Throttle body sync

[jestal]

When syncing the throttle bodies using the bypass air screws as normal the idle air flow is equalized but that doesn't address any possible imbalance at part throttle while cruising.

The more involved version of the throttle body syncing involves holding the engine at a higher operating RPM with the throttle (just like riding along) and adjusting the screws between the throttle bodies (on the linkage) to get the throttle blades synced off idle. Then you have to go back and re-sync the throttle bodies at idle using the bypass air screws.

Problem I was trying to work around was that just holding the motor at 4000 RPM or so and syncing the throttle linkage really doesn't sync them at the throttle openings seen at normal cruise conditions. It takes so little throttle opening to achieve 4000 in neutral that it doesn't represent cruise conditions.

One way to sync the throttle bodies at a higher throttle opening more representative of cruise conditions (where smoothness is most valued) is to put more load on the motor....How?? Unplug two of the injectors. The two dead cylinders will put a good bit of load on the engine so that you can open the throttle more. This load of the two dead cylinders puts enough load on the two remaining cylinders that they are running near the point that they would running down the road part throttle. Almost anyway based on how far open the throttle is at the grip. Closer than just free revving it.

Keep one hand on the throttle as you will have to start opening the throttle when you unplug injectors to keep it from stalling. If it stalls you'll have to give it some throttle to restart without stalling.

If you try this the first thing you will notice is that disconnecting the injectors doesn't really affect the engine vacuum in those ports. NOt even compared to the two running cylinders. Not too surprising since the engine is an air pump and it pumps the same amount of air (and creates the same vacuum level when throttled) whether the cylinder is running or not.

In any case, disconnect the two outboard cylinders first and then sync the two inboard cylinders, 3 and 4, at 4000 RPM. Since the linkage screws only adjust the two adjacent cylinders anyway this is fine since you are syncing two running cylinders. Now disconnect 1 and 2 and sync 4 to 3. Now disconnect 3 and 4 and sync 1 to 2. Go thru this several times and it is possible to get the 4 cylinders very close well off idle.

Go back and redo the idle sync with the air bypass screws and you are good at idle.

I find that I have to turn the idle speed well down with the manual knob so as to keep some adjustment range with the knob after the sync at idle is done.

This works well for me. If anyone tries it let me know how it works for you.

 

[twowheelnut]

Even makes sense to me! However, it'll have to wait as the bike goes in next week for the valve adjustment. Gulp! Me and the tech have reviewed all the stuff to be done and the TBS is on the list for them to do. I hold little hope of convincing them to try your procedure, though. So next time for sure. Thanks!

 

[radman]

I'd always felt that the 4 thou synch worked, but not as well as it would if the motor was loaded. Dyno time is too spendy to use to synch TB's. And I dropped the screwdriver twice while on the freeway, and the wife got tired of holding the tank and me at the same time. Good idea!

 

[v65]

Any chance of this getting put somewhere permanent?

 

[norcal]

What were the riding results, was there less engine vibration at hiway speeds?

Vibration is not an issue on my 05.

Did you use mercury tube for the job?

 

[radman]

What were the riding results, was there less engine vibration at hiway speeds?Vibration is not an issue on my 05.

Did you use mercury tube for the job?

Nope. This is jestals custom balance equalization transmogrifier device..........

 

[jestal]

I used mercury tubes. What used to be called CarbStix back when I bought them decades ago.

Vibration really isn't much of an issue to me either. I didn't ride it immediately before and after the alternative sync method so comparing vibration is pretty hard. I did the alternate sync method when prepping it this spring after a winter of dissassembly and various farkling.

 

[markjenn]

The theory seems sound. I do wonder what the non-firing cylinders are doing to the O2 sensor readings - might the computer start doing something odd with the firing cylinders that would affect the balance. Probably not, but you never know.

Speaking personally, my engine seems quite smooth at all throttle settings just using the std syncing with the bleed screws, so I'm taking the "if it ain't broke, don't fix it" approach. But if your engine is smooth at idle and rough at load, this might be something interesting to try.

- Mark

 

[ionbeam]

I do wonder what the non-firing cylinders are doing to the O2 sensor readings

On '03-'05 models the O2 is not in play when doing a sync. In fact, on these model years the O2 is in use in only a very narrow set of conditions. Dunno about the '06 but doubt that the O2 would be in operation in sync conditions. If in doubt, unplug the sucker.

 

[jestal]

I don't think the O2 sensor input is going to affect much regarding the sync when injectors are disconnected and/or the engine RPM is elevated off idle. The vacuum levels read in the ports via the mercury tubes are caused by the pumping of the engine and the throttle restriction. Little or nothing to do with the air/fuel ratio as determined by the O2 sensor and the closed loop fuel correction routine. You can watch the vacuum levels before and after disconnecting the injector and it changes very very little even between the cylinder running and dead so a slight change in the air/fuel ratio isn't likely to affect the sync.

