Hi all,

I have been working on modifying my k100 and am getting near completion. My issue is that I took my bike for a test ride about 4 weeks ago with the standard exhaust and was impressed in the way it ran. I then took the bike to a friends house who disconnected the battery and set about making a custom Collector to allow me to fit a different muffler. The collector is around 40mm at its smallest diameter, and from this I fitted a shorty reverse cone muffler.

I picked the bike up and reconnected the battery and the bike started without fault. I took it for a ride and the bike seemed to lack power and acceleration and was disappointing to ride. Suspecting restriction being the cause I removed the Baffle from the Muffler and took for another ride with no change to performance..

Am I right in suspecting that the collector is causing restriction and therefore poor performance. Or is there a possibility that the battery being disconnected for 4 weeks has affected the Computer (doubtful) or as with some car CPU's does the computer have the ability to self teach based on bike operating feedback.

I have seen these Mufflers fitted to other K100 bikes but have not read about the issues I am having.

Thoughts?

The 40mm section should not be a restriction but I would be replacing the old muffler, you need to get something really good to be better than the standard muffler.
I know they are ugly as, but they do work well.

Thanks Rick, I agree about the standard unit. Anyone else have any thoughts

Luftmiester made a replacement that was a little throatier. 

You might find a used Remus for the K1100 or K1200 that your collector could be modified to fit.  

FWIW your K will likely never be as loud as a HD

Rather than being too restrictive I would've thought your new system is not restrictive enough, allowing more exhaust gas to escape more quickly from the combustion chamber which leads to a colder mixture inside the chamber which doesn't burn as well, and lowers the actual compression. It is also a little easier for fresh air to enter, the whole lot will upset the fuel mixture. Does it pop on overrun? Have you tried shoving something like wire wool inside and then using the baffle to hold it in place?

Anytime you change an exhaust system you have altered the engine's fuel air requirements. On carb engines you re-jet the carb until you get the performance back. On injected engines it's a little trickier in that you have to consider an injector with a higher fuel flow rate and possibly re-map newer ECU's. On your K you don't have to worry about re-mapping but a richer air / fuel mixture is needed with the extra flow your new exhaust system is developing. Your engine was designed from the fuel tank to the tip if the exhaust with exacting parameters and a very specific amount of exhaust back pressure was calibrated into the fuel / air ratio when it was designed. All too often I encounter poorly running engines that have had exhaust alterations without air/fuel and ignition timing being taken into account as well. Bottom line .... Too much exhaust flow equals a poorly running engine throughout it's torque curve unless (again) air/fuel ratio, ignition timing, cam, compression etc are taken into account.... Back pressure (and exhaust system tuning) is your friend.

keg what model ?  8 valve or 16 ?

the outlet restriction or lack of will be duplicated on the inlet with starvation if opened up further than usual  . 

many folks forget this little factor  but "classically"  torque is gained by having  slightly more restriction on exhaust  than inlet ...so makes sense to me that to get any gains you need to be able to breath air in at a higher rate than standard . to match the new outlet flow at least . 

if its an 8 valve  try removing the restrictive inlet tube  to the air - filter box which will limit the amount of airflow , once the inlet flow gains some more breathing to the afm (which maps the air flow volume in a completely analogue nature ) will be significantly opening further ...thus richening up the mixture in a direct relationship to airflow .

we have seen folks modding the airbox to open it up further after modding the flow on the exhaust, with good results ...others have left the air paths the same and implemented k1100 throttle bodies inplace of the k100  with some more but limited and subjective torque gains noted .

I guess you have to consider the rev range where this increase is expected to be applied ...don't forget we have a tuned length inlet path designed into the system with ram stacks into the plenum and a nice overlap of the cam timing (works best at revs above 3.5 k )


just what I have been reading in here over some years