Vintage Dirt Bike Q & A

I know with autos the K&N filters give a performance gain, but does the same hold for motocross bike? I now run a Uni-filter, but was wondering if using a K&n was worth the switch? Thanks.

J

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#829 The "Factory Novice"

1988 Honda CR250RJ
1983 Honda CR480
1981 Can-Am 250 MX6-B
1979 Honda CR250RZ
1979 Kawasaki KX250 A5
1978 Husky 250CR
1978 Honda CR250R
1977 Yamaha YZ400D
1977 Suzuki RM125B

I run both. I have a large and long K&N with a somewhat open cell Unifilter over it. Bear in mind here that I do not run the stock air box. In fact I don't have an airbox at all. Just the K&N clamped onto the carb with a junk of pretty hard rubber between the carb bottom and the case to prevent the carb bouncing around and tearing the intake manifold rubber off.

I could take a picture of it if you want.

Loren

K&N cost me 11 pistons, 6 rotory valves, a crank, sleeve... on a 1974 Can Am T'NT 125. 274 miles on a new bike and the piston skirt broke off. Half of those miles were on the street.
When I bought it new the shop had put a K&N on it because someone wanted to buy a spare stock foam filter.
Long story but if you like your dirt bike, don't put a K&N on it. They cost me $1100 in two years for repairs on a $999 bike.

Hi Rick,

Were you finding more grit inside with the K&N or???

I went with the K&N mainly because I machined a whole new intake to get a better angle into the crankcase and it tilted the carb up so it no longer fit into the stock housing. I also have lots more area and even with my double filter setup I *think* I'm getting better airflow. (Don't have a flow meter so it's more of an edumacated guess.)

I use the K&N spray on filter oil for the K&N and then Belray foam filter oil diluted 50/50 with gas on the foam filter.

Loren

After my second piston broke I bought another K&N. I had no idea they came with a foam filter as this bike was robbed of it's original before I bought it and I got no owners manual. I ran 20 miles, changed filters and another 20. Cleaned and oiled with K&N cleaner and oil. Greased the threads where it screwed on... Same problem. 270 to 400 miles and the piston skirt broke off on the intake side and many times the rotary valve was worn on the leading edge it was razor sharp - literally. This was on a bike that was the most reliable dirt bike/enduro bike built to date.
When I finally figured it out I went over 3,300 miles in all dirt and did a tear-down with almost no wear.

Silt passes through the fibers. So, the quick solution is to run a foam wrap. Why not just run a UNI? Less restrictive than two filters in my opinion.

Quick test: Take off your K&N and run your index finger in the bell of the carb. If you have ANY dirt (silt or film of brown color) it is passing dirt and your intake skirt will likely break off. Use a Q-Tip if necessary as the contrast is better with the dirt on white.

I am probably K&N's worse customer but I have $1,100.00+ in bills and so much down time (before UPS and FedEx times) so I will continue to steer people away from their product. Even their new products pass silt, I have a Banshee I bought that wore out in about 40 hours. It hooked a ring on the exhaust port due to excessive wear. That is uncalled for in todays times.

Hey J,
Your using the best air filter on your bike, there is no comparing a paper filter to a foam filter. If you want more protection from the single stage, we carry a dual stage Uni air filter. We have never had a problem with Uni filters. They are the best filter on the market for these old dirt bikes.

Don