I wasn't trying to fix anything, per se. Just curious as to how close the throttle linkage was syncronized vs. just the idle sync. For idle quality and just off idle the idle sync is obviously pretty important. For running down the road the throttle linkage determines the majority of the sync as the air flow is way beyond what the idle bypass circuits (idle air screws) will provide.

 

[Toecutter]

I wasn't trying to fix anything, per se. Just curious as to how close the throttle linkage was syncronized vs. just the idle sync.

So, how close was it? If it was out by much, did you notice a difference in performance afterward?

 

[jestal]

Mine was reasonably close even off idle with the added load of dead cylinders. It was within a line and a half on the CarbStix at 4000 when disabling cylinders to get more throttle opening. I brought it all in line perfectly.

The idle sync was perfect as I had done that previously but it changed slightly with the adjustments to the linkage to get the 4000 RPM point good. Easy to bring back in line with the air bypass screws.

No change in idle since the sync was good at idle anyway. At cruise, it is hard to say. Remembering from last seasons riding it really doesn't seem any smoother but I didn't have much complaints about that anyway and it wasn't that far off at 4000. At least mentally I know it is right....LOL. THAT makes me feel better.

 

[kindofblue]

When syncing the throttle bodies using the bypass air screws as normal the idle air flow is equalized but that doesn't address any possible imbalance at part throttle while cruising.
The more involved version of the throttle body syncing involves holding the engine at a higher operating RPM with the throttle (just like riding along) and adjusting the screws between the throttle bodies (on the linkage) to get the throttle blades synced off idle. Then you have to go back and re-sync the throttle bodies at idle using the bypass air screws.

Problem I was trying to work around was that just holding the motor at 4000 RPM or so and syncing the throttle linkage really doesn't sync them at the throttle openings seen at normal cruise conditions. It takes so little throttle opening to achieve 4000 in neutral that it doesn't represent cruise conditions.

One way to sync the throttle bodies at a higher throttle opening more representative of cruise conditions (where smoothness is most valued) is to put more load on the motor....How?? Unplug two of the injectors. The two dead cylinders will put a good bit of load on the engine so that you can open the throttle more. This load of the two dead cylinders puts enough load on the two remaining cylinders that they are running near the point that they would running down the road part throttle. Almost anyway based on how far open the throttle is at the grip. Closer than just free revving it.

Keep one hand on the throttle as you will have to start opening the throttle when you unplug injectors to keep it from stalling. If it stalls you'll have to give it some throttle to restart without stalling.

If you try this the first thing you will notice is that disconnecting the injectors doesn't really affect the engine vacuum in those ports. NOt even compared to the two running cylinders. Not too surprising since the engine is an air pump and it pumps the same amount of air (and creates the same vacuum level when throttled) whether the cylinder is running or not.

In any case, disconnect the two outboard cylinders first and then sync the two inboard cylinders, 3 and 4, at 4000 RPM. Since the linkage screws only adjust the two adjacent cylinders anyway this is fine since you are syncing two running cylinders. Now disconnect 1 and 2 and sync 4 to 3. Now disconnect 3 and 4 and sync 1 to 2. Go thru this several times and it is possible to get the 4 cylinders very close well off idle.

Go back and redo the idle sync with the air bypass screws and you are good at idle.

I find that I have to turn the idle speed well down with the manual knob so as to keep some adjustment range with the knob after the sync at idle is done.

This works well for me. If anyone tries it let me know how it works for you.

Al, I've been trying to visualize what you did here (e.g., adjusting the screws between the throttle bodies (on the linkage) and unplugging the injectors), to no avail. Any chance you might be willing to take some pictures and maybe put it together with the text next time you do it? Thanks.

 

[Toecutter]

Any chance you might be willing to take some pictures and maybe put it together with the text next time you do it?

Jestal doesn't do many pics, but he'll explain the hell outta stuff. :blink:

 

[Toecutter]

Any chance of this getting put somewhere permanent?

What I do is copy the thread URL, email it to myself (yahoo), then put it into a folder I call "FJR Forum threads". That way it's pretty permanent, for me anyway, and who else matters? :bleh:

 

[RTSR1/FJR]

When syncing the throttle bodies using the bypass air screws as normal the idle air flow is equalized but that doesn't address any possible imbalance at part throttle while cruising.
The more involved version of the throttle body syncing involves holding the engine at a higher operating RPM with the throttle (just like riding along) and adjusting the screws between the throttle bodies (on the linkage) to get the throttle blades synced off idle. Then you have to go back and re-sync the throttle bodies at idle using the bypass air screws.

Problem I was trying to work around was that just holding the motor at 4000 RPM or so and syncing the throttle linkage really doesn't sync them at the throttle openings seen at normal cruise conditions. It takes so little throttle opening to achieve 4000 in neutral that it doesn't represent cruise conditions.

One way to sync the throttle bodies at a higher throttle opening more representative of cruise conditions (where smoothness is most valued) is to put more load on the motor....How?? Unplug two of the injectors. The two dead cylinders will put a good bit of load on the engine so that you can open the throttle more. This load of the two dead cylinders puts enough load on the two remaining cylinders that they are running near the point that they would running down the road part throttle. Almost anyway based on how far open the throttle is at the grip. Closer than just free revving it.

