Idle Sync Observations

[trailmug]

I read somewhere, and I can't find the exact quote, that some folks make a practice of doing the idle sync procedure at 4,000RPM instead of the specified idle speed. After taking things apart to do my valve clearance adjustment, I'd like to share a couple of observations:

1) The idle air adjustment screws adjust a bypass circuit around the throttle plates.. They do not adjust the throttle plates. If the adjustment to balance vacuum at 4,000RPM is notably different than at idle, the mix at idle could become very wrong for some cylinders.

2) The intake funnels in the air box are differing heights, which as I understand effectively tunes the intake of the inside (2 and 3) and outside (1 and 4) cylinders for peak torque at different engine speeds. Balancing vacuum at one particular above-idle engine speed may not produce the best results overall. Also, as I understand, differing inside and outside fuel trims are set from the factory.

 

[djstrong]

Here is the youtube video of a guy syncing at idle, but he does the final sync at 4000 RPM on an FZ6:
[ame=http://www.youtube.com/watch?v=UmLwyAPMBLI&feature=related]YouTube - How to synchronize your throttle bodies.[/ame]
I don't think he showed calibrating the tool which the instructions say needs to be done.

There are other threads on this forum that are of value to the sync issue, just search "sync".

Anyone have experience with trying syncing at idle or at 4000 RPM? Which is better?

 

[Fred]

That's the video that Hellgate and I made.

I learned the high RPM synch trick on old air cooled BMW engines. With only two large cylinders, any synchronization difference was very noticeable. Synching at high RPM improved things greatly.

You raise a couple of good points.

1. The synch screws do not adjust the throttle plates. These are adjusted by the screws between the throttle bodies. However, you should leave them alone. These are set on a flowbench at the factory, and unless they've been monkeyed with, you should assume that they are set correctly.

The synch screws are a trim. They provide the fine adjustment.

By synching at high RPM, you are sacrificing some smoothness at idle, because the air flow won't be spot on for all cylinders. Conversely, if you synch at idle, you will have imbalance at higher RPM. It's a tradeoff, and in my opinion, it's more important to be balanced at higher RPM's where you'll be while riding.

Also, going lean at idle isn't going to hurt anything. It's only at larger throttle openings that lean conditions become dangerous. Lean out an engine at idle, and it stalls. Lean it out at a high power setting and parts can melt.

2. I don't remember the airbox funnels being different lengths, but it's been a while since I've opened the airbox.

But if you follow the video, you'll see that we don't adjust cylinder #1. That's the cylinder that feeds the MAP sensor, which is what determines fueling. We set the other three cylinders to most closely mimic the behavior of cylinder #1. By doing this, we get the airflow as equal as possible.

Are you sure about the fuel trims being different? I haven't read anything about this one way or another. If you have a source, I'd love to read it.

I know that this was done on air cooled inline four cylinder engines, because the two inner cylinders ran hotter thanks to having less cooling fin area. I don't think that would be a major factor on a water cooled engine.

Yamaha may well have different fuel trim settings. The inner two injectors are on one channel, and the outer two are on the other. So it's definitely possible. But Yamaha still wants you to balance the vacuum levels across all four cylinders. So whatever fuel trim is set up, it is assuming that all four cylinders have equal vacuum, which translates to equal airflow.

That's my bike being tuned in the video, and it still runs like a champ. Synching the throttle bodies at high RPM took out some of the vibration at highway speeds, and nothing has broken, so I'm satisfied.

But as you point out, I am using a method different from the Yamaha method. It's up to each owner to decide if they want to follow this method or not. No harm will be done by using the method in the service manual.

Cheers,
Fred

 

[Red Wazp]

I have been taught and read where we should use #3 as your base to sync the others, eh?
In the past I've always sync'd my FJR at idle but I think next time I may try the 4K Sync

 

[buzzbomb]

That's the video that Hellgate and I made.

I learned the high RPM synch trick on old air cooled BMW engines. With only two large cylinders, any synchronization difference was very noticeable. Synching at high RPM improved things greatly.

You raise a couple of good points.

1. The synch screws do not adjust the throttle plates. These are adjusted by the screws between the throttle bodies. However, you should leave them alone. These are set on a flowbench at the factory, and unless they've been monkeyed with, you should assume that they are set correctly.

The synch screws are a trim. They provide the fine adjustment.

By synching at high RPM, you are sacrificing some smoothness at idle, because the air flow won't be spot on for all cylinders. Conversely, if you synch at idle, you will have imbalance at higher RPM. It's a tradeoff, and in my opinion, it's more important to be balanced at higher RPM's where you'll be while riding.

Also, going lean at idle isn't going to hurt anything. It's only at larger throttle openings that lean conditions become dangerous. Lean out an engine at idle, and it stalls. Lean it out at a high power setting and parts can melt.

2. I don't remember the airbox funnels being different lengths, but it's been a while since I've opened the airbox.

But if you follow the video, you'll see that we don't adjust cylinder #1. That's the cylinder that feeds the MAP sensor, which is what determines fueling. We set the other three cylinders to most closely mimic the behavior of cylinder #1. By doing this, we get the airflow as equal as possible.

Cheers,
Fred

Hi Fred, you're a bit wrong there about only cylinder #1 being linked to the MAP sensor. All four cylinders feed into the MAP sensor by small diameter rubber vacuum lines, so there's no risk of doing damage by altering cylinder #1 as much as any other cylinder.

And yes, the bike is fitted with different length intake funnels, the two centre ones are longer.

BB

 

[TownsendsFJR1300]

I believe the manual refers to cylinder #1 to base line off of.

I initially sync'ed mine at idle only and still had a pretty bad buzz at 4k, which got slightly better but still there...

I then sync'ed mine at idle and also/checking adjusting at 4k RPM (where I was getting a bit of buzziness) using air screws only.

You can have the manomoter dead on at idle, rev to 4k and see a cylinder pulling harder than another. I'd adjust to level them all out at both 4k and at idle, got rid of 90% of the buzz. Bike runs great!!!

 

[Fred]

Hi Fred, you're a bit wrong there about only cylinder #1 being linked to the MAP sensor. All four cylinders feed into the MAP sensor by small diameter rubber vacuum lines, so there's no risk of doing damage by altering cylinder #1 as much as any other cylinder.

Right you are. I had never traced the lines, just made an assumption based on Yamaha saying to set Cylinder 1 to a specific vacuum. I just looked at the manual and I see the lines that you're talking about.

Thanks for setting me straight on this.

Fred