different carbs isn't very noticible. However, if the throttle is 1% open, a difference of +/-0.5% makes a very big difference!

So synchronizing the carbs is just adjusting how "open" each carb is when the motorcycle is at idle. It won't make any difference at highway speeds, but you'll notice the increase in smoothness and reduction in vibration when tooling around town, or at stoplights.

The way this is done is to insert vacuum gauges in the intake manifold. The engine is trying to suck fuel and air into it, to combust. The throttles are closed (mostly), preventing this fuel and air from getting to the engine. The result is a vacuum, and this is what we are going to measure. The idea is to get the amount of vacuum the same in all four intake manifolds. When we've done this, we know the carbs are synchronized (balanced).

1. You will need some vacuum gauges. I bought a set of four from Harbor Freight for around $9 apiece, when they were on sale. They are reasonably accurate, and good enough for this job. You can get away with two, or even one, but four (one for each cylinder) makes the job much easier.

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2. You will need some aquarium valves, from your local pet store. The problem with reading the vacuum from the intake manifold is that there is a pulse of vacuum when the intake valve opens and the piston moves downward, sucking fuel and air into it. When the intake valve closes, the vacuum drops. Reading this is impossible, because the needle on the vacuum gauge will flick back and forth as the valve opens and closes. The solution is an aquarium valve. The valve is inserted in the line in between the intake manifold and the vacuum gauge. It restricts the volume of air that can go back and forth through the tube, damping the needle oscillations.

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3. Cut the hose for each vacuum gauge about 3 inches from the end, and insert the aquarium valve in place. I used superglue to make sure they would stay in place.

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4. The last thing you will need is some intake adapters. The 1100 requires 5mm adapters, other Goldwings require 6mm adapters.

Update: The same adapters have been found online for $10 less: http://www.powersportsuperstore.com/Mot ... 451996.htm

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5. The hoses from each gauge will be hooking into the intake manifolds on each of the four cylinders as shown. Note the cylinder numbers, from 1 to 4.

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6. Using a philips screwdriver, remove the intake manifold plug from each cylinder.

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7. Carefully screw in the adapter in place of the plug on each cylinder. Tighten them by hand, so that the rubber O-ring is compressed, sealing the connection.

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8. Connect each hose between the adapters and the vacuum gauges, making sure the aquarium valve is closest to the adapter. The larger volume of air in the hose in between the valve and the gauge acts as a damper.

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9. When all the gauges are connected, they should be at zero (or close to it).

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10. While not necessary, you will find it much easier to make the adjustments on the carburetors if the chrome carburetor guards on each side are removed. Remove the four screws from each guard.

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11. Gently remove the spark plug wires from the plastic stay, and remove each guard.

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12. The adjustment screws are hidden down next to each carburetor - except for #3. Carburetor #3 is the baseline carburetor, and has no adjustment.

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13. Each screw has a slotted head, and an 8mm locknut holding it in place, so that vibration won't change the setting during normal operation.

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14. When making adjustments, hold the screw in place with a slotted screwdriver, while loosening the locknut with an 8mm wrench. Then make the adjustment to the screw. Finally, while holding the screw's new position, retighten the locknut. Loosening the screw (counterclockwise) increases the vacuum, and tightening the screw decreases the vacuum.

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15. Set up a large fan to blow over the radiator for this procedure. The engine needs to be at operating temperature, and we don't want it to overheat. Additionally, we want to prevent the radiator fan from cycling on and off if at all possible, as this can alter the idle speed of the engine, and change the vacuum readings.

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16. Start the motorcycle and allow it to warm up normally. The engine should be at normal operating temperature, with the choke off, and should be idling at normal idle speed (approximately 950 rpm) before starting the carb sync procedure.

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17. Adjust each valve so that there is a slight amount of needle movement on each meter. If there is no movement at all, there is a chance that the valve has closed, or is restricting so much air that it is not allowing the full vacuum through, and is distorting the reading. As long as the needles are moving somewhat, we know the valves are open enough to let through a valid amount of vacuum, and the reading is valid.



(This is a video - click Play to watch)


18. Next, get an error reading on each vacuum meter. Chances are your meters will not be reading exactly the same, especially if you are using inexpensive meters! To start, connect the hose from cylinder #3 to the first meter, and note the reading. This is your baseline. Connect the hose to the second meter, and note the reading. This is the amount of error for that meter. If the reading is higher or lower than the first meter, then note this - I like to simply write above the meter "+0.5" (meter reads 0.5 low, so this tells me to add 0.5 for any measurement taken on this meter) or "-0.75" (meter reads 0.75 high, so this tells me to subtract 0.75 from any measurement taken on this meter) etc, as a reminder. Continue with the third and fourth. Now that you know how each meter reads in comparison to the first one, we can make accurate measurements by adding or subtracting from the indicated measurements the amount of error on each meter.

