"advanced" Throttle Body Synchronization

[FJRocha]

A while back I saw an article or posting on how to do an "advanced" Throttle Body Synchronization. It talked about doing the sync at 4krpm in addition to the idle speed. I seem to have misplaced the link, has anyone seen it laying around somewhere?

 

[fjrinbc]

I have not seen the article you are referring to, but this 'advanced' throttle sync would be to adjust the positions of the throttle plates relative to each so that they all open equally and each cylinder produces the same amount of power. The 'normal' vacuum sync would have little to no effect at 4000 rpm or higher, as it uses a small passageway around the throttle valve and is for idle and low rpm smoothness.

It is entirely possible to do this adjustment and is probably a worthwhile thing to do. It can be time consuming. Anyone who used to own an older 4 cylinder bike and liked to do their own work has most probably done this to the carburetors.

For the record Yamaha recommends you do not touch this, but that should not stop you from trying. They put the ability to adjust in there for a reason, right? If you do go ahead and do it you will have to reset the idle vacuum sync, but I am sure you know this.

Len

 

[FJRocha]

I did my first sync today (@800 miles). And for the life of me, I could not reach the 250mm mark. The screws reached bottom at 230mm. So I adjusted them all at 230mm. I am in Chandler, AZ, which is at about 1100' above sea level, is there a compensation factor for the elevation?

 

[fjrinbc]

FJRocha

You did the right thing. It is more important to get them even than to spec. Is your idle speed at the proper rpm? That can affect things.

Are you using the proper weight and type of oil?

Just kidding, I love the oil threads.

Len

 

[FatNakedGuy]

FJRochaYou did the right thing. It is more important to get them even than to spec. Is your idle speed at the proper rpm? That can affect things.

Are you using the proper weight and type of oil?

Just kidding, I love the oil threads.

Len

My idle knob stopped working the last time I sync'ed the tbs. Any idea why? Thanks!

 

[jdeez1]

I alos could not get to the spec. Chicago about 950 ft elevation. So I did as you and just settled for a different number.

 

[Ramblin Man]

Did you remember to put the little rubber caps back on?

Here is the method to adjust the throttle bodies at 4K rpm.

First get a big fan and put it in front of the bike to help cool it while you do this because it can take some time.

tank raised

manometer attached

air injection hose disconnected and pluged

start the bike and let it reach two bars.

Using a throttle lock or an assistant, set your rpm to 4K with the throttle and hold it there. Observe your vaccuum readings. if they are the same or very close you are done.

If they are different, locate the throttle linkage adjutment screws. There are three. One adjusts 1 to 2, another adjusts 3 to 4, and the other adjusts 1-2 to 3-4. They are easy to see. good size screws with springs....

The idea here is to get 1 equal to 2 . then get 3 equal to 4 , then adjust 1-2 to 3-4 so they are all the same.

My suggestion is to do this at the RPM that buzzes above 4k. My bike was smooth right at 4k but by 4300 it was pretty buzzy. So decide where you really want it smothed out and do it there because it will probably be worse there than at 4K.

Once you move the plates you need to redo the idle sync and then recheck the 4k values. You may need to do a few rounds to get it just right.

Remember to SLOWLY close the throttle because vacuum raises on decel.

 

[teerex51]

Good write-up Ramblin, thanks!

Stef

 

[MCML]

I could not reach the 250mm mark

In addtion to altitude issues, if you are using a mercury filled device to measure the vacuum, the reading might depend on how much mercury was in the "stick"

 

[Showbart]

In my only sync, #1 bottomed out while syncing it to #3. Is #3 not ever to be adjusted at all?

Also, the manual for my econo Motion Pro Carbtune warned against revving over 3500 as the mercury might be sucked into the cylinders.

 

[markjenn]

You get a feel for how much throttle jockeying you can do before the mercury raises dangerously. You really have to be ham-fisted to get it to sucked into the engine.

My manometers have developed small air pockets in the mercury columns which are undoubtedly affecting the accuracy, so I just got a Morgan Carbtune which has no mercury - haven't used it yet though.

The principle here is pretty straightforward. At large throttle openings, the sync of the butterflies predominates and Yamaha feels that this is something that is set at the factory and never requires adjustment. The air screws that you are supposed to adjust add a small amount of bleed air to trim the sync at small throttle openings where even a tiny bit of mis-sync might cause a ragged idle.

