I am doing some service on the bike and found a thing on the bike that I have never seen before and I wonder what it is for?

On the rubber joint that connects the throttle body to the airbox there is a small plastic box that does not lead to anything.




You can see it on this picture from KEV where it sits on the top of the joint.

And also in the parts manual it is not described at all. Even in the Service manual it is not mentioned at all.



So does anyone know what it is? I guess it is a resonance chamber? or a preparation for some kind of fume recirculation for places with strict environmental rules e.g California.

I think it would be ok to remove it as the stage 3 airbox does not have it and neither does the XT660Z. And just plug the hole.

It is, as you suggest, a resonator.

It has two functions: Firstly silencing, but mainly to equalise pressure waves and the harmonics on the intake side of the throttle body. When the moving column of air in the intake hits a closed valve there is a sudden compression as the air is compressed and bounces backwards. This causes pulses, or resonance. The result is a temporary clogging, or high pressure area in your intake tube that can limit airflow.

Adding a resonator forces air bouncing back to collect in the chamber, slowing the backwards pulse and equalising pressure. This then allows fresh air to flow towards the engine from the airbox without it having to fight against the reverse pressure wave.

Theoretically adding an intake resonator (air chamber) makes the engine quieter and more powerful.

The physics is of course a lot more complicated than this, but hopefully it gives you some idea of it's purpose.

Interestingly the Z doesn't have one, but that could well be due to the different design of airbox meaning that intake noise, resonance or back pressure are less of a problem?

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I wonder if removing it would cause a loss of power when using a stage 2 filter setup. Probably not since a lot of restrictions have been removed and thus making the resonator obsolete.

But on the second hand it is not obstructing anything and the weight is negligible.

If you want my honest opinion, I really don't think removing it would make a huge amount of difference either way. Probably best leaving it alone.

The DNA stage 3 airbox (in fact it isn't an airbox at all really) on the R/X will have completely different resonant characteristics from the stock airbox and therefore does not need a resonator.

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So when doing my service I decided to remove the resonance chamber from the manifold.

Here is a picture of the box itself when removed:



I found a plastic plug in the garage that had the correct diameter as the hole:



I trimmed it down both to fit the hole and also the length of so it does not interfere with the airflow:



After that I but a strip of gaffa from the inside of the manifold and filled it with hot glue:



Before the glue settled I put the plug in and afterwards I removed the gaffa strip from the inside.

Here is the end result:



So now I have got a induction path to the throttle house that is smooth without any obstruction and also some less weight.

Mostly I have done this because I hate stuff on the bike that has no use and take up weight and space. If it will make any difference to the performance in any direction I do not know. But since I have a stage 2 filter and drilled airbox with the snorkel removed I think that the resonance chamber is not needed.

Did removing the resonance Chamber have any affect on performance or sound at all in the end??

Yamaha called them boost bottles...
were first seen on the YZ motorcross
& IT Enduro bikes early 80s..




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Harley Davidson..
The easyest way to turn gasoline into noise with out the side efect of horse power...

A boost bottle is completely different kettle of fish altogether. They are/were mainly (but not exclusively) used on 2-strokes and are fitted between the carb (or throttle body) and the engine's inlet port (in the inlet manifold or intake tube). The Yamaha boost bottle was known as YEIS (Yamaha Energy Induction System). The theory is that, even with a reed valve, some air/fuel mixture will end up flowing back in pressure waves towards the carb when the piston is in certain positions and ports are not completely open or closed, so the extra volume provided by the boost bottle (YEIS) absorbs some of these pressure waves and evens out induction. This back flow of fuel/air mix causes richer than ideal running conditions and power losses. Power gains can be had as a result of adding a boost bottle on a 2-stroke and where the power is gained can be pushed higher up or lower down in the rev range depending on the volume of the bottle. The YEIS system was set up to improve (or boost) low down and mid-range power and torque when a 2-stroke is least efficient (out of its power band).



The XT resonator is upstream of the throttle body and is there just to even out the pressure waves in the air flow, and the main reason for this is silencing induction roar on a big 4-stroke single. It makes no difference to power at all.

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My Z seems to have one. A hose runs to it from the air box, mounted under the intake rubber instead of on top?

I think the 'bottle' you are refering to is the crankcase breather chamber? Aside of the intake hose, there is only one hose between the throttle butterfly the and cylinder head and that is the intake air pressure vacuum signal (which you can't see in your picture as it connects at the top of the throttle body and runs off to the IAP sensor under the tank).

Here is a breakdown of the hoses in you photo:

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