If you are using only one meter, you can skip this step, of course!

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19. Now that we have calibrated our meters, it's time to start the carb sync. Make sure the engine is idling properly, and read the vacuum level on carburetor #3. This is our baseline. Next, read the vacuum level on carburetor #1. If the vacuum level on carburetor #1 is not the same as the reading for carburetor #3, then adjust the sync adjuster on carburetor #1 so that it does match. The adjuster for carburetor #1 is located between carburetor #1 and carburetor #3. This takes a little bit of practice, as it is quite sensitive.

Once you have carburetor #1 and carburetor #3 balanced, adjust carburetor #2 to match carburetor #4. The carburetor #2 sync adjuster is located between carburetor #2 and carburetor #4. Don't worry about making carburetor #2 match carburetor #1 or carburetor #3 at this point, just make sure carburetor #2 is set to match carburetor #4.

Once carburetor #2 and carburetor #4 match, adjust carburetor #4 to match carburetor #3 - essentially at this point you are balancing the left cylinders against the right cylinders. The adjuster for carburetor #4 is located just to the rear of it.

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20. When you are finished adjusting all the carburetors to your satisfaction, shut the bike off and allow it to cool - you don't want to burn your fingers removing the adapters! Remove the hoses from the adapters and put the vacuum gauges away. Once cool, remove the adapters.

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21. Replace the intake plugs, and ensure that they are not cross-threaded before tightening.

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22. Replace the carburetor guards, and gently squeeze the plug wires back into their stays.

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Enjoy the smoothness of your freshly synchronized engine!



miille1
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Re: How to synchronize your carburetors

Postby miille1 » Fri Jun 26, 2009 12:29 am

Great job on the video. Thanks for takeing all that time to show us non mecanics how its done Jimmyman1

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Re: How to synchronize your carburetors

Postby kyace » Fri Jul 24, 2009 2:56 pm

what about the 1500 carbs? any help there.

thanks ron

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Re: How to synchronize your carburetors

Postby WingAdmin » Fri Jul 24, 2009 3:13 pm

I don't have one to take pictures of, but it's even easier than the 1100 - it has only two carbs, one for each bank of cylinders, and the left side is fixed - you sync the right carb to the left carb. Have a look at the 1500 Service Manual on the manuals page, in the maintenance section it has details and pictures on the procedure.

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Re: How to synchronize your carburetors

Postby giffen49 » Fri Aug 21, 2009 8:42 am

Thanks for all the time and effort you have put into these DIY solutions. I have begun to build my vacuum Sync. tool for my 1983 GL1100A Aspencade but I am having a problem locating the 5mm adapters. The link you supplied says they are not available. Any other suggestions or sources?

Thanks again.

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Re: How to synchronize your carburetors

Postby WingAdmin » Mon Aug 24, 2009 12:40 pm

Sad they don't offer it anymore. Here's a place that sells similar items.

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Re: How to synchronize your carburetors

Postby giffen49 » Thu Aug 27, 2009 11:50 am

Thanks a lot. I looked on the Motion Pro web page and found a dealer in town. Total cost for a set of 4 was $16.00 Cdn.

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Re: How to synchronize your carburetors

Postby tumunga » Wed Sep 16, 2009 9:39 pm

Thanks for the instructions sir. Worked like a charm!
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Re: How to synchronize your carburetors

Postby BigWingD » Thu Oct 01, 2009 9:38 pm

Great Job Can you tell me what size fitting the gl1000 use the 5mm or 6mm.Thanks in advance.

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Re: How to synchronize your carburetors

Postby knoxy » Wed Dec 09, 2009 4:09 am

giffen49 wrote:Thanks for all the time and effort you have put into these DIY solutions. I have begun to build my vacuum Sync. tool for my 1983 GL1100A Aspencade but I am having a problem locating the 5mm adapters. The link you supplied says they are not available. Any other suggestions or sources?

Thanks again.

i found that plastic fitting from garden irrigation kits have 5mm thread and seal up nicely even without the "o" ring. They look similar to the correct adaptor.

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Re: How to synchronize your carburetors

Postby robertdawber » Wed Mar 24, 2010 9:31 pm

Could you do this one at a time using the gauge from the Mity Vac?

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Re: How to synchronize your carburetors

Postby WingAdmin » Wed Mar 24, 2010 9:40 pm

You can do it one at a time using a vacuum gauge (and this is a good way to ensure they're all done the same, because the gauges don't have to be calibrated - you're using the same one each time) - but I kind of doubt the Mity Vac gauge has the resolution or accuracy required to sync them properly.

