Vintage Dirt Bike Q & A

What's the trick to installing the air filter and cage into the airbox of a 1980 CR250?

Stock?

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

yes a stock Honda foam air filter. How do you get the cage and filter into the airbox and properly secured. Do you have to unbolt the triangle flange to install it?

I haven't had to deal with this yet since I am up to my armpits in my '79 resto, but both bikes have the
same airbox and mounting problems.

Remove the mounting flange (the gold chromate colored piece) mounted with three bolts and install the
airfilter over the plastic cage and mounting flange and secure it with the metal band. Then install the
assembly back in the airbox and reattach the inlet rubber. The frequent removal and reinstallation of the
mounting flange is why Fox produced a one piece backing ring back in the day. The backing ring prevented
the holes in the plastic airbox from being "hogged" out. You can still get the ring today as a reproduction.

Another option you might want to consider; Twin Air makes a one piece filter that is designed to
circumvent this mess by including the cage and inlet rubber as an integral assembly. You remove the
mounting flange permanently. When you install the Twin Air filter, simply remove the airbox cover, put
the Twin Air filter in the box attaching the already mounted inlet tube on the carb through the existing
hole in the airbox. Put the airbox cover back on and you are done. That is what I would use if I was
building a rider/racer.

dogger

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1973 CR250M
1979 CR250R
1993 CR250R
2008 CR500R
2009 CR250R

...to add to what dogger said:

The air boot mounts permanently to the gold metal plate. You should seal the air boot junction with silicone. The black plastic cage goes in the metal plate, the filter goes over the cage and plate, and then you slip the whole assembly into the air box and wiggle the air boot onto the back of the carb. Hold the assembly in place with one hand and line up the holes in the plate with the holes in the airbox and then do the nuts up loosely with the other hand. The rubber piece on the stock filter means you can get a good seal between the plate and the filter. You may struggle to find the NOS air filter clamp. If so use several narrow (<9mm wide) hose clamps end to end to make one band long enough. The Fox plate is a real good idea. Note that the air box only comes out of the frame forwards with the engine out. I seem to remember that the air boot on the Twin Air is smaller than the hole in the front of the airbox so it wasn't clear what would stop it flopping around some. Stay away from Uni Filters.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF