Honda CRF250L - CCC Modifications
March 20, 2013 version

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Click pictures to supersize.

This collection of information is not intended to be used on street-legal CRF250Ls, and is similar in spirit to the Honda Closed Course Competition Mods that were published in 2004 for the CRF250X. I'll just refer to this collection as the CRFL CCC mods in the future.

I've broken the mods down as follows:
  Removing miscellaneous parts
  Modifying the stock muffler
  Installing an FMF muffler
  Quieting down the FMF muffler.

Removing miscellaneous parts - Evap canister, PAIR valve, crankcase breather hose.

busy Evap canister

The Evap canister is buried under hoses and cables in the space above the transmission and just ahead of the central vertical frame member. Start by disconnecting the hoses. Each hose is labeled on the canister body.

Right end:
  1 Tank - disconnect the end that connects to the metal tube sticking down from the bottom of the fuel tank,
  4 Purge - don't mess with the short hose that connects to the purge valve; instead, follow the longer hose that exits the purge valve and disconnect it from the intake manifold port.

Left end:
  2 Air - this hose does not connect to anything; it is a fresh air inlet - no disconnect,
  3 Drain - disconnect this hose from the canister and connect it to the metal tube sticking down from the bottom of the fuel tank - route the bottom end of the hose to the right side of the bike with other drain hoses OR along the upper right frame rail, then inboard to lay on the airbox. Add a tie wrap to keep the end in place. The hose may not be long enough for the first option.

Disconnect the electrical connecter on the top of the canister. Cover the exposed wire harness end with electrical or other tape and tie the end down with a zip tie to a nearby harness.

Unscrew the two mounting bolts from the two metal brackets.

Slide the metal brackets out of the rubber straps - difficult to do. Alternately, slide the rubber retainer strap partially off the right end of the canister; this allows the canister some freedom of movement. Remove the canister from whichever side of the bike seems easiest.

busy busy
Seal the end of the intake manifold port with a rubber vacuum cap and small clamp.

busy busy
When I installed the Big Bore Kit, I took some time to solder the intake manifold port as extra insurance against a split vacuum cap. I put the rubber cap back on.


busy PAIR valve

The PAIR valve is located near the radiator overflow tank on the right-front of the frame. Remove the right-side radiator shroud. PICS OF LOCATION. Disconnect the electrical connecter on the PAIR valve. Cover the exposed wire harness end with electrical or other tape and tie the end down with a zip tie to a nearby harness.

busy busy
Disconnect one hose from the fresh air inlet port on the top of the engine. Seal the end of the fresh air inlet port with a plastic cap and medium clamp.

Plastic cap and medium clamp - you need 3 of each; 1 here and 2 below.

Disconnect the other hose from the upper airbox port (right-front of the airbox). Seal the upper airbox port with a plastic cap and medium clamp.

Remove the PAIR valve from its mount. reinstall rad shroud etc.


busy busy Crankcase breather hose

Remove the crankcase breather hose from the crankcase tube and the lower airbox port. Seal the lower airbox port with a plastic cap and medium clamp.

Install an air filter on the crankcase tube. I used an old XR250R hose for mounting.

Note the absence of clutter in the central area above the transmission - you've removed a bunch.

Uni Filters Push In Breather Filter; 1/2 inch = 314-9855, 3/8 inch = 314-9854; size depends on hose used - about $15-$16.  Chaparral
Rubber vacuum cap 3/32 or 1/8 inch - at your local auto supply store (NAPA, AutoZone).
Small clamp 1/4 or 5/16 inch AKA Corbin clamps - at your local hardware store (TrueValue).
Plastic cap 1/2 inch - at your local hardware store (TrueValue).
The Hillman 1/2 inch plastic caps at True Value are very difficult to slide onto the ports they are meant to close. I found that the Midwest Fastener Corp 1/2 inch caps are slightly larger and much easier to mount; these are sold at Murdoch's Ranch Supply in Salida.
Medium clamp 9/16 inch AKA Corbin clamps - at your local hardware store (TrueValue).

Modifying the stock muffler

The CRF250L muffler is very heavy and efforts to lighten it will focus on removing the catalytic converter, lightening the spark arrester, and internal baffle work.

Tools used:

Dremel tool with fiberglass cut-off wheel
Makita rotary tool with bigger wheels
Vise grips
Common hammer

I cut a piece of the muffler out where I thought the catalytic converter would be - lucky guess. Then I cut out a piece of the inner pipe so I could get to the material inside.

I dug out some of the material, but it was obvious I was never gonna get the remaining material out - it completely filled the inner pipe for another 4.5 inches. When I did this to the WR250R muffler, I only had a short 1.5 inch piece to work on, and I eventually cut the entire piece out rather than try to dig out the guts. So, new plan for the CRFL muffler.

It was going to be much too tight to cut out the inner pipe through this small window, so I decided to cut out a much larger piece of the muffler side-wall. In for penny, in for a pound. You can see the first cut I made along the weld.

busy busy
I cut along the weld line hoping that the welder would be able to put it all back together again easily. When I later talked to him, he said it wasn't necessary, but it was also ok how I did the cutting.

busy busy
Now we're talkin.

The inboard end of the inner pipe looks like it is held in place with a wire mesh gasket. I could not see any signs of welding anywhere in the area. --->

busy busy
If I could cut the inner pipe through right near the cat con material, I might be able to put the end piece out easily. I drilled holes all along the cat con material and then used the chisel to break out the metal between the holes. I also used the Dremel and Makita to cut away material where I was unable to drill holes.

Walla, it is done! --->

busy busy
Once I cut all the material away, the end piece came right out, just as planned.

I trimmed off some of the rough edges on the theory that I didn't want any small pieces to be burned off and them come through the muffler while riding.

Here's the end piece (left) and the WR250R cat con (right). --->

Here's a look into the middle section of the muffler - a hollow chamber with two exit pipes leading to the rear section.

I did make an error while cutting out the large window - I should have cut about 2 inches further inboard on the front end and I would have missed cutting into the inner pipe. I'm hoping this will not be a problem for the welder. Later, he told me it wasn't a problem.

Ready to go to the welder this afternoon.

In retrospect, I should not have messed with cutting the small window out and instead cut the larger window out right from the start.

busy busy
Back from the welder - ready to paint. He did a good job welding the pieces back on.

Three light coats of Hi-Temp paint and it's ready to mount on the CRFL. --->

Back on the bike with the B&B spark arrester with turned down tip.

Muffler sound and weight numbers:

Stock   87 12.25
NoCat StockSA   87 10.125
NoCat B&BSA   92 10.25
NoCat NoSA   96   9.25
FMF   96   5.25

dbc = dbc scale on my sound meter
NoCat = muffler without catalytic converter
NoSA = no spark arrester
B&BSA = B&B spark arrester

Installing an FMF muffler

See the Exhaust changes panel on the Modifications web page.

Quieting down the FMF muffler

The first task was to remove the shell. This was easily done with the muffler mounted on the bike. I removed 4 bolts and the back half of the muffler body slid off. Then I forgot to take a picture showing the stock packing material in place. This picture shows some new packing material wrapped around the body during a test fit. As you see, it's too long and will have to be trimmed a bit.

Here's a look at the metal mesh that FMF installs. The metal mesh was spot welded at many places along the length and around the circumference; it wasn't going anywhere easily.

The bare guts. I plan to cut off the spark arrester/tip assembly and slide some smaller diameter perf pipe inside the existing pipe. Then I'll modify the spark arrester and tip, repack with the new packing material, then put it all together and hope for a quieter FMF muffler.

More to come, stay tuned...

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