Throttle body sync

[Charlie Hoss]

I found, thru some experimentation, that any unwanted vibes at different RPMs are mechanical in nature, rather than FI related.

My 05 is generally smooth but I get some vibes around 70 to 75 and 85 to 90 MPH. I reached these speeds and more, then hit the kill switch, or, just closed the throttle, with no difference in vibe levels until the motor was out of the RPM range.

I do the TBS to ensure a smooth idle, and the 4K TBS may have similar benefits, but I doubt that reduced vibration is one of them.

 

[jestal]

I thought this old thread had rusted away.....

Sync how you want but adding load to the engine is the only way to get an accurate sync at higher RPMs that represents where the engine is operating under load going down the road. Since this approach is recommended for syncing at 4000 RPM it will have absolutely no effect on the "normal" idle sync procedure as done with the idle air bypass screws.

Disconnecting injectors will have a minimal effect on the intake vacuum in the cylinders being disconnected based on my observations but that is of absolutely no concern whatsoever. The cylinders are being disconnected to create load and are NOT being synced and are NOT being synced to the other two cylinders. Even if the vacuum in the dead cylinders doubled or halved....WHO CARES...??? The cylinders being matched or synced are the other two that are still running correctly. The effect of the disconnected two cylinders, other than creating load to allow a larger (more representative) throttle opening in the ones being synced, is of little concern.

Disconnect the injectors to the outer cylinders, 1 and 4, and sync 2 and 3 at 4000 with the throttle shaft adjusters. Reconnect injectors. Disconnect injectors 3 and 4 and sync 1 to 2. Reconnect injectors. Disconnect injectors 1 and 2. Sync 4 to 3. Forget what the vacuum is in the disconnected cylinders. It is not being used.

One thing that will happen that is maybe the source of the confusion is that the vacuum in the two cylinders that are still running will definitely drop....i.e...if the engine is held at 4000 and the vacuum in all cylinders is 16 inches and 1 and 4 injectors are then disconnected it is likely that the vacuum in 2 and 3 will drop to 10 inches if the engine is held at 4000. That is because the dead cylinders are putting more load on the running cylinders (2 and 3) and the throttle will have to be opened further to maintain 4000 RPM on only two cylinders. That is the whole goal of this exercise. To sync the throttle blades at 4000 at a vacuum point more representative of where the egine is operating at under load on the highway. Syncing it at an overrun vacuum level (by simply revving the engine) is somewhat pointless. So, if anyone is worried about the vacuum changing in the running cylinders when the other two injectors are disconnected they shouldn't be. That is the whole reason for disconnecting the injectors...to create load on the running cylinders and lower the vacuum level to where the engine operates at for a more representative sync.

Debate what the vacuum does or how it happens forever but it is still a very usefull means of creating load on the engine to work on the remaining running cylinders. As long as you are matching or syncing cylinders to each other that are not disconnected (injectors) the vacuum in the disconnected (injector) cylinders is a moot point.

How a throttle body sync at IDLE and no load can affect shifting speed and smoothness going down the road is unbelieveable to me. Ever consider the placebo affect??

The main point of this alternate procedure is to provide a means of syncing the throttle blades with the throttle shaft adjusters to effect a meaninful sync of the throttle bodies at an RPM/load representative of that the engine operates at. The simple idle sync with the idle air bypass screws is only for idle smoothness and has little to no effect once the throttle blades are cracked open or the engine is under load.

If you do sync at higher speeds with the throttle shaft linkage adjusters you will definitely have to go back and repeat the idle sync with the idle air bypass screws as changing the throttle shaft orientation/sync is going to throw off the idle sync. That is why the screws are there to adjust only at idle.

 

[djsmith1000]

Yes, I thought about the placebo effect, but engine runs significantly better with the sync. I am pretty picky though. Since the EFI system probably has vacuum compensation, this MIGHT have something to do with it, although not likely since the ports are tied together for the MAP sensor. Not really sure why the shifting is improved. I actually wasnt expecting it, but noticed it immediately.

And I do understand what vacuum conditions to expect for the new load.

As far as creating load with dead cylinders, your logic seems correct, but actually looking at the tubes says different. Maybe if I get ambitious I'll try it again soon. However, whenever you unplug injectors, you are really messing with the gas dynamics in your engine. Even you exhaust is affected because you flow resistance and wave propagation rates changes due to the temperature of the gas. Not saying I can one up you on engine knowledge by any means cuz I've read enough of your posts, but my experimenting and intuition indicate that your explanation is a bit of an oversimplification. However, it may be the best method available and it may work great. Youve probably got alot more experience with your method, and maybe with a little more patience I could have gotten better results.

