2018zf800trail.
The previous weekend I did a 100+ mile trip and the machine ran great.   I went to load it on the trailer this past Saturday and it was really loud.  Like it had straight pipes.  I did see a lot of dust blowing over the rear driver side tire. After about a minute or so it was quiet again.  So I loaded and went riding.  Same thing happened and while it was loud I did get one backfire upon acceleration.   After a minute or so it was quiet and ran great for the day.  Got home and same thing.  I took off one heat shield and all my springs are there.  No visible exhaust leak.  Couldn't tell if the valves were noisy or not. 
Any ideas?

[2015 Z Force 800 53/Trail EPS]

2018zf800trail.
The previous weekend I did a 100+ mile trip and the machine ran great.   I went to load it on the trailer this past Saturday and it was really loud.  Like it had straight pipes.  I did see a lot of dust blowing over the rear driver side tire. After about a minute or so it was quiet again.  So I loaded and went riding.  Same thing happened and while it was loud I did get one backfire upon acceleration.   After a minute or so it was quiet and ran great for the day.  Got home and same thing.  I took off one heat shield and all my springs are there.  No visible exhaust leak.  Couldn't tell if the valves were noisy or not. 
Any ideas?

There are two sets of spring joints. Check both and check spring tension. Very common for the springs to weaken and the joints to move apart enough to break apart and blow out the seals...and you wouldn't see it...just hear it.

My 2017 Z8 does the same thing.  It's a little loud when cold, but it seals up as it warms up.

I ignore it. Not (yet) worth the effort to "fix".

[2015 Z Force 800 53/Trail EPS]

Just to toss-in that if one of these exhaust leaks is close enough to the head to allow the pulled-in cold air against the valve stems during overlap, it can warp the stem(s) and bind it in the guide. Once that happens the valve isn't fully closed when the piston reaches TDC and impact occurs. These spring joints are far enough away for that not to happen...usually..but if the leak is at the head to pipe gasket...it can and most likely will happen. Worth making darn-sure IMO.

I'm trying to understand what you wrote as it is not clear to me.

Are you suggesting that the head metal is not a sufficient heat sink to keep any exhaust leak from unevenly heating the head components during warm-up?

My 2017 Z8 does the same thing.  It's a little loud when cold, but it seals up as it warms up.

I ignore it. Not (yet) worth the effort to "fix".

Oddly enough, mine seemed to be louder but I guess I just kinda learned to accept it.  Until I investigated and realized that gasket was completely gone.   Then I spent the time and money and fixed it.  Back to quiet again.

You getting popping on decel?

[2015 Z Force 800 53/Trail EPS]

I'm trying to understand what you wrote as it is not clear to me.

Are you suggesting that the head metal is not a sufficient heat sink to keep any exhaust leak from unevenly heating the head components during warm-up?

Not at all. It's just that the exhaust gasses flow across the exhaust valves..and stems on their way out and they get very hot of course. If cold air is pulled-in against them, that sidemaking contact with the cold air will contract, warping the stem and depending on the amount of warpage, can cause the stem to bind in the valve guide when closing. If it is not fully closed during one stroke, there is the possibility of the piston hitting the stuck valve(s)...and that's the end of the engine...or at least the top end. During overlap, that's when the piston is at TDC of the exhaust stroke, both intake and exhaust valves are slightly open at the same time. This is for proper scavenging but for a split second there is a sight flow-back from the exhaust system. If that flow happens to have a stream of cold..as in just ambulant air.. with it, it can..not always.. effect those valve stems depending on how hot they are.

In short it's just a good idea to fix exhaust leaks..just to be safe. The other thing I wanted to say is that when I was taking pressure readings on mine before doing my exhaust mod...and this was about the time when I too have some spring joint problems, with all sealed and the spark arrester installed I was able to get a ridiculous 4.2 psi reading at 6200RPM and at WOT. I expected ounces..even something under a pound but not over 4psi. No wonder those spring joints get pushed apart! With the arrester out that was cut to 2.4psi but it was so lean it didn't run right in normal operations. I added an HMF arrester and it was then borderline but did loose some low end. Now that I have the OE arrester back in and adapted to the new end I did loose some top end power but gained back all the lost lower end so...that cool with me...and it's a little quieter. 

No popping on decel.  It runs great after a minute or two. 

I get popping on decel when it's cold, maybe for the first minute of running.

Clark,

I guess I'm just trying to understand where the cold air would come from getting sucked into the exhaust side. I'm sure I'm not understanding something.

[2015 Z Force 800 53/Trail EPS]

I get popping on decel when it's cold, maybe for the first minute of running.

Clark,

I guess I'm just trying to understand where the cold air would come from getting sucked into the exhaust side. I'm sure I'm not understanding something.

The donuts...or spring joints on these are far enough away that even if they did leak they won't get to the valve stems.. but where the gaskets are on the exhaust head flanges...where the pipes bolt to the heads...they are close enough. If you ever have one of those blow or leak...fix it.

Got it. Thanks!

I had 2 out out of the 3 donut gaskets blow apart recently. Loud, you bet.

Replaced some springs with extras I had from a snowmobile build.  Noise is gone.  Springs were thicker in diameter and shorter in length

Hey guys if you see this where did you source exhaust gaskets? I will search on the Internet now .... but curious .... my 500 is developing the backfire on decell, engine braking ...

[2015 Z Force 800 53/Trail EPS]

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