Why do Yamaha fit the AIS in the first place? What's it's purpose?

I think I'm correct in understanding that when the engine is on the over run with a closed throttle it is to let air through to weaken the fuel/air mixture. With the AIS opening there would be a rich mixture, so it's to balance the mixture??

Will there be any long term damage if the AIS is permantly removes either with the original lamba sensor and cat or without them by running an aftermarket exhaust? Surely Yamaha don't fit the whole assemble just to make the bike pop?

The AIS is purely an emission control device. Yamaha have to fit it to the XT660 to comply with exhaust emissions in the countries where it is exported.

The AIS has no influence whatsoever on the air/fuel ratio (mixture) as the air is inducted after the exhaust port - it never enters the engine, fuel or intake system at all. The purpose of the AIS is to provide additional oxygen (well air) to ignite any residual unburnt fuel left in the exhaust after the throttle is rapidly closed. The valve also opens when the ECU senses certain other running conditions such as at idle and on a cold start.

You are probably best advised to keep the AIS connected and functioning if you are running an exhaust with cats (whether stock or aftermarket). Catalysts can be destroyed quite easily by fuel vapur and unburnt hydrocarbons, which is another reason why Yamaha fit AIS to thier catalyst equipped bikes. If you are running aftermarket cans with no cats, then disconnecting the AIS will be fine.

The only side effect I've ever noticed about disconnecting/blocking the AIS (apart from the lack of back-firing) is the bike appears to take slightly longer to warm up in the morning. This is probably due to the fact that the AIS valve would normally be open for a cold start allowing air to ignite excess fuel in the exhaust port/header, which in turn helps provide some extra heat back into the head. Also a hot exhaust will flow gas better than a cold one.

that's answered my questions Pleiades, it all makes sense, good answer, many thanks

Bit late to join the thread-

I've blocked my pipe and am certain its the correct one. However I still get a very quick succession pop whilst slowing down with the throttle open just a tad. Also could have just been a cold engine as I didn't warm up before I took off at all, but it felt quite flat at certain low rev ranges, any ideas?

Can you post a photo of the pipe you've blocked? You might have the wrong pipe - it's happened before! ;) Also it might not be completely blocked?

There's a clue in the bit I've underlined as to the "flat" feeling. On a cold start the AIS valve is fixed open to help speed up engine/exhaust/cat warm-up times. I found that with the AIS blocked the bike tended to take a little longer to warm up and felt a little more sluggish for longer until up to temp.

How did the "fuel tap" mod turn out?
 

Looking to block the ais pipe on my 2011 660 Tenere. What size is the hose in mm and what kind of ball tap did you fit? It seems pretty cramped in there. Looks really good however, and practical for those roadside emissions controls.

Hello

I did not fully read the post and not closed the correct tube .

I blocked that tube and have a little oil on all sides. Drove so for 3 days .

and I have become like the original and the bike pulls no oil. You will have caused a serious problem?

Do I have to look if something was wrong ?

Hi Guys,


here is a very easy and cheap solution for the XT660Z Tenere:


XT660Z Tenere (AIS) Air injection System, exhaust popping fix



https://www.youtube.com/watch?v=-2mTVTv5Jl4&app=desktop