Yamaha FZ-09 Forum banner

21 - 40 of 51 Posts

·
Registered
Joined
·
83 Posts
When you close the throttle at any speed the air bypass is in effect, which is why you can get hesitation when you crack the throttle open and the TB's are out of sync. This can happen at any rpm.
And, the first time I did a TB sync, the engine was noticeably smoother because the TB's were a fair way out.
I'll rely on empirical evidence on this one.
Yes that makes perfect sense, because your are closing the throttle which brings the sync in to play. What I was trying to get at was the sync only has an effect at the closed or slightly open throttle position. This didn't sound like the condition the OP was talking about, but I could be wrong.

As far as it making a difference at any other throttle position, I will to agree to disagree.
 

·
Registered
Joined
·
5,286 Posts
An N/A intake system operates at a vacuum, even upstream of the TB's. Vacuums suck, anything, through any hole.
So a bleed valve will always let air through unless it is physically blocked.
 

·
Registered
Joined
·
83 Posts
Still wrong, the piston moving down on the intake stroke causes a low pressure area, the higher atmospheric pressure pushes the air into the engine.
 

·
Registered
Joined
·
137 Posts
And completely ignoring the laws of physics.
Your photo is helpful, and we can all agree that the size of the bypass ports are insignificant compared to open throttle plates. Just not sure if the "laws of physics" render their settings 100.0% inconsequential at open throttle, that's all. If they impact airflow by even 0.5% then logically that could impact performance as many of us believe is happening.

Once again, third-party links would be helpful here.
 

·
Registered
Joined
·
5,286 Posts
Still wrong, the piston moving down on the intake stroke causes a low pressure area, the higher atmospheric pressure pushes the air into the engine.
And what do you call the low pressure area? A vacuum? A simile for vacuous.
 

·
Registered
Joined
·
83 Posts
a vacuum by definition, is area that is devoid of all matter. Yes it is commonly used incorrectly to describe a low pressure area.

I am not pulling this out of my a** just for shits sake. During our 4th year MC mechanic school program, this exact question came up when we where covering TB syncs. There are other factors at play such as the Venturi effect when air passes over tube along with air will follow the path of least resistance. The instructor explained this in great detail, which I am not going to regurgitate. He later proved this on the dyno.

Believe what you want.

Peace out
 

·
Registered
Joined
·
90 Posts
An engine is basically an air pump. You‘ll notice Merriam Webster gives specific definitions for a vacuum related to this, actually 2 can be used. So it’s unfair to say it’s used incorrectly in this context.
 

·
Registered
Joined
·
83 Posts
Yes your right, another definition was added due to the fact that over the years ppl where using the term to describe a low pressure area, which is fine as long as you understand its the difference in pressures that create air flow. When you hear the work "suck" to describe vacuum that's when the word is being used incorrectly.

Yes a engine is basically an air pump and so is a vacuum cleaner, air compressor ect, none of which magically "suck" air.

When EFI starting becoming mainstream in the late 80's I was working as a mechanic in the automotive world. I took some journeyman updating courses on EFI, the question was asked why did engineers call it a Manifold Absolute Pressure sensor (MAP) when its just a vacuum sensor. The engineers where trying to change the way mechanics were incorrectly assuming that air was being sucked into the engine when in reality it was being pushed into the engine by atmospheric pressure. When you add a turbocharger or supercharger to the equation, this becomes even more relevant.

The first step in diagnosing anything is knowing how it truly works. Repair by attrition usually follows when you don't have a clear grasp of how it works.
 

·
Registered
Joined
·
137 Posts
If I get your point, 9Lives, you're saying that when two passages of different size are exposed to the same pressure differential the smaller passage will admit no air whatsoever.

The problem I'm having with this logic is that I can partially block one nostril and it still flows air when I breathe in & out. It doesn't stop just becaue there's a path of less resistance right next to it. Both nostrils continue to flow air, and the degree to which I "adjust" the one nostril affects the airflow reaching my lungs whether I'm relaxing or sprinting at top speed.
 

·
Registered
Joined
·
26 Posts
Hey all,
So I have been having engine stutter issues on my 2016 FZ09. It usually comes on pretty aggressive when I slow roll the throttle and try to maintain speed. The bike tends to jerk forward a bit and then sounds like the engine cuts out and kicks back in. Very odd. Anyways, I’ve replaced the spark plugs to attempt to fix. No avail. I took it to Freedom Powersports and asked them to do a throttle body sync on it as I don’t think this bike has ever had one done. (9k miles currently). The guy told me Yamaha says to NOT do a sync on the throttle body. And they are not allowed to do those on FZ. Not sure how true this is, people Ive heard from say their bike has never ran smoother and better after syncing it up. Has anyone ever heard of this before? Yamaha not allowing TB syncs.
check the fuel line under the tank and spark plugs
 

·
Registered
Joined
·
17 Posts
So you have never heard of someone not willing to do a sync on an FZ09? I thought it was weird he said Yamaha doesn’t want people doing it. I even asked, well how are you supposed to fix the cylinders when they get out of sync? And he said they don’t get out of sync. I laughed and told him to replace my O2 sensor and TPS lol
Why not just ask them to troubleshoot the problem for you? Instead of throwing ideas and parts at it? Could be a fueling or spark delivery problem.
 

·
Registered
Joined
·
3 Posts
I also have that problem on my 2019 MT09

if I’m at a higher RPM example 3rd gear 10,000 RPM downshift two 2nd Gear if I roll off quickly the bike shuts off,

I can duplicate the same problem with the clutch rolled in hi RPM fast roll off with the clutch depressed and the bike shorts off even without downshifting, if I roll off slowly the bike will stay on please any solutions would help I also don’t know what to do wood flashing the ECu Solve this problem
 

·
Registered
Joined
·
299 Posts
To OP.
Was your TPS changed out?
If so and you are still having this issue I would change your APS, assuming you already had/have your ECU flashed which helps smooth everything out.
I had the issue you described for a long time. I tried spark plugs, coil packs, tb sync, diff fuels, new throttle tube, and kevs O2 controller all to no avail. Almost gave up. After seeing some posts on here changed my TPS and APS and problem finally solved!

I believe the cause is one or both (APS & TPS) give out an unstable, call it twitchy, signal which in turn causes your tb butterfly valves to "twitch". The joys of ride by wire 😉
 

·
Registered
Joined
·
113 Posts
That’s what I thought. Not sure what freedom Powersports is talking about when they said they aren’t allowed to perform, per Yamaha.
That's Freedom Powersports in Canton?? I cant believe they said they were told not to do it lol. Did you show them the maintenance schedule from your operation manual? Maybe call Mountain Motorsports in Marietta or Roswell whichever is closer for you.

On another note I live over in Adairsville if you ever want to hit the road for a ride shoot me a PM.
 

·
Registered
Joined
·
137 Posts
Yes your right and I am wrong, pls let this tread die a quick death.
Your technical explanations were interesting to a number of us in this forum; just hard to reconcile with personal experience. No offense intended.
 
21 - 40 of 51 Posts
Top