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Re: How to synchronize your carburetors

Postby robertdawber » Sun Apr 18, 2010 8:46 pm

This is one of my next steps-
One question-I have plug guards on and wonder if any others have a solution to air seepage from the extra items on that screw?
in other words-using a longer screw with a seal washer or using thread sealant?
Bob

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Re: How to synchronize your carburetors

Postby Jeeper » Mon Apr 19, 2010 5:12 pm

I'm confused about one point you mentioned. As each of the carbs are adjusted individually, with the exception of #3, how is it that adjusting #2 to match #4, then adjusting #4 to match number #3 doesn't throw #2 back out of adjustment? Wouldn't you want to adjust each one to #3?

I checked the service manual but it just states to make sure all the gauges are within 50mm of each other, "adjust as necessary".

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Re: How to synchronize your carburetors

Postby tumunga » Mon Apr 19, 2010 6:09 pm

Jeeper wrote:I'm confused about one point you mentioned. As each of the carbs are adjusted individually, with the exception of #3, how is it that adjusting #2 to match #4, then adjusting #4 to match number #3 doesn't throw #2 back out of adjustment? Wouldn't you want to adjust each one to #3?



All that adjustin' is hard to get my head around, but it's pretty simple. You adjust carb #2 to carb #4, which are on the same side of the bike. After you've done that, they are synched to each other, so they now work in unison, just like carb #1 and carb #3 on the other side. Any adjustment you now make to carb #4 will also adjust carb #2 the same amount because they work as a pair. When you adjust #4 to #3, you are really adjusting carbs #4 AND #2 to carb #3, because #4 and #2 work in unison.

I hope that helped.
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Re: How to synchronize your carburetors

Postby robertdawber » Thu Apr 29, 2010 8:12 pm

Anyone find VACUUM ADAPTERS local? Any ideas?
Bob

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Re: How to synchronize your carburetors

Postby WingAdmin » Fri Apr 30, 2010 9:12 am

You can order them direct from Motion Pro online. Their adapters are intended to be installed permanently, and have rubber cabs that install when you are not doing synchronizing.

I am going to need to sync my carbs again soon, I need to figure out where I left my adapters!

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Re: How to synchronize your carburetors

Postby canal mark » Sat May 01, 2010 10:48 am

Just finished sync'ing my carbs and thought I would share some experiences. First of all...if you get the 5MM adapters that are brass and extend out with a 2" - 4" tube, be very careful handling these thing when screwing and unscrewing them, or pulling off the tubing! They break very easily :evil: Second...I could not find the little air restriction valves anywhere, so I made my own. A pair of vice grips clamping the tubing in just the right spot does the trick :o . My problem now is trying to fix the little carb backfire problem I still have after rebuild and sync. I have half a can of Seafoam still in the tank, so I thought I would run this out before messing with it anymore. Other than the the little bit of backfire on the carbs of my 1980, it is running GREAT! I got the bike for $200 not running and one month later I am cruising and smiling :lol:

Update...The Seafoam has been run out and fresh gas added. WOW :D she is one SWEET running bike. I did not use the expensive rebuid kits, but rather, the $10 kits from the "other" supplier. Everything I needed was in there and I saved $130 :D :D .
Last edited by canal mark on Thu May 06, 2010 12:42 pm, edited 1 time in total.

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Re: How to synchronize your carburetors

Postby stuhrdw » Sat May 01, 2010 4:08 pm

I just hooked the Mercury gauge up to all four cylinders, they all drew a vacuum except cylinder 4, it blew into the tube. I have spark at that wire as I disconnected it and spark arced from the wire to the plug connection.

What the heck, any ideas? hope it is not serious.

Thanks

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Re: How to synchronize your carburetors

Postby WingAdmin » Sat May 01, 2010 7:34 pm

If it's blowing instead of sucking, you've got valve problems. Either a stuck valve, or something causing it to be otherwise open when it shouldn't be, i.e. cam or timing. First thing to do is check the compression.

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Re: How to synchronize your carburetors

Postby stuhrdw » Sat May 01, 2010 8:49 pm

Thanks for your reply, i will check that, I need to get a gauge. I will let you know.

DWS

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Re: How to synchronize your carburetors

Postby stuhrdw » Sun May 02, 2010 5:52 pm

Compression is pretty much non existent in that cylinder (4). I bought a gauge, but it did not have the correct adapter. I checked it with my finger and as compared to the other cylinders it barely puffed any air.

I am restoring this goldwing. I changed the timing belts, but carefully marked the crank and cams with a white paint line and carefully put everything back as it was before I removed the old belts. They could have slipped before on the old belts though.

I am going to adjust the valves as per Clymer. Hope it works

DWS

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Re: How to synchronize your carburetors

Postby robertdawber » Sun May 02, 2010 7:58 pm

Keep us updated-
Bob

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Re: How to synchronize your carburetors

Postby jackknife » Wed May 05, 2010 11:24 am

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. ;-)

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Re: How to synchronize your carburetors

Postby WingAdmin » Wed May 05, 2010 11:30 am

Not so great though if you suck the water into your carbs. :)




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