Exhaust popping on stock bike
 

Hello XT forum.

I have a new to me 2013 XT660X that is completely stock and has gone 7800km.

However, the exhaust is popping like crazy especially when slowing down. Is this normal or is it possible that there is something wrong? I dont remember my old KLX250 having this problem.

Thanks :)

My standard 660z pops like corn in the microwave

TADTS :BaseballHat_LNY2EG:

Blocking the AIS pipe reduced the popping on my Tenere, it's worth trying.
http://www.xt660.com/showthread.php?t=5544

Don't close the throttle completely. I think its the unburned fuel escaping.

The popping and backfiring is perfectly normal. It is (as Jaques says) unburnt fuel igniting in the exhaust when the throttle is snapped shut.

On older bikes (with carbs) like your KLX the fuel wouldn't ignite (unless you had a leaky head/downpipe gasket) as it is starved of oxygen and would just pass out into the atmosphere unnoticed. Current emission regs mean that unburnt hydrocarbons in exhaust gases are a big no no, so air is deliberately introduced to the exhaust port downstream of the exhaust valves to make sure any excess fuel is ignited and burnt off.

On the XT this is known as AIS (Air Induction System) and an ECU controlled valve opens to let air into the exhaust from the airbox to burn off excess fuel when the throttle is suddenly closed. It also opens on a cold start to clean things up as the engine runs rich, and also to speed up the warm-up process as the head, exhaust ports and system will get hotter quicker because of the fuel igniting in them.

AIS is important if you have cats fitted (stock exhaust system) as unburnt fuel quickly damages the catalyst.

If you don't like the popping effect of the AIS (and you don't have cats) then you can simply block or clamp the pipe to the AIS valve that runs from the airbox (or remove the whole system altogether). You cannot just unplug the AIS valve under the tank as its default position is 'open' and the bike will pop and bang all the time!

I blocked mine for Dyno testing (messes with the test results) but then unblocked it the other day.

Shotgun!

Sounds awesome!!!! Well at least until you get an aftermarket exhaust... My Barrett single sounded like gunshots going off...fun but a tad disconcerting!

Blocked my AIS port and removed the valve entirely.

Mat

Thanks for the feedback guys. I still have the stock exhaust with the cats, so I will have to live with the popping for now. Maybe I will go aftermarkets later but the only system I really like is the OTR 2-1 Akrapovic and its super expensive, not sure I am willing to fork out the money for it, hehe. :)

Have a read in the linked thread, as you don't have to put up with it despite still being all stock.
You have the choice of blocking the intake air from the air box or you can block the air at the port near the exhaust.
Either way you go, it matters not if you are on stock pipes or aftermarket.
Matt

Yeah I saw the thread on blocking the AIS, but Pleiades said that it could damage the catalysators.

Is there something I understood wrong?

Exhaust popping on stock bike
 

If you block the AIS, the catalyst will get damaged by the unburnt fuel.

However, in most countries motorcycle emissions are not tested, so you can block it and it doesn't matter if it gets ruined or not. It is up to you. If you don't like the popping then block the AIS - the bike will run fine. Just bear in mind that the catalysts may not work as well, if at all as time passes.

Yeah I know in Denmark where I am from they dont test ****. I was riding a big bore KLX with all emission stuff removed and no one gave a ****.

However, I have now moved to Germany and they are more strict here and I am not 100% certain what they test for so I will keep it all stock for now. I was more worried that there was some kind of issue with the bike, but since this is apparantly is fairly normal I wont bother doing anything.

Thank you all for your feedback. :)

Thanks for that info. I've just bought a 660Z in Australia modified by Yamaha on promotion. It has a Barrett single on and I don't appreciate the very loud popping. I'll be getting it in May when I visit my kids, and make sure I take the necessary to block the AIS pipe off.
My 660Z in South Africa has twin Scorpion pipes and with baffles in they are at the edge of being too loud with the popping. But so far I've persevered with it.

Hi dirkz, when you say your scorpion system is nearly too loud....is it horribly loud or just right. ? It's the system I fancy for my Tenere. Is it a system you recommend. ? Thanks Steve

This is why, although you can block the AIS with the stock system, it is always worth mentioning the effect on emissions and the catalyst. In some countries, and I'm pretty sure Germany is one (Switzerland is another), your bike will fail it's roadworthiness test with the AIS disconnected or blanked off and a non-functioning cat. Always worth checking your country's specific regulations before doing some mods - they aren't all the same.

In the UK, like Denmark, no ones cares about motorcycle emissions once the bike has passed initial type approval, unlike with cars and commercials. Emissions testing for motorcycles is on the cards for all EU countries in the near future...

Love the sound of the Barrett with the AIS blocked and one diffuser in the pipe.
Barrett supply two options for Db killers one is just perforated mesh and the other is a tube a few cm long that has two perforated mesh plates on each end.
I found it too quiet (for me but actually really pleasant) with the double section in and the single plate doesn't sit too well due to the angle of the cone as it exits the pipe. So to ensure it sits in solid I use the pipe baffle but I ground down one end to remove one of the baffle (perforated plates) ends. Now it sits into the pipe and doesn't move at all and has basically the exact sound of the single plate.

All I get now is a nice bark up the rev range if I wrap it on hard and a nice burble at highway speeds, all very deep in tone and not high pitched like the big sportbikes. You still get a pop occasionally on decel, not as much as I would like but I guess its waaay better than the gunshots I was getting with pipe and AIS functional.
Matt.