Installed K&N Air filters, performance changed

[VstarAl]

I have an '07 Venture, 25k miles, stock engine/exhaust setup, carbs settings have never been modified (except being balanced a couple of years ago). A few days ago I changed the spark plugs and replaced the air filters for the first time. Instead of installing paper filters, I installed K&N filters. After putting the bike back together and taking it for a test ride, I noticed a (somewhat negative) performance difference. When accelerating through gears 1-4, or if I cruise around 40 MPH in 4th gear, there is an occasional sag. Overall, the bike still accelerates well, but the sag is more prevalent when holding a steady speed. Highway performance is good; cruising at highway speeds is smooth, and passing is no problem. Also, when decelerating, there is more popping, and an occasional backfire (when decelerating from highway speeds). The bike has never backfired before. Mileage is still around 40 MPG (I rode over 600 miles since the plugs/filters were changed). I thought the K&N filters were a direct replacement and no carb mods would need to have been made. Has anyone experienced this before? I still have the paper filters, and when I make time, I will put those back in and see if the performance goes back to the way it was.

 

Any other suggestions on what I could check?

 

Thanks!

Edited August 3, 2012 by VstarAl

[M61A1MECH]

I had a similar experience when I put K&Ns on my 07, but I also opened up the air boxes at the same time, I had to reshim the diaphram needles, aded one shim to each diaphram and that cured it. See this thread in the tech section, about half way down and you can see what I am talking about on the shims.

[JerryK]

Make sure you are running on all cylinders and didn't drop one. You can be running on three and have the things you are. Lightly touch the back of each exhaust and make sure they are all hot. A few years back on a 2000 Venture I had I ran through some water and lost fire on one coil and didn't notice much difference till I found I was running on three after a few days. Could be bad or cracked plug... easy to check by touching pipes.

[VstarAl]

Thank you for the replies/ideas.

 

After running the engine for a bit, all of the exhaust pipes leaving the jugs felt hot, so I believe all four cans are popping.

 

Here's an update: I took out the K&N filters and reinstalled the stock air filters, and the sag/pop/backfire issues went away. I sent an E-mail to K&N asking them where to go from here. I went with the K&N filters because I figured they would last the lifetime of the bike. But, I do not want to modify the airbox/carbs just to get the K&N filters to work!

[XV1100SE]

My dealer didn't have OEM air filters when I wanted to do my 25,000km tune up. They did have the K&N. I've had no issue with them at all.

[twigg]

If you ruled out other problems by swapping the filters back and fixing it then you have two choices.

 

You can run with paper filters, or you can fix the fueling issues created by more air through the free flowing K&N.

 

As standard, a change to K&N shouldn't require re-jetting. But you are getting more air in, and if it was running marginally lean, you just leaned it out more, hence the issues.

 

You may have an air leak that was not causing a problem until you introduced more air.

 

Raising the needles should restore the balance, because that will let in more gas, but it isn't a cure for an air leak, it's just a disguise.

 

Eventually you will have other issues with a rough idle, or a high idle being favourite.

[gibvel]

Wondering if he has to adjust the needles. He says highway speeds are good but 40mph in 4th is fairly low on the RPM range and can't be much main jets going on.

 

Have the carbs ever been worked on or are they stock, including the idle mixture screws, from the factory? Have you even set the floats?

 

The bike is set to run lean from the factory and some have found that the floats are quite off as well which could add to the lean condition. Then putting the K&Ns on just leaned it out more.

[M61A1MECH]

I am sure that all it needs is to reshim the needles, but his last post said:

 

But, I do not want to modify the airbox/carbs just to get the K&N filters to work!

 

The bike is set to run lean from the factory with paper filters, if you change to filters like K&N that flow more air, the bike is going to be even more lean, some something has to be done to the bike or the paper filters need to go back in to get it back to the factory set up, well that is how I see it any ways.

 

Unless the filters are not oiled properly I am not sure what else could be done.

 

Reshimming the needles is not a big deal and only takes about 30 minutes.

[RSTDdog]

Before condeming the KN filters, check for air leaks in common areas, the little rubber boots over the ports on the intakes (where you hook up to sync carbs comes to mind).

 

As mentioned before, are they oiled properly? a dry KN filter or one with insufficient oil will be considerably leaner. Also if it doesn't have enough oil it will pass dirt.

 

Per your first post, Last time your carbs were balanced was a couple of years ago? what is that in miles? With new spark plugs and new air filters another carb sync is also in order.

 

Double check that all your plug wires and boots are fully seated as well.

 

Also check the clamps on the mufflers where they slide over the head pipe and make sure they are snug.

 

Let us know how you make out.

[ACE50]

I wouldn't suggest to anyone to use K&N's if they weren't willing to tune the bike for them. They will lean the bike out on a possibly already lean condition. These engines love to breath but you have to maintain the proper air/fuel ratio when you change things. I'd first plug or get rid of the AIS. That alone could get rid of the backfiring but you'd still should do some adjusting as shim the needles, adjust the pilot jets. Better yet, larger slow jets (17.5) as you can still adjust them down with the pilot screws if need be and check the floats. When done correctly, you'd hardly see a change in MPG and have a better running bike.

 

The whole idea of a lifetime filter seems funny to me as most people do not keep there bikes for it's lifetime! After a few years they move on to something else or even stop riding. That's why there are so many older low milage bikes on the market all the time.