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stock can / slip on

I have experienced this a few times. When I sold my DRZ, I removed the Yoshimura full exhaust and put on the stock unit. I'm sure it was still jetted for the exhaust but I found that the bike ran much more smoothly with the stock bits. My SV650 had a Yoshimura slip-on and I installed a silencer tip on it and found it felt better that way as well.

Who really knows if it's real or just our senses looking for things to confirm what we want to believe.
 
No surprise there. Most mods done on engines don't really make it run better overall, it might help in one area but often there is a tradeoff as some other aspect is affected to a negative extent. The manufacturers have to make sure their equipment runs as smoothly as possible while meeting all the safety and EPA regs and they have access to the best engineers and design/test equipment to make this happen. But an aftermarket can is just an approximation for any particular application, hence they often run poorer. Most are sold to make them louder because people believe louder means faster and more power. It is often a knee jerk reaction to automatically replace the stock muffler to improve the performance, it often doesn't.
 
I replaced the stock can on my SV650S because I heard another SV with the same can, and liked the way it sounded. I didn't realize until the installation, how much heavier the stock can was. So, there was the weight savings and it sounded cool ... But at the end of the day it's not a race bike, and it's actually probably too loud now ...

So who knows, to can or not to can ...

I will tell you this though, I don't plan on swapping out the stock cans on either my FZ1 or my 1190 ADV, anytime soon. They are performing well as they are.
 
The stock fuel mixture is programmed on the lean side, in order to meet emissions requirements. In fact it is just on the verge of, but not quite so lean that the bike would surge or run so lean that it would be noticeable in normal riding.

The slip-on creates less back pressure. This means that the cylinders are more thoroughly scavenged. So instead of re-burning some of the mixture left over from the previous ignition, a greater portion of the mixture is freshly induced from the intake. The net effect is that it leans the mixture in the combustion chamber even more. Now the mixture has become so lean that it may misfire, surge, or simply lack power to the point of being noticeable.

If the mixture was programmed richer, the slip-on will produce more power. But to do this correctly, it may need more fuel at certain RPM and % throttle openings, and not in others. This makes the process quite involved, with the use of a dynomometer, etc.

I had developed an economy fuel program on my PC V, and a performance program. Upon switching the exhaust from stock, the bike would no longer run well with the economy program. I had surpassed the limit of lean mixture, and the bike ran poorly. I switched to the performance program and it runs great. You have to be gentle with the throttle, or the MPG will take a nosedive.
 
without tuning to compensate for the changes, no mod is worth a penny for performance. so, you are correct, it runs better stock than it does with the slip on, which actually will make it perform worse than stock without tuning to accommodate the change.
 
Yeah, I should've said in my reply above that I had to add a Power Commander along with the slip-on - to deal with the aforementioned fueling issues.

Edit: So there's that to consider when pricing an exhaust as well, the added expense of the PC and any needed tuning/dyno time - if it won't run well on one of the generic PC fuel maps.
 
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Good arguments for the stock can. Here's another, I had Vcyclenut flash my ECU but told him I want to keep the stock exhaust. So he kept the stock fueling but removed the restrictions from the first three gears and removed the fuel cutoff. We kept the AIS operating and lowered the fan actuation temp.

The result is a bike that runs like it should, is very quiet and gets 42 to 47 mpg on the highway at 75 mph. I'm very happy with this set up and spent the money I saved on tires and suspension plus a few other convenience doodads.

Also about the weight argument, I'm not too concerned that the stock can weighs about the 5 to 8 pounds more than a slip on than I am about the extra 20 pounds on top of the bike (I need to diet).
 
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