'How to' Balance / Synchronize your Carburetors

##I have decided to do a write-up on how to synchronize the carburetors. This is the first draft. Pictures will be added in coming days. Any comments or steps people want to add will be welcomed. I also believe this thread will make redundant some of the other half complete threads on the topic. I have done this to eliminate any confusion from what is a fairly straight forward process.##

##UPDATE: Pics added. Still looking for some feedback fellas. If you have anything to add or want something explained better, now would be the time.##

Notes:
The model being used in the tutorial is the 3ln3 but I am certain the 3ln1 or 2kr wouldn’t be too dissimilar.

How do you know if your bike needs its carburettors synchronized?
You can usually tell by looking closely at the tachometer needle. Try holding the throttle to sit on say 4000 revs. The needle should be able to sit almost dead still on the 4000 mark, if you find the needle moves up and down without changing throttle input they need to be balanced. Also if you don’t know when it was last done or you have just cleaned or adjusted the carburetors it is a good idea.

Equipment needed;
-Set of vacuum gauges. I have used the carbtune vacuum gauge (manometer). You can get other types of vacuum gauges but do yourself a favour and get one of the non mercury versions available. You can find info on the carbtune here. <!-- m --><a class="postlink" href="http://www.carbtune.com/">http://www.carbtune.com/</a><!-- m --> Most motorcycle accessory shops will be able to sell you something or point you in the right direction.
-Socket set (metric)
-Set of allan keys (metric)
-Assorted Screw drivers
-Old rags or a jar
-10mm ring spanner
-Beer

Disassembly

Step 1: Remove the front side fairings.

Step 2: Open the pillion seat and remove the small plastic fairing at the rear of the rider’s seat.

Step 3: remove the bolt holding the riders seat.

Step 4: Remove the six screws holding on the rear fairings. Four are located under the pillion seat and another two below the rear break light.

Step 5: Making sure no to break the brittle plastic spigots pull the front of the rear fairings away from the bike, they should just pop out. At this point the fairings should come away from the bike. There is no need to remove the rear brake light and surround.


(I really need to wash that bike)

Step 6: Make sure the fuel tap is in the off position. Remove the lower most hose from the tap. It’s a good idea to have a rag or jar handy as fuel will spill from the line. It should stop after a few seconds.



Step 7: Remove the two screws that hold the fuel tap to its bracket. Push the fuel tap in on top of the gearbox so it is clear from the frame or any other obstructions.

Step 8: remove the bolt and the allen screw holding the fuel tank to its mounting points at the top front and rear base of the tank.



Step 9: Find something to place the fuel tank on once it has been removed from the bike. A plastic milk crate or empty beer carton with a hole cut in the side will do the job. Remove the tank by lifting it vertically being careful not to snag the fuel tap or vent pipe.



Step 10: Remove the airbox from the carburettors making sure to disconnect the drain tube and the vent pipes from carburettors. You will have to loosen the clamps that hold the airbox to the top of the carburettors.


(Photo one shows the vent and drain pipes that need to be detached from the airbox. Photo two shows the clamps that need to be loosened before the airbox can be lifted from the carburetors.)

Synchronization

Step 11: Place the fuel tank next to the bike and reconnect it to the hose you removed from it earlier. You may be able to balance the tank pointing backwards where the rider sits or stack crates next to the bike to prop the tank on, use your imagination. Turn the fuel tap on.

Step 11: If not already warm, start up the bike and let it get up to operating temperature then turn the bike off.

Step 12: Remove the four allen screws in the intake manifolds. In their place, screw in the adaptors that came with your vacuum gauge making sure the thread is the right size. Do not over tighten the adaptors, they are sealed with an o ring and will leak if too tight. Attach the rubber vacuum hoses over the adaptors to the vacuum gauge making sure not to cross the lines i.e. Carb one to gauge one, carb two to gage two etc.


(Photo one shows the location of the four allan head screws that need to be removed and replaced with the adaptors. Only the first two are visible but you get the point. Photo two shows how it should look with the hoses and adapters in place, the carburetors have only been removed to get a decent photo, there is no need for you to remove them.)

Step 13: Start the bike up and blip the throttle and let the revs settle. What you want to do is have all the gauges reading the same vacuum pressure. Chances are they will be a bit off. To bring the readings closer together you will need to turn the adjuster screws.


(The first picture is from above and the second from below the carburetors. Circled in blue are the butterfly linkage adjuster screws referred to in step 13. The first shows the adjuster screw for carbs 2 and 3 from above. The second shows all three adjuster screws viewed from beneath the carbs. The only reason the carbs where removed was to get a good photo of the screws, they can be adjusted while the carbs are on the bike.)

The FZR has four carburetors; to adjust them you should balance 1 and 2, 3 and 4, then 2 and 3. They don’t have to be perfect just as long as they are within about 1 or 2mm of each other. After each adjustment blip the throttle to reset the gauges. Note: keep an eye on the temperature gauge! If it gets too high turn the bike off and let it cool. A pedestal fan can help in this situation.


