Unfortunately, there is no definite answer to this question. In some cases where the motorcycle is running properly, you do not have to make any sort of adjustment when changing the exhaust. This is especially true when adding slip-on mufflers. The short mechanical reason for this is that changing the exhaust does not directly add (or remove) air or fuel to your engine. So there is no reason to adjust your air/fuel ratio to compensate for the change (which is what rejetting/remapping does!). That being said, many motorcycles come from the factory with a lean air/fuel mixture and do benefit from an adjustment. All aftermarket exhaust manufacturers do recommend rejetting/remapping.
West End Motorsports Recommends:
1. If you think your bike has a lean or rich condition already- Remap/Rejet
2. If you feel your bike is running correctly- It will not hurt your motorcycle to put on the exhaust and give it a test run. If you install the exhaust and experience poor throttle response, backfiring, popping on deceleration or excessive heat, then go ahead and rejet or remap. If you install the exhaust system and are satisfied with the results- Great…keep riding! West End Motorsports will not tell you to buy or not to buy an aftermarket fuel system. We simply present the facts as honestly as possible (we have