Throttle body sync questions - Kawasaki Versys Forum
 
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Old 06-21-2014, 11:45 PM Thread Starter
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Throttle body sync questions

So I did a TBS (throttle body sync) and had a few issues come up. First, both screws were turned all the way to the right on a new, last year, 2012. The bike has just over 2000 miles. When I turned the left screw (per the manual) to adjust the levels they became more unbalanced. I had to adjust the right screw to get them balanced. I am using a home built manometer using clear tubing filled with 2 cycle oil. The tubes are tight on the nipples and all seems ok. I am using the dash tach varying the rpms around the 1300 goal to see if there is much fluxuation of the level in the tubes. There is very little. I have the air box unplugged. Is it important to have the plug in, the hose connected, and the filter taped to the throttle bodies? The bike seems to run ok after the sync but I want to be sure that it is set correctly. I do know that the fluid level is even at idle but goes out of balance if I raise the rpms. This brings me to my next set of questions.

I've seen the suggestion come up about syncing at higher rpms to smooth out the vibs around the 4000-5000 area. Does this really work? I have also read that the sync is only for stability at idle and up to a low rpm. A Google search came up with a post on a FJR forum about adjusting the throttle plate screws first at the desired high rpm then the air screws at idle. Yep, I know that an FJR has two more cylinders but do we have the option to do this on our twins?

Last edited by david3921; 06-21-2014 at 11:49 PM.
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Old 06-22-2014, 04:34 AM
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Idle speed is the only speed where the throttle body vacuum synchronization is required for efficient engine starting, good idle quality and driveability.

Once the butterfly valves begin to open, the area of the opening that permits additional airflow rises quickly. It’s only at the very slight throttle opening at idle speed that minute changes in the bypass adjustment screw opening are apparent. Remember, the throttle is almost closed. Very small changes in throttle opening affect idle speed and smoothness. Once the throttle begins to open farther, these small changes are insignificant and irrelevant.

Throttle valves are joined together by a fixed shaft, and their synchronization is actually not adjustable. The phrase “synching the carbs” is used as if it were a performance issue. It comes from an era when each carb or TB in a multiple rack were operated by separate cables or linkages, rather than a common shaft (or, in the case of CV carbs, by vacuum alone)... In those cases, you really did have to synch the throttles to ensure that they were even at part-opening and that all reached wide open position at the same point.

When you adjust your TB vacuum sync at 1,300 rpm, you'll notice that it goes off synch when you open the throttles as rpm rises, and then goes back to being balanced at higher rpm. The difference you're seeing on your manometer is only at very slight throttle opening and under no engine load... Opening throttles too fast may cause the liquid in your manometer to be sucked in the throttle with a higher vacuum level.
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Old 06-22-2014, 11:04 AM Thread Starter
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Thanks for the reply Invader. I almost called out to you in the topic as you are our resident guru on this and most subjects related to the V. I have a 1984 V65 Magna that I have done the carb sync on so I am familiar with the process there. I was just a little concerned that I had to adjust the right side rather than the left. Is there any benefit to setting both sides to the actual vacuum reading listed in the manual? I do have actual vacuum gauges I can hook up and dial them both in that way. From my reading, the conscience is balance is more important than accuracy.
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Old 06-22-2014, 11:41 AM
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Quote:
Originally Posted by invader View Post
Idle speed is the only speed where the throttle body vacuum synchronization is required for efficient engine starting, good idle quality and driveability.

Once the butterfly valves begin to open, the area of the opening that permits additional airflow rises quickly. It’s only at the very slight throttle opening at idle speed that minute changes in the bypass adjustment screw opening are apparent. Remember, the throttle is almost closed. Very small changes in throttle opening affect idle speed and smoothness. Once the throttle begins to open farther, these small changes are insignificant and irrelevant.

Throttle valves are joined together by a fixed shaft, and their synchronization is actually not adjustable. The phrase “synching the carbs” is used as if it were a performance issue. It comes from an era when each carb or TB in a multiple rack were operated by separate cables or linkages, rather than a common shaft (or, in the case of CV carbs, by vacuum alone)... In those cases, you really did have to synch the throttles to ensure that they were even at part-opening and that all reached wide open position at the same point.

When you adjust your TB vacuum sync at 1,300 rpm, you'll notice that it goes off synch when you open the throttles as rpm rises, and then goes back to being balanced at higher rpm. The difference you're seeing on your manometer is only at very slight throttle opening and under no engine load... Opening throttles too fast may cause the liquid in your manometer to be sucked in the throttle with a higher vacuum level.
It's great this forum has you as a member. Great info!
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Old 06-22-2014, 04:06 PM
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Most seem to need to have the left TB's adjustment screw open, but not all. Yours had both closed, and now with the right side open. Whatever it takes to have them balanced at 1,300 rpm is just fine.
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Old 06-22-2014, 04:43 PM
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Seems to me that I TOO adjusted the right screw, but that was last year....

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Old 06-23-2014, 12:30 AM
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If the Right screw was set correctly at the factory or when the dealer put the bike together, then it should not need to be moved. It sounds like it was never set correctly or someone else tried and failed to sync them before.

The Service Manual says you need:
Engine Vacuum
Standard: 37.9 ±1.3 kPa (285 ±10 mmHg) at Idle Speed 1300 ±50 r/min (rpm)

Think of the Screws as bleed screws, they each will let in a bit of air - hence creating a vacuum. You want each throttle body sucking in the same amount.
If you have a sync tool that used a vacuum guage for each cylinder then you set them both to be the same at factory settings.

With the Balancing/Difference tool like a DIY home made Oil in Tube design, you cannot see what the vacuum measurement is, only that one TB is more than the other - hence why you only move the left screw - you change one TB to sync to the other.

If the right one was screwed all the way to the right - then it was closed and no vacuum... you would never sync them!
Open Right side up counting the number of turns then set it to about 25% open. Then try syncing the TB's (It will not be the correct vacuum value - but you will be now able to sync them)
Check RPM's - adjust if needed... check Sync adjust again, check RPMs again adjust etc
Every so often blip/open throttle to about 3500-4000 rpm for 1-2 sec then release throttle and watch the Sync it should settle and RPM's should still be 1300ish.

Once you RPMs and TB Sync are stable you are done.

how this helps someone.
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Old 06-23-2014, 01:28 AM
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Closing the TB's throttle valve bypass circuit adjustment screw raises its vacuum level. Some came balanced with the left screw open and right screw closed, others are vice versa. Whichever right or left TB closed screw is left closed, and the other TB's open screw is fine tuned to have vacuum levels equal in both TB's... If they happen to be both closed, the adjustment screw on the TB with higher vacuum level is opened to balance both TB's at a 1,300 rpm idle speed, while the other TB screw is left closed.
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