F650 Classic Cat Converter FAQ
compiled & edited by Kristian #562
Please read the Disclaimer
before attempting any work in this FAQ.
Last Updated: 14 June 2007, by Winter #1935
Other related FAQs:
This FAQ is about how to remove the catalitic converter from a Classic
F650. If you have a GS/Dakar please see the GS Exhaust Modifications FAQ.
Pardon my ignorance, but why remove the cat?
Unleaded gas isn't available in some parts of the world. Leaded
gas will ruin the catalytic converter. And a cat gets ruined by melting
and effectively restricting the exhaust to where the motor will no longer
run. THAT will ruin your day.
Method 1 - Cutting open the SIDE of the Exhaust
by Mike #410
You should be able to tell where the hole was cut by looking at the
pictures (at the end).
- Make sure it is INSIDE the factory welds.
- The big round can is the "cat" and you ain't gonna beat that
sucker outta there cause its in a heavy metal tube.
- Cut it out with a torch till the end of the pipe is wide open.
- Before welding the piece back in place be sure to remove
the perforated chuck of metal on the back (inside) of that piece.
Otherwise its liable to come loose and rattle.
- The plasma cutter is the way to go when cutting
the hole. Nice narrow cut with no warpage to deal with. I used a mig to
weld the piece back in and touch it up once in awhile with some paint to
keep it from rusting (if it worries ya that is).
- Motor runs a LOT cooler without the cat. Fan don't kick on near as
often and your left cheek don't get fried in traffic.
- Plus you can run leaded fuel if you want or need to. I went
ahead and cut and plugged the tube from the exhaust to the airbox and
turned out the airscrews a bit and it cured ALL the popping on
- My local welding shop charged me 25 bucks to cut the hole, melt
out the cat and weld it all back together again.. A lot cheaper than a new
pipe. And when you're done it is no louder than stock.
Method 2 - Cutting open the SIDE of the Exhaust
I did it and the way its shown (above) is not the best way. Cut out a
triangle forward of where its shown in the pictures. Then cut the can/cat
out that will be much easier for your welder. If you do it the other way
you will agree with me after it is done. Here is what you should do:
- The yellow line is where you should cut you
could make the hole bigger by going further towards the front of the can.
- I tried to show that with the yellow dotted
line. When you make that cut you will see that the pipe that enters the
cannister continues into the cat part of the exhaust. The blue lines try to
- If you try to cut at the red arrow you will
have fits cutting through the material that the cat is made of that is very
difficult and unnecessary.
- The orange lines show where you should cut.
One line goes straight through the pipe as it enters the cat area. It will be
before the cat material and easy to cut through.
- The other orange line needs to cut through the
panel that holds the cat in place. So that orange line needs to be rotated
onto the panel (shown by the welds) that is 90 degrees from the direction of
the picture. By doing it this way you will get more weight out of the
cannister and save a lot of time cutting.
- The blur line with orange around it shows the
panel that holds the cat along with the orange arrows.
Q. After learning this morning that my Rotax muffler
does not work with the Jesse mounts, I took the OEM muffler down to the local
Mexican welding shop to have the Cat removed. I need to be able to use Leaded
gas if no other option is available. They cut, removed, and welded, but they did
NOT find a white honeycomb piece of ceramic as I have heard Catalytic Converters
look like. Instead, they found and removed a whole bunch of stuff that looked
like steel wool. WAS THAT THE CAT? Or did we merely remove the "muffling" agent
in the muffler. I went back today and had my friends "touch up" the muffler a
little and remove the real CAT. Didn't realize an ILLEGAL procedure such as this
would be on the FAQ, but there it was when I got home last night, so I took that
info back to the welder. With all the cuts and welds and crap all over the
inside of the muffler now, it looks more like I mutilated the cat, than killed
it. But with all the muffle gone, it sure sounds throaty for a Beemer...
A. You will always find a cat as close to the engine exhaust
port as it can be placed in order to keep it nice and toasty, so look for
the first bulge that you see in the exhaust system snake. It is likely to
be hiding there. The steel wool is likely the muffling material. Richard
- I killed my cat per the FAQs. It definitely runs cooler, but it's
still hotter than I like it. Now I know why BMW riders wear high
boots---too much heat on the right leg. I haven't been able to get my
carbs adjusted correctly though since the cat event and I am at 6300 feet
in altitude, which I think causes some extra challenges. Colorado Bob
- So Happy and the F
Runs Great! In 2001 I took a trip to Alaska on the F 650 and on the way
stopped in Redmond OR for the MOA Rally ... WOW!! and then onward and Up to
Alaska .... Double WOW!!! But on coming back it was apparent that the roads
and travel (od was 26K miles) had taken a toll on the F so with recent
marriage and things the F stood in the garage for a season waiting and then
this spring I tore into the bike and fixed and improved much! So the last 3-4
weeks I redid the carb with Dyno-jet and replaced all the insides, then the
airbox with a air-enricher ectomy and snorkel-ectomy and organ pipes .....
then air filter is the same so...... the exhaust is stock but the Cat was
taken out by my friend with a arch welder. Then the weakest thing ..... was
replaced .... the stock shock now it is a Ohlins. but also all the bearings in
the swing arm and arms .... all replaced with caged bearings ... Torrington's
and repacked :))) The cooling pump was old and weeped so a new cooling pump
with seals . then all put all back together ........ Many Hours and today all
done!!!!!!!!!! I took it out today and the carb and exhaust mods make the bike
FLY! WOW! So many things I missed in the details but the FAQ's and the people
that help each other in the Chain Gang make the F 650 the BEST ! Thank
You! Happy Easter! Charlie C '97 F650 Travel and Adventure, OooRaaaaa!
- The carb/exhaust
Mods : Well 1. Dyno Jet Kit with Needle to 2nd stop and 134 main jet and I
used the Dyno spring. 2. idle screw at 3.5 turns 3. the stock muffler with Cat
taken out and air enricher taken off. 4. float level ...14.6 mm. So far to
hard to tell.... I need much more time to check mpg and richness or leanness.
But the pick-up (more so at higher end...somewhat at low) is Much Improved :)
Yes I am so surprised about the ease and improvement of the F650 with refit
concerning the Dyno-jet kit and stock deCat muffler (okay the scoop; Dyno
needle @ 2nd stop, 134 main, float at 14.6mm, rebuild and cleaning of the
carbs inside, Dyno springs, idle mix screw @ 3.5 turns) and WOW!! the
improvement is modest and consistent ...not to rich and not lean:)))) The MPG
with wife and me in a strong head wind with a best est. was 40-45 mph ... hard
to tell with only 51 miles traveled. But going after all the little problems
with a wrench and F650 FAQs have given the F a new state of tune that is so
much better than pre-Alaska and really much better than new..... well BMW
sucks at making a product that is 100% ready for the market place with all the
bugs out (the quality and character is the best !!!!!) but this bike is @#$%#
Great !!!!!!! (factory stuff taken off: Canister, Cat, factory tank, air
box/exhaust air enricher...LOL!!!) I proclaim never let BMW wrench on your
bike ..... NEVER because they screw something or fail on fixing something
....all the time and the cost ..... WOOOO! Yes the time I put into rebuilding
and customing the bike with electric heated seat, Acerbis tank, engine guard
with highway pegs ....... and now with Dyno-carbs and deCat exhaust ..... much
time But all THE BETTER..... 'Zen and the art of motorcycle Maintenance' :)
OOOORRRAAAAAAAAA!!!!!!! I have reached 'Zen' :))))))) Thank You:)))) Charlie C
'97 F650, Travel and Adventure, OooRaaaaa!