Keep one hand on the throttle as you will have to start opening the throttle when you unplug injectors to keep it from stalling. If it stalls you'll have to give it some throttle to restart without stalling.

If you try this the first thing you will notice is that disconnecting the injectors doesn't really affect the engine vacuum in those ports. NOt even compared to the two running cylinders. Not too surprising since the engine is an air pump and it pumps the same amount of air (and creates the same vacuum level when throttled) whether the cylinder is running or not.

In any case, disconnect the two outboard cylinders first and then sync the two inboard cylinders, 3 and 4, at 4000 RPM. Since the linkage screws only adjust the two adjacent cylinders anyway this is fine since you are syncing two running cylinders. Now disconnect 1 and 2 and sync 4 to 3. Now disconnect 3 and 4 and sync 1 to 2. Go thru this several times and it is possible to get the 4 cylinders very close well off idle.

Go back and redo the idle sync with the air bypass screws and you are good at idle.

I find that I have to turn the idle speed well down with the manual knob so as to keep some adjustment range with the knob after the sync at idle is done.

This works well for me. If anyone tries it let me know how it works for you.

I'm just wondering here if maybe the air bleeds shouldn't be fully closed to get a more accurate sync at 4000 rpm off of the throttle plates and then set the sync at idle with the air bleeds. Any thoughts on this?

 

[jestal]

I'm just wondering here if maybe the air bleeds shouldn't be fully closed to get a more accurate sync at 4000 rpm off of the throttle plates and then set the sync at idle with the air bleeds. Any thoughts on this?

You could do it either way I would say.... Since the idle air bleeds have little effect at 4000 it is not going to matter that much. Sooner or later you have to open the idle air bleeds up a specific amount (1/4 turn) to start the sync at true idle so opening each of them a specific/equal amount for starters is what is important. No real way to do that other than look at the number of turns or fractions there-of. I tended toward setting the off idle sync with the air bleeds open a set amount to include their contribution to airflow at part throttle (albeit a very small amount of flow) but there is certainly merit to doing it with the air bleeds completely closed. At the end of the day I doubt that it will matter due to the small flow at thru the bleeds at part throttle. The main thing is to get the sync correct at part throttle by adjusting the throttle linkage screws and putting some sort of dummy load on the engine (by disconnecting injectors to kill cylinders not being synced) so the throttle opening is representative of where you are riding at part throttle....THEN go back and set the idle sync ( the "normal" TBS procedure) using the air screws as they were designed.

 

[sprint_st]

I'm just wondering here if maybe the air bleeds shouldn't be fully closed to get a more accurate sync at 4000 rpm off of the throttle plates and then set the sync at idle with the air bleeds. Any thoughts on this?

You could do it either way I would say.... Since the idle air bleeds have little effect at 4000 it is not going to matter that much. Sooner or later you have to open the idle air bleeds up a specific amount (1/4 turn) to start the sync at true idle so opening each of them a specific/equal amount for starters is what is important. No real way to do that other than look at the number of turns or fractions there-of. I tended toward setting the off idle sync with the air bleeds open a set amount to include their contribution to airflow at part throttle (albeit a very small amount of flow) but there is certainly merit to doing it with the air bleeds completely closed. At the end of the day I doubt that it will matter due to the small flow at thru the bleeds at part throttle. The main thing is to get the sync correct at part throttle by adjusting the throttle linkage screws and putting some sort of dummy load on the engine (by disconnecting injectors to kill cylinders not being synced) so the throttle opening is representative of where you are riding at part throttle....THEN go back and set the idle sync ( the "normal" TBS procedure) using the air screws as they were designed.

More of an observation or comment than any type of recomendation. I've been syncing carbs for a long time and FI for about three years (actually I didn't sync them because they were ok). When I first started I did it because the manual said to. Later I only changed things if my idle was off and/or I could visually see the butterflies weren't braking at the same time. My bikes have always run well, and I noticed that when I started adjusting I usually had to play with them quite a long time to get them where I liked them to be.

 

[djsmith1000]

Hello,

Sorry to resurrect an old thread, but I figured its OK since it was posted in the FAQs

I tried this method with my new homemade 4 way differential manometer this afternoon. I would NOT recommend it. I found that disconnecting the injectors has a profound effect on the vacuum. I like the idea of generating load, but this is not the way to do it.

My theory on why is as follows.

When the intake valve opens, there is some residual pressure left in the cylinder. This varies based on combustion, exhaust pressure waves (functions of pressure, temperature, density, composition,.... )etc. The cylinder pressure at IVO may have a large effect on the amount of air that is drawn into the cylinder. This seems to be a plausible explanation to the difference in intake pressure.

Hope this helps. I tried the other method of bringing the engine slowly up to speed, and was not satisfied with it either. Found that the outer two cylinders tended to build up lots of vacuum under certain conditions. So.... I did the best I could, set and synced the idle, and threw it back together.

Results... it helped significantly. Actually, one of the first things I noticed is that my AE tended to shift smoother and faster.