 

[PA1195]

Hello, Jestal's method has merit...and if I end up not selling my ride I'll think about experimenting with that...in the past for my '06 and '07 FJR, I just put the bike on the stand, ran it to 3500 rpm in gear, and put on the rear brake enough to load the engine, adjusted the rpm's back up to 3500, and quickly noted the MP values...this rude technique does allow some additional load (don't know how much), and the rear brake seems to take it in stride if allowed to cool with a fan running on it during the test...then I reset them as required and reran the test to fine tune the cyl pairs and finally 1/2 vs 3/4...Jestal, how much MP do you see on the cyls of interest with your technique at the rpm's you run the test at with the other two cyls fuel dead?

Gary in Fairbanks w/Geese and Cranes flying about so Fall is coming.

 

[jestal]

As far as creating load with dead cylinders, your logic seems correct, but actually looking at the tubes says different.

Not to belabor it , but, how does the vacuum reading(s) contradict this approach for putting a little load on the engine?? When the engine is idling and injectors are disconnected I see little change in the disabled cylinders for vacuum readings but the RPM drops. Raise the RPM to get back to the original RPM and the vacuum is now lower than it was before in both the operating and dead cylinders. This is what I observe and expect to happen. Keeping the RPM constant while disabling cylinders will put more load on the other cylinders and will result in lower vacuum levels. Not because of any "gas dynamics" in the engine but because there is more load on the remaining cylinders. The fact that the vacuum level drops with the dead cylinders (at constant RPM) proves that the dead cylinders are putting more load on the engine hence the observations from the carb stix tends to validate the idea proposed, not stand in contradiciton to it.

Certainly there is a theoretical effect on vacuum from the cylinder not firing but for all practical purposes it can be ignored. Besides, as stated, you are syncing the cylinders that are still firing among themselves so the conditions in the dead cylinders are of no real concern as long as they are putting load on the engine.

There is a little cross talk with the MAP signal plumbing but it has little affect on the actual vacuum levels. Try idling and watch your readings and pinch off vacuum lines to the MAP sensor and watch the readings and see for yourself. There is "vacuum compensation" per se....since the fuel injection system is a speed density system it uses manifold absolute pressure as the basis for calculating fueling. Baro - MAP = vacuum. As far as the speed density calculation in the fueling algorithm vacuum or MAP could be used interchangably so the system is inherently MAP/vacuum compensating. There is no single cylinder compensation which is why syncing the throttle bodies is a good idea. The MAP reading is an average of the cylinders and if one strays from the average the fueling will be off as a result. Hence the sync.

Gary, I have no recollection of the actual vacuum levels I saw at the time. Seems like it was about 1.5 major divisions on the carb stix which is roughly 1.5 inches I think. I really don't worry about the actual vacuum level as it is unimportant for the purposes of the sync. Balancing the vacuum levels is the only real concern to me at the moment so I just don't even remember trying to remember the actual measured value.

I think Yamaha calls out a vacuum level to shoot for so that techs/people get in the ballpark for the correct sync on the first try. With some experimentation it is obvious where to set the idle speed and the initial settings on the bypass air screws for starters. If you miss on the initial idle speed and initial bypass air screws settings the sync will still work OK but you might not be able to set the idle low (or high) enough with the idle speed control stop. You would have to reset the idle stop and then redo the sync, compensating with the initial setting of the idle bypass screws. By specing a vacuum to start with the service manual procedure just gets you in the ballpark quicker....maybe.

 

[nick]

Cracking good technical thread guys ! - My logic seems to agree with disconnecting two injectors to put "load" on the engine, so I will be trying this method very soon..

Nick

 

[bramfrank]

Old threads never die, they just sit there, waiting for someone to point to them as reference, which stirs them back to life like zombies.

It is all very well that we want the throttle bodies properly synchronised at speed - moreso than at Idle, perhaps - but what counts is the relative positions of the thrrottle bodies at the point they will e with the engine running under load and that has nothing to do with the speed of the engine, per-se, but with the LOAD on the engine to make that RPM.

So I believe that the ONLY way to properly do properly sync the system at 4K RPMs would be on a dyno, which can provide a proper load to the drive train, allowing the mechanic to adjust the throttle bodies and flies when they are where they would be when the machine is running at cruising speed in real life. (I suppose one might even be able to somehow achieve this through trial and error while rolling down the road).

Disconnecting a couple of cylinders likely won't provide drag similar to what the real world does. It is probably better than nothing, mind you. But I don't think it will quite do the job.

Having said that, I have ZERO bar vibes at speed and only very slight vibes in my pegs at 3800 - and the last TBS I did required that I adjust only one cylinder - and that only a touch-up. I suppose it's like valve adjusts - the vast majority are perfect at 24K, but you have to check.

 

[just roy]

if you don't think disconnecting 2 cylinders will provide much load think about an air compressor or kicking over a high compression 500cc motor at 4000 rpm.