I have just installed a K&N Filter witht the Prefilter over the filteron my Rancher.(It looks like just a bag over the filter). I had this setup on my 300 4x4 and I ended up taking the prefilter off the filter because the bike wasn't getting enough air and was bogging. When I took it off the bike worked great with more power. Now I have it on my Rancher and I think it starting to do the same thing. What is it for? Do I need the prefilter?

 

By prefilter I assume you are refering to an OUTERWEARS??? K&N claims a 10% reduction in airflow when running the prefilter. For me (I live in the dusty desert), I would NEVER run without the prefilter.

Did you not bother to rejet when you installed the K&N?? Sounds like all you need is a simple rejet for the change in airflow.

 

I do not live in a very dusty climate, just in the middle of the summer on back roads. What do you mean by rejetting?

 

Rejetting-You carburator has to have the right ratio of fuel to air. If it has to much fuel, it will run RICH (the spak plug will be black and your tail pipe will be black and sootey). If to much air, the it will run LEAN (spark plug will be gray, motor runs hot and can damage your engine). Anytime you change the airflow into (or out of) the engine, you have to change the size of the jets (little holes where the gas sprays from) in the carburator to restore the right ratio of air to fuel. And, check your spark plug. It should be a brown color on the electrode tip, if you are properly jetted. You can also change the height of the jet needle (it's getting complicated, huh). Get a service manual, and it will describe how to change the jets if necessary or take it to a dealer. Jetting is ART NOT SCIENCE, and should be done by someone with experience!!! There are some articles on jetting out there. I will try to find you a reference.

You situation sounds weird! When you put the K&N on (without a rejet), you should be running lean. Just adding a prefilter, even if it cuts your airflow by 10%, should still leave you way leaner compared to a stock filter. It doesn't make sense!!

The stock airfilter is pretty restrictive. But, on the Rancher, the air intake (snorkle) is pretty restrictive too. Possibly, that is the limiting factor in your airflow, not the filter?????