CRF50 AIR FILTER / CRANKCASE VENT

BREATHE A LITTLE EASIER

TECH TIP: I gathered up all the electrical wires, bundled them together and tucked them up inside the protective rubber boot. This made for a better looking setup and protects the wiring from dirt and moisture.

TWIN AIR CRF50 AIR FILTER

SERVICE MANUAL

Hose attached to crankcase.

Hose attached to seat stay. Filter attached to end with clamp.

Hose coming up through the motor mount.

K&N Filter Care Kit - ($13)

TWIN AIR

Filter Oil

($18) 500ml

ENVIRONMENTALLY FRIENDLY

K&N Filter Oil - ($8)

TECH TIP: You may need to “richen” the fuel mixture a little when using a less restrictive filter than the stock unit because a larger volume of air will be entering the carb. I will be adding a detailed article about how to adjust the mixture in the near future.

Our first effort at increasing performance centered around getting the motor to breathe a little better. The stock Honda CRF50’s air filter box has a tiny inlet that is very restrictive.

AIR FILTER: K&N ($25)

We decided to put a K&N air filter on. The first step is to remove the stock air box by removing all the screws holding it on. Also remove the crankcase vent hose (see section below about installing a new one). Gently remove the air box being careful not to get dirt in the carburetor.

Carefully clean around the carb inlet. Apply a little filter oil around the carb flange and slide on the new (oiled) filter. Tighten down the hose clamp snug enough so the filter doesn’t turn but not too tight. You will need K&N Filter Oil and Cleaner ($13) to maintain the filter.

This modification made a subtle but noticeable difference. The bike definitely accelerated a little better and revved a little quicker. When combined with our future pipe modifications (see pipe section) the difference was even bigger.

I recently bought a TWIN AIR Filter ($25), Oil and Cleaner as an option because it is what the factory Honda team uses. We haven’t tried it yet but we bring it to the track with us. Since it’s a foam filter it should be good for very wet conditions. NOTE: The Twin Air filter oil is green and will change the color of the dry filter.

CRANKCASE VENT/FILTER: The stock crankcase vent hose is attached to the stock air box. When you remove the air box you have to vent the crankcase somewhere else. To vent the crankcase use a piece of 3/8” inside diameter automotive fuel hose. Attach the hose to the crankcase using a small hose clamp (see photo). Run the hose up through the left side engine mount and attach it to the seat stay with some cable ties. Run it up under the rear fender and cut it off near the rear of the fender. Install an Applied crankcase filter to the end with another small hose clamp. This setup keeps the filter in a pretty dry and dirt free location. Use a little filter oil on the foam insert and clean it after each ride. See photos below.