Airflow Vs CO setting.
 

Okay I've read as much of the threads I could, but I guess the relationship between air-flow, fuel, co2 adjustment and surging is not completely clear to my uneducated brain.

As I understand, this bike runs lean, but also needs more air. More air results in an even leaner bike, so the CO must be adjusted up to increase fuel richness. CO up = richer fuel = good.
The surging is related to this lean/rich/better air-flow equation.

What I want to achieve is more power in the lower gears at lower revs - the gap between 2nd and third is sometimes inconvenient, 2nd being quick to rev too high and 3rd not having enough revs to take over the job.
I'm not really interested in top-end gain.

Here's what I am doing - I have removed the snorkel and intend to drill two holes in the sides, and install a dna filter.

The response seems better for the snorkel removal, but the CO adjustment is a much more elusive trick to master.

So far I have increased Co from 5 to 13. I still experience a snatchiness in certain rev ranges, though I'm still not sure if it's an improvement or the same as it was. Given I've increased my air flow slightly, doesn't that mean my air/fuel mixture is more or less as it was before?

Will adjusting UP, in theory, decrease my surging? Can *overadjusting * the co increase the surging? How do I best find the sweet spot? I had it at 20 (15 above) and it seemed snatchier, but maybe I was imagining it.

When I do install the new dna filter and/or increase the air flow with holes, will I need to adjust up again or should I leave it?
How will I know if the bike is too lean?

Why does increasing the airflow past a certain point (stage 2) make the co adjustment no longer effective and I then need a fuel mod?
Why does the co adjustment not compensate for the extra air flow -
and isn't that what an EFI system should do automatically anyway?

If I do get a fuel mod, will I need to put the co back to what it was otherwise it will be over-rich?

It's a bit annoying it doesn't do these things automatically and has to be tricked into doing what we want it to.

Raise the bikes CO with only airfilter will not solve the problem, cheap but not good at all. Plug the AIS and buy/build a fuelmod. But the best is to buy a power commander to be able adjust better with a dyno.

Skickat fr�n min GT-I9295 via Tapatalk 2

Adjusting the CO will only alter the fuelling slightly and only at tick over and very small throttle openings (up to a TPS reading on 18 I think?) The CO setting has no effect on the fuelling in the rest of the rev range at all.

Don't drill holes in your air box and/or fit DNA filters and expect the CO adjustment to compensate for the extra airflow.

As Landton suggests, you need to fit a Kev Mod or a Power Commander to get the air/fuel ratio set correctly for any air box mods.

BTW - What year is your XT and does it have an O2 sensor?

You must go one step at a time and always note what you have done, so you can test and then return to the starting point if required. Bike tuning needs a steady hand and alot of patience. You are starting with a bike that needs attention cos it is a big single tuned by Yamaha to overcome the European regulations for noise and emissions which creates a very poor riding machine that CAN however be dramatically improved fairly easily and without too much expenditure.

So follow the threads, read everything, ask loads of questions and take one step at a time. Have fun!!!!

Bike is 2006, xtx, (though the frame identity calls it an xtr).
I'm not sure on the 02sensor. That is the 'lambda sensor' in the exhaust? It might not have one.

I've tried to find the AIS, but it eludes me and there's no clear photo on the site. There's 3 potential locations on the manual diagram -
9. Air filter case breather hose
10. Pilot air hose
11. Air filter case to air cut-off valve hose

But nothing that says 'AIS' hose.

Looks like I'll have to just spend the money on a kev fuel mod after all.
Do I just hit the paypal link or do I need to contact him first?

You haven't got an O2 sensor if it's an '06 bike, so no worries there.

Have a read of this thread...

http://www.xt660.com/showthread.php?t=5544

Kev's posted some pictures which will help you identify the AIS pipework.

Hey Strelm,
The Kev fuel mod is pretty cheap (for the results it gives) and easy to install - so I definitely recommend that option along with the DNA filters. You'll get a total different feeling bike from these relatively easy mods. But also, if you want more bottom end power, you could change your gearing by putting on a bigger back sprocket or small front. A 47t rear sprocket made a world of difference to my bike. Again pretty cheap to do in the scheme of things.

I have no idea why you'd need to block the AIS - especially if you've got standard pipes. That doesn't translate into power gains as far as I understand - just stops it popping so much.

And yes I agree it sucks that you have to mod the bike at all as it should be right straight from the factory. But it is fun to tinker...

I wouldn't mind getting rid of some popping, I know there's not a power gain or anything.

So according to the pics in that thread, in the service manual the AIS is the pipe called 'air filter case to air cut off valve hose'. It's a 2004 manual, hope it still applies.

Also in that thread I found a statement on the co setting that puts it in perspective (though others may have said the same)
So really there's not a lot it will achieve, though better than nothing. I guess with the throttle mod that helps.

Fuel mod and new filter on the way.

And yes, it is kinda fun to tinker. :)

Thanks all.