(This photo shows the view of the gauge the first time I synchronized my carburetors. As you can see cylinder one and two needed a bit of a tweaking, 3 and four needed a lot more tweaking and then the middle screw needed to be turned to bring 1,2 and 3,4 together. Advice to all the noobs out their! This was AFTER the bike had been taken to one of the larger workshops in town for a major service. Don’t trust that a mechanic has done something just because it appears on the bill. The sooner you learn this lesson the better.)

Step 14: Once you have the readings all the same you are half done. Remove the fuel tank, gauge hoses and adapters and replace them with the original allen screws. Be careful of the cooling pipe at the back of the engine, it is extremely hot and unless you have the hands of a small Japanese boy you will probably burn yourself if not careful.

Reassembly

Step 15: Repeat steps 10 to 1 in reverse.

Step 16: Take the bike for a test ride.

Step 17: Drink beer.

Mythbusting

Myth – You can balance your carburetors with ball bearings.
Explanation

 

woah! Awesome post ciaran!

 

Ok, I went to do this yesterday, but got stuck on the very first part: buying a vacuum guage. Couldn't find one at Autobahn, Supercheap, or repco. Not even in their product catalogues. Ahh well, might have to order one online through carbtune, or go down to the MC shop (they weren't open yesterday, being a sunday and all).

 

bugger me, they're not cheap, are they?
Au$160 to get it delivered.

ah well, i'm sure I'll get good use out of them.
*sighs and procedes with the order*

 

You should have given me a heads up and I could have lent my one to ya.

You can get cheaper dial type ones but the carbtune is one of the best non mercury gauges around. I have a number here somewhere for someone who sells the dial type if anyone wants it.

 

I was considering asking for a loan
But Leah's bike needs a tune up anyway, and it says it works for some fuel injected vehicles too... so I can see myself getting a bit of use out of them.

Incidentally, would I be able to book you in sometime to walk me through checking valve clearances? I'm not 100% on what needs to be done, and considering the fluctuations everyone seems to report when they first check them, I'd like to do them myself.

 

Great post! Finally good to get a decent write up.
I have only one whinge about the entire how-to, you removed the airbox!
Any and all tuning done to the bike, especially in regards to air flow on the intake side needs to be done with the bike in running spec. Removing the airbox will vary the way the air enters the carbs and as such you'll end up with different (even only slightly) results if you balance carbs without the airbox on.

From me perspective, i'd highly recommend people leave the airbox on when balancing the carbs, unless your having a darn impossible job of finding the balance screws. Even still, better take longer and get a flashlight in there.

 

I have had that thought before and looked into the effect it had. I balanced the carbs as above, left the vacuum hoses on the manifolds and put the airbox on. The difference it made wasn’t worth the amount of f*&#ing around IMO. If you had a funky custom or homebrewed air filter and or airbox test it out first tho.

I would guess this would be more critical on a larger bike with the increased amount of flow through the airbox.

 

To tell you the truth I haven’t checked the one on the fizzer myself before. I did do it on the GS tho. Hardest part is finding a set of feeler gauges with small enough fins. The smaller clearance fins on my dads ancient set have well and truly past it.

I think I have a table somewhere to help work out required shim sizes. I will see if I can dig it up.

 

aight, i'll check my feeler gauge set to see how small it goes. i think it's in pretty good nick...

 

If I can get a look at your table that would be grate .

 

Sure, you want the correct thickness, but the issue here is width.

 

I haven't even looked at the valves before, so I wouldn't know... Please elaborate?

 

The main problem with feeler gauges is the width of each of the pieces. Most of them come in about 1.5cm widths and that won't fit in alot of bikes. The ones Yamaha sell are about 6mm in width and do the job perfectly... but at $37 for 4 gauges it's a teency bit expensive.

I actually managed to get mine done with a bit of a clean chop job on one of the cheapo larger sets then just made sure i didnt put the bit i cut underneath the cam lobe. Worked quite well once i got the hang of it!

 

I never had that problem on the GS, but granted it only has one intake and one exhaust valve for each 250c c cylinder.

The clearance spec was as small as 0.03~0.08mm (intake and exhaust) though. I seems strange because when I tried to find the ones for the FZR they where as large as "1. 4 - 8 thou (.1-.2mm) for inlets and 8 - 12 thou (.2-.3mm) for exhaust."

Is this right?

Oh and I found the table but it is geared towards finding results for the 0.03~0.08mm so I don’t know how useful it would be.

 

Yep, those specs are right for the FZR (or atleast they're right for the 1000).
I wonder why the GS has such small clearances.

 

It is a bit strange. They came out of the workshop manual and it was the seconded by a reputable Suzuki mechanic. Plus it seems to run like a champ.

 

can't wait for step 17 <!-- s:alcoholic: --><img src="{SMILIES_PATH}/icon_all_coholic.gif" alt=":alcoholic:" title="Alcoholic" /><!-- s:alcoholic: -->

 

Do you balance the carbs with the airbox on or off? I'm about to mine.
Cheers.

 

Normally done as the bike would be set up to ride - airbox on.