Vfr 800 1998 running rough

I put a k&n air filter on my bike about 6 weeks ago and all seemed well. Slightly noisier air box and that was all. Lately though it feels as if the bike is slightly slower on the up-take under 6000 revs, after that seems fine. Also I feel the air box is louder and the engine didn't seem to be as smooth as it was before the air filter was fitted. Any ideas or is it just the different flow rate of the filters. Many thanks .

 

Sounds like some time on a dyno is in order,I recomend you think about investing in a DYNO JET Power Commander,it allows more precise fine tuning of the ignition and fuelling,will give you a little bit of a power boost too when its set up right!But definitely get it on a DYNO for a better diagnosis!

 

I've got foam glued in my stock element that flows more than a K&N and I don't have any problems w/ stock tune and exhaust. If it was fine and getting louder/running worse something is up. Maybe the airbox lid is leaking and needs refitted? Maybe a vacuum line is pinched? I'd throw the stock filter in and see how it reacts. Pop a spark plug out and see if it's running rich or lean.

 

I have heard that any alteration to the air or exhausts can cause this sort of problem, also I replaced the fuel filter just before the air filter so I may have pinched a breather, I'll lift the tank an have a look. Thanks

 

I had problem once with putting too much oil on the K&N filter in my car once (a Mazdaspeed 6). The car ran good at first with more intake noise (I think that is normal) but after a week or two it started running rougher. When I took it in to the dealer for its service appointment they noted the rough running and said it was because there was an oily build-up on the mass airflow sensor grid in the intake. They took the K&N out for me, cleaned the sensor, and installed a factroy filter and it ran fine. When I got home, I washed the K&N filter and re-oiled it once it dried completely. I put less oil on the filter this time. I sprayed it lightly till it turned pink, let it sit for about half hour, and then resprayed any areas that were still white. When I re-installed it in the car after this, the car ran fine. Long and short of the story, maybe there is a bit too much oil on the filter. Try cleaning and re-oiling the filter and see if that helps.

I also have a K&N filter in my bike (a 2000 VFR and the K&N was fitted by the previous owner) and although the intake does seem a bit louder (not really noticeable at idle or low speed, but a bit noisier under heavy acceleration) compared to the stock filter (previous owner gave me the stock filter as well, to use when cleaning the K&N he said) , but the bike runs fine. My bike also has a Delkevic 18" slip-on exhaust. Previous owner installed the K&N just after he bought the bike he said and never had a problem with it running poorly. Currently 66,000 km's on the bike and she runs like a top.

 

Durk could be right, it might be a vacuum line issue.

Secondary air intake can cause vortexes in the air box if it is open below high air flow, meaning below about 5k rpm. It is controlled by vacuum line and a valve on the right front side of the air box, and it is actuated by a diaphragm on top of the airbox. Normally it should be closed till about 5-6k rpm (when trans is in gear that is, not on neutral), and above that it opens up for more air flow which is needed.

 

I've lifted the tank slowly and no pinched lines, inspected the filter housing nothing seems wrong. Also took the air filter out and no excess oil, all clean and tidy. I'm going to replace all spark plugs as I've done just over 10k miles and never even looked at them! The bike is on 22k miles and could well be the originals. As I ride the bike every day I have noticed the difference from how it was but others that have ridden it say its fine, although the ride in-line fours. Thanks, I'll let u know how the plugs go.