I bought a 2006 f4i at the beginning of the summer. The previous owner had done a sport seat conversion and put a Delkevic 8" slip on exhaust on it. He kept the stock exhaust and gave it to me when I purchased the bike.

When I brought the bike into the shop for an inspection after I bought it, the mechanic seemed to make a point about how he doesn't recommend aftermarket exhaust. His reasoning was that the bike was engineered to run with the stock exhaust. He then went on to say that as long as the bike is not backfiring with the Delkevic then it is fine.

With the Delkevic on, the bike sounds a bit inconsistent while idling. It also sputters (pops?) when I lay off the throttle. Is this bad? I've spent sometime researching this on these forums but not sure I found an answer.

So this weekend I decided to put on the stock exhaust to see how the bike ran on that. With the stock muffler bolted onto the rear passenger peg, it doesn't slip totally on to the exhaust. It does fit barely around the exhaust and I was able to tighten the clamp, but it could slide on another inch to be fully on.

I'm not sure which of these situations is better (as far as performance): the slip on with possible back fire or the stock with a somewhat loose connection.

 

It looks like getting a PC3 might fix the sputtering problem with the Delkevic....

 

Slip-ons, on their own, don't affect the bike very much. Issues arise because bikes tend to be set pretty lean from the factory to help pass emissions. Putting a slip-on makes them run even leaner with the less-restricted air flow. This in turn makes the engine run a little hotter.

It becomes a more noticable issue with a full exhaust system, or a high-flow air filter + slip on which leans the bike out even more. At that point it's recommended that you get a Power Commander to adjust the air/fuel mixture correctly.

FWIW, I put my stock exhaust back on when I bought my bike because it had both a slip-on and an air filter but no Power Commander.

 

Thanks for the reply. I have my stock exhaust on right now, but I have a K7N air filter and a PC3 in the mail. I think I'll put my slip on back on when these come. The only thing is the Delkevic 8" can is so damn loud! I might try to sell the stock and the slip on and put that moneys toward another slip on that I can handle.

Also, does your stock slip fully on on the exhaust connection? When it's on, does it have any play for movement? Mine can rock side to side but will not move back and forth (due to the connection to the pylon).

 

I didn't notice. It was tight enough so that I didn't think about it.

 

Aftermarket exhausts come with a mid pipe also, the pipe in between the headers and the muffler. If you only removed the Delkevic muffler and are trying to put the stock muffler onto the aftermarket midpipe, that could be your fitment issue.

I've actually never dealt with a stock exhaust so I can't say much beyond that. Mine had aftermarket when I bought it and it's been all aftermarket since.

 

The stock exhaust should be one piece to the end of the headers. They must have cut it at one point. On mine (2002) the pipe is stock and all welds to the headers, and at that point is the clamp. Anyhow if you are using a pipe that was clamped before it usually will be very tight due to clamping the first time it was installed. They make a tool to ream (widen) the pipe a little to make it easier to install again. Harbor freight has one but I never used it, or saw it so I dont know if it is any good. Possibly auto zone has the tool to do this, they loan tools out, that would solve your problem, otherwise a block of wood and a little tapping w/ a hammer should get it back on? Good luck.

 

My '01 wasn't cut, and it's definitely two pieces; slip on, then midpipe+headers.