At idle, each cylinder is getting some air from the air screws and some from the idle adjustment knob which is raising all the butterflies off their stops. If the idle knob no longer works, it means that the air screws are supplying too much air and are controlling idle. Conversely, if you bottom out an air screw trying to get it to match #3, you should make sure you're idling at spec and possibly crank up #3 a bit so you're not so low in the adjustmet range.

Many have said that the 250mm reading is bogus. Instead, you should be looking for #3 to be about 1/2 turn out from bottoming and then you'll have about the right proportion between the air screws and the idle adjustment knob.

I was able to get everything pretty close by just fiddling with the air screws, but now that I have the Morgan, I'm going to do it again and see how close things look at 4K or so.

My experience with this stuff is that you can chase it if you get too anal. Sync helps the vibe problems but beyond a certain point, you're tilting at windmills.

Best regards,

- Mark

 

[FJRocha]

I did notice a jump of the mercury when letting go on the throttle, but it didn't go to the top of the tubes. Another thing I just though of is that I didn’t open the vent in the mercury deposit, although minimum, this could create a vacuum in the container that would fight the rise of the mercury.

At iddle, the mercury was a bit jumpy, but at the same level (230mm), and at 4k the mercury was stable, but out of sync (about 20 to 30mm out); I didn't screw with the screws because I didn't know any better and din't want to mess it up. I'll probably get to it next time, but first I need to identify the resonance frequency or "rattling rpm" of my bike. I also need to use more finesse when bringing it to 4k because the engine is unloaded and very touchy in neutral. <_<

 

[skyway]

Copyright 2004 Arlen Bloom

The Unauthorized Throttle Body Synchronization Procedure

There has been a lot of interest in the Throttle Body Synchronization Procedure lately, with a new generation of Waiters finally taking delivery of their 2005 FJR’s, so I thought it timely to discuss the procedure recommended in the service manual as well as another I used to synchronize the bike at highway speeds as well as at idle.

My motivation for seeking an alternative procedure came when I found all four throttle bodies synced at idle, and all but one synced at 4200 rpm. Many FJR owners complain of excessive vibration or buzz in the handlebars between 4000 and 4500 rpm and I thought synchronization at an engine speed we spend more run time at might eliminate a good portion of that. The service manual only illustrates syncing at idle, but in theory, everything should also work in unison at 4200 rpm. To confuse things more, the manual also says to NOT adjust the butterfly adjusting screws and does not include any information on how the throttle body assembly actually works. In fact, if you need to replace certain throttle body parts, the parts diagrams indicate you would have to order a complete throttle body assembly! I decided it was time to unravel some of the mystery about throttle body adjustments.

So How Does the Throttle Body Assembly Work?

The purpose of the throttle body assembly is to mix fuel and air and introduce that mixture to the combustion chambers via the cylinder head. It is important for the airflow in all throttle bodies to be equal so that each cylinder carries its share of the load and does not create an engine that runs rough, hot, or too rich or lean. Equalizing the airflow is accomplished by performing the synchronization procedure.

Carburetors mix airflow with fuel, but throttle bodies only control airflow. While carburetors use slides to change airflow above idle, throttle bodies use butterfly valves. At idle, airflow is to be adjusted with air screws.

The FJR uses its #3 throttle body as a baseline to which the other throttle bodies are synced. In addition to the air screws, synchronization is affected by:

1. the initial vacuum setting of the #3 throttle body

2. the mechanical adjustments between throttle bodies

3. idle speed

4. interference of idle speed by throttle stop screw adjustment or throttle cable adjustment

5. any vacuum leaks between the air box and the throttle bodies, or between the throttle bodies and the cylinder head

Throttle stop screws are adjusted to set the minimum idle speed that can be achieved by turning the idle adjustment screw. Butterfly sync screws adjust the butterfly openings of adjacent throttle bodies so they have the same amounts of airflow at a given engine speed above idle. Air screws bleed off a small amount of vacuum to adjust the amount of airflow to equal that of throttle body #3 at idle.

Synchronization By-the-Book

Let’s start with the synchronization procedure that everyone has been doing up to now. The steps are modified a bit to tie it all in with the Unauthorized Synchronization covered later. You will need a long, thin-bladed screwdriver to adjust the air screws, a vacuum gauge, and a carburetor synchronization tool. I use a TwinMax electronic meter, but a mercury stick or Morgan Carbtune will allow you to look at the vacuum readings of all four throttle bodies at once and eliminate a lot of hose-switching between adjustments.

After warming your engine up to at least two bars on your bike’s graphic display (while avoiding exposure to carbon monoxide) and raising the gas tank to access the throttle body area, follow these steps:

• Adjust the idle speed to 1000 rpm using the idle adjusting screw found on the right side of your bike. This would be just inside your right knee if you were sitting on your bike.

• Find the appropriate vacuum port for throttle body #3 and remove the little rubber cap. Connect the vacuum gauge hose to the vacuum port and place the gauge where you can easily read it while making adjustments to the #3 air screw.

• Adjust the #3 air screw until you read 9.8” Hg (+ 1” Hg per 1000 ft. above sea level). You may need to restrict the vacuum hose to keep the needle from jumping around. Check your idle speed again and readjust until both adjustments are attained simultaneously.

• Remove the vacuum gauge hose and attach the carburetor synchronization tool to vacuum port #3 and one of the other vacuum ports. (All three if you are using a 4-hose tool.) Note which hose is connected to #3.

• Turn the air screw(s) to adjust the vacuum at each throttle body to match that of #3. All four throttle bodies should be within .4” Hg. Check your idle speed again after adjusting each air screw and readjust vacuum and idle adjustments until both are attained simultaneously.

• With the hoses still attached, use your throttle to increase engine speed to 4200 rpm and see if your gauge still indicates synchronization. If they all look good, you do not need to go any further. Otherwise, you may want to perform the Unauthorized Synchronization Procedure.

Synchronization Without Authorization

I have given this procedure a rather ominous name because I want to impress upon you that this is serious business. As it is not covered by the Yamaha service manual, this is uncharted territory (until now anyway) and if you are all thumbs when it comes to mechanics, you should put down your tools and step away from your bike. This method of synchronization is one that must be done meticulously and from the first step through the last. Having a brain fart or nervous breakdown in the middle of it is not acceptable! If you were to screw up the idle speed synchronization in the previous section, it is no big deal. Your bike will still start and run and you may not even realize you screwed it up. But if you screw THIS up, you WILL know it. Chances are real good your idle speed will not adjust to lower than 1300 rpm. And it goes down hill from there! If you do this procedure, it is YOUR decision and YOU suffer the consequences! I take NO responsibility for YOUR actions!

You still with me? Good. I just have to make it sound scary to chase off those who shouldn’t even be reading this, let alone jumping in with a screwdriver. Be aware, however, that we will be messing with painted screws and it is uncertain whether they were painted to keep them from turning or to indicate when some idiot messes with them. My logic is that Yamaha doesn’t plan on doing anything warranty-related with throttle body adjustments, but if they aren’t in sync at the speed you normally ride, it is required that something be adjusted. So come on lemmings! The cliff is this way!

In addition to the tools you used for the idle speed synchronization you will need a cross-tip screwdriver, 8mm combination wrench, and a 2.5mm hex wrench. Make sure your idle speed sync has been done with reasonable success, and your gas tank is raised for access to the throttle body area. This may take some time, so consider pointing a fan at the front of your bike to help keep it from melting. And don’t expose yourself to a carbon monoxide poisoning situation! Now follow these steps:

• Adjust your throttle cable at the grip so there is a small amount of slack. We don’t want the cable to interfere with our idle speed when we are making critical adjustments.

• Back off the idle adjustment screw until idle speed quits dropping. This will show us the minimum idle speed and it should be about 750 rpm. Don’t get carried away, if you go too far the screw will fall out and you will be on your own.

• Look at the painted throttle stop adjustments. These are the pairs of small hex socket set screws with lock nuts located between throttle bodies #1 & #2 and #3 & #4. The levers connected to the butterfly valves bump up against these stops at their minimum opening. All four levers should touch their stops at the same time and the idle speed should be 750 rpm. Close any gaps by adjusting each stop screw until it just touches the lever. If idle speed is above 750 rpm, you will probably see a gap between one or more of the levers and their stop indicating a throttle body is out of sync. Back off each of the four stop screws by small amounts until idle speed drops to 750 rpm. If idle speed is below 750 rpm, adjust the stop screws to increase the idle. Adjust them by loosening their lock nuts and using the hex wrench to turn the screws then tighten the lock nuts. To gain enough clearance for my combination wrench, I removed the two screws for the fuel rail and took out the aluminum standoffs. Grinding a flat spot on each standoff allowed me to get my wrench over the lock nuts. Next time, this won’t be a problem. Be careful not to cut the little injector O-rings when reinstalling the fuel rail.

• Boost the idle speed back up to 1000 rpm using the idle adjustment screw. This idle speed is very important and should be maintained after any other adjustment is made. Make an adjustment, readjust your idle speed, then check the new adjustment again until the adjustment and the idle speed are both where they should be. This applies to every step throughout the entire procedure from this point on.

• Adjust the vacuum on throttle body #3 for 9.8” Hg (+ 1” Hg per 1000 ft. above sea level) using the #3 air screw. This screw should not be touched again! Throttle body #3 is our reference point and we have just set the base line. Leave it alone from this point on! Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment.

• With your carb sync tool attached and throttle speed increased to 4200 rpm, adjust the butterfly sync screw between throttle bodies #3 & #4 until the vacuum on #4 equals that of #3. These painted screws have cross-tip heads and springs on the shafts. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment. Also make sure the throttle stops do not touch the butterfly valve levers.

• Sync throttle body #4 to throttle body #3 at idle by adjusting the #4 air screw. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment.

• Compare the vacuum of throttle body #1 to the vacuum of throttle body #2 at 4200 rpm and adjust the butterfly sync screw between them to make the vacuums equal. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment and make sure the throttle stops do not touch the butterfly valve levers.

• Sync throttle body #1 to throttle body #3 at idle by adjusting the #1 air screw. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment.

• Sync throttle body #2 to throttle body #3 at idle by adjusting the #2 air screw. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment.

• Sync throttle bodies #1 & #2 to throttle bodies #3 & #4 at 4200 rpm by adjusting the butterfly sync screw between throttle bodies #2 and #3. To make this adjustment, you will have to shut off the motor and twist the throttle grip until the butterfly sync screw is accessible with your screwdriver. It will probably take you about three repetitions to make the adjustment. Use the idle adjust screw to make sure your idle speed is 1000 rpm throughout this adjustment and make sure the throttle stops do not touch the butterfly valve levers.

• Sync throttle bodies #1, #2, & #4 to throttle body #3 at idle by adjusting the respective air screws. Make adjustments to the idle adjust screw after each air screw adjustment to ensure that idle speed remains at 1000 rpm.

• Compare the vacuum readings of all four throttle bodies at 4200 rpm to see if they are within .4” Hg of each other. If they are, your throttle bodies are now completely synchronized and you are finished. If not, go back to the beginning of this section and perform the procedure again. It is not uncommon to have to go through the procedure one or two more times as the synchronization of the throttle bodies is very, very dependent upon idle speed and every adjustment you make along the way affects the idle speed. If you do one step with the idle speed at 1000 rpm and two steps later you make an adjustment when the idle speed has varied by as little as 50 rpm, this method cannot be completed successfully. But the second time you go through the procedure, all your adjustments will be much smaller than the first time and the idle speed won’t be affected as much. This will make your subsequent adjustments more precise and throttle body nirvana will be achieved. While it is possible to sync all throttle bodies within .4” Hg at both 4200 rpm and 1000 rpm, it is ultimately up to you to decide what level of accuracy you want to achieve. In the end, however, I think you will find that this method is effective at reducing at least some of the vibration formerly experienced between 4000-4500 rpm. Keep in mind, though, that there are other things that could also cause that same vibration; this just deals with one of those causes.

 

[motorgod]

Skyway...

Great article, every thing explained in easy to understand language.

Thanks again

 

[3dogs]

Adjusting the TB air screws alone does not provide the most effective TB sync because they only compensate for air flow at idle. Most of your riding takes place at higher RPMs. The throttle valves (butter flys) of each throttle body need to be in sync with each other at high RPM.

You should not have to adjust the individual throttle stop screws to achieve this. This assumes that the throttle stop screws have not been grossly misadjusted at the factory (guy on the flow bench had one too many bottles of Sapporo the night before) or the lock nuts have come loose. Here is what I did to get my FJR in sync.

1) Get the engine hot by going for a short ride. When you are at 4200 RPM, squeeze you heals against the frame to feel the level of vibration. This highly precise measurement will be used later to determine how good a sync job you did.

2) Raise Tank and connect sync tool.

3) Turn all four TB air adjusting screws in until they are lightly seated.

4) Back each screw out 1, ½ turns (per service manual).

5) You may want to place a large fan in front of the radiator to keep things cool (including you).

6) Start engine.

7) The TBs should be out of sync to some extent but not more than 1 to 4 cm of Hg. The actual vacuum level does not matter.

8) REVING THE ENGINE Slowly rev the engine up to around 4000 RPM while watching your sync tool. What you are looking for is even vacuum levels as engine speed increases. If you try to do sync the TBs with the engine speed steady (say at 4000 RPM) you will find that the vacuum levels between TB will never be in sync no matter how many adjustments you make. It is more important for vacuum levels to be even during slow, smooth, engine acceleration and not at a steady throttle setting.

9) Using the butter fly sync screw between TBs #3 and #4 adjust the vac level so #3 and #4 are the same when you accelerate the engine as described in step 8, “REVING THE ENGINE above. This will take several tries. You may not get them exactly even either, but get them as close as you can (usually within 1 cm of Hg.).

10) Now perform the same procedure on TBs #1 and #2. You may have to rev the engine half a dozen times to get this close.

11) With vacuum levels for TB pairs #1/#2 and #3/#4 matched it’s time to sync the two pairs of TBs.

12) Rev the engine as described in step 8, REVING THE ENGINE while watching the two pairs of TBs. If they are off by more than 1 cm or Hg., an adjustment is needed.

13) The adjustment screw between the two pairs of TBs can only be accessed with the engine off. (The throttle has to be opened about ¾ of a turn to get a screw driver on the screw). Turn the screw about 1/8 (either way) of a turn and restart the engine.

14) Check the balance (vacuum level) between the two pairs of TBs. Shut the engine off and readjust as needed. (By now you and your FJR’s cooling system will appreciate the large fan you are using, step 5.)

15) When the two pairs of TBs are even (when you smoothly rev the engine) you are finished with this step.

16) Now let the engine idle. Adjust the idle speed to 1000. The tach on the FJR is very accurate. I checked it against a $500 electronic sync tool that counts the vacuum pulses during the intake stroke of cyl #1 and then generates an RPM signal.

17) Now it’s time (finally) to adjust the air screws on each TB. Use cyl #3 as reference and adjust the other cylinders to the same vacuum level as #3. The actual level does not matter (I know, everyone seems to be hung up on how may cm of HG., but it really doesn’t matter as long as idle speed is kept at 1000 RPM.)

18 Make a final idle adjustment (1000 RPM) and you done.

19) Go for a ride and check engine vibration at 4200 RPM, it should be better than when you started. It it’s worse, you screwed up the adjustment. The amount of improvement really depends on how far out of the sync the TBs were before you started.

 

[FJRocha]

WOW! :shock:

I never thought there was so much information about this subject :reading: Thank you guys for posting such great articles :fans:

 

[RadioHowie]

Dear moderator(s):

I don't even have my FJR (yet), but this thread deserves a sticky. Don't let it age off the server.

My $.02

 

[dobias]

OK, it's probably staring me in the eye but I can't find the idle adjustment knob!

It was there when I synched the throttle bodies last year. Since then I've had the lowers off several times but never needed to adjust the idle.

The manual pg.3-25 shows a very rudimentary sketch of it and I remember adjusting it while seated at a red light, but I can't find it now :dribble: .

I have the lowers off and want to locate the damned thing before I lose my sanity.

Please help, preferably with photos but a detailed location will do, too.

dobias :dribble:

 

[radman]

Right side, just below the line of the frame rail, at the top of the clutch cover. The right silver side cover points right at it.