I apologize for bringing up a KLR question on the KLX forum, but I think the expertise is more expert over here. And, I think this question would apply to a KLX as well.

I just picked up a KLR650 which came with a Supertrapp aftermarket slip-on muffler. So far I like the bike for highway/back road riding, which is why I bought it. But, I hate the loud pipe. This particular muffler, supposedly, can be tuned to make it quieter, but apparently, not quiet enough.

I suspect the original factory muffler would be quiet enough, but don't want to part with the cash or add the extra weight.

I've started tinkering with the Supertrapp, mostly reducing the size of the outlet opening. The Supertrapp has a 2-inch rear opening, but may not have a big effect on the muffler's loudness or resistance, due to the unique design of this muffler. I have tried inserting a pea shooter 1-inch diameter pipe with great success noise-wise.

I suspect a 1 1/8" or 1 1/4" may work as well, resulting in quietness similar to the factory muffler. A brief test run did not show any lack of power at high speed.

My concern is whether I might damage the motor in some way by over restricting the exhaust. I think it will make the motor run richer, but will that result in damage?

Any guidance would be greatly appreciated

 

You will probably be OK but there's always a risk when you experiment. Personally I would buy a used stock exhaust which could be had for cheap and sell the Supertrapp for some good cash. You won't really notice the exhaust weight because the bike is already a top heavy bike and adding a few extra pound will be barely noticeable. Either set up, you should verify the jet sizes. Pull the spark plug and read to determine if your jetted is OK or pull the carb and dismantle.

 

I personally wouldn't see any ill effects as long as you didn't restrict it any further than a stock sized outlet. But you may effect your jetting!


On a side note, I had a supertrapp on a 1999 Polaris Scrambler 500 for about 3 rides. It was so freaking loud. The guys I rode with even complained it was so loud. They always made me ride in the back. I went to a quieter exhaust.

 

I bet if you got on ADVRider or an active KLR forum, you'd find someone who'd trade straight across for your supertrapp. That's the route I'd go.

 

I have a Supertrapp on my KLX650. You talk about an exhaust opeing, the tuning is done by the number of discs, which is also the control over the sound. I have 12 discs in mine. It is a bit loud when on the bike, but oddly enough, no one has told me it is too loud. I've asked for opinions and heard others ride it. Seems okay as it is.

This is what it looks like, although mine is built into the end of the Baja Designs pipe I have.



No open end, the end cap is a relatively heavy cast aluminum part. There is also a stainles domed cap on some, doing the same.

If yours does not have those discs and cap that is your issue.

Here are the three main styles of caps, the open competition one would be way too loud for me.



I plan to go with six discs on my Pro Circuit pipe (near identical to the BajaDesigns) for my 250. I figure if 12 works on the 650 six should be fine on the 250.

Whatever you do, use some anti-seize on the allen bolts, they are stainless and can gall in the cap, seizing in place. You could do 8 discs to start.

 

Mine is the IDS2. The discs are recessed about 4 inches in from the rear of the muffler body. Then there's a cast aluminum cap on the rear with a large 2" diameter opening.

The muffler came with 12 disc inside and I have reduced that number to 8, then 6. I'm sure it has a decent sound if you like loud exhaust. I do not.

I've played around with reducing the rear outlet and has made a dramatic difference. It sounds more like a whoosh vs a bam, bam, bam. If I can be confident that no harm is done to the motor, I will proceed with making a permanent attachment to the rear of the pipe.

I also check the plug tonight and it indicated a slightly lean condition, so I may have some room to play with exhaust-wise.

As you've said, people hearing from a distance say it's not too loud, but from the riders seat it's shear agony to me.

SuperTrapp: Performance Exhaust

 

maybe see what the stock exhaust outlet size is

my 300 had a pinky size outlet
a 125 had a finger size outlet

so it all varies from different bikes


ive experimented before with making aftermarket exhausts quieter
main difference ive heard is you loose all the bass when doing so. which of course makes the most noise

 

I just wondered when you talked about the opening. A lot of Supertrapps end up with all the discs and stuff gone, leaving a wide open straight thru silencer that doesn't do much.

I'd think you could close down to the size of the header if you wanted.

Other option which shouldn't be horribly expensive - get a used stock muffler.

 

On my KLX250S, I have an FMF PowerCore 4 muffler. I found it too loud. I took some sheet metal and bent it to make a 'cone' shape and used the existing threaded bolt hole and put the cone in the end of the muffler taking it from probably a 1.5" opening to about a 3/4" opening. It made a dramatic difference in loudness, but no appreciable loss in power. The stock muffler (which I still have) is WAY down on power compared to the FMF, even with the home-made silencer installed. So, that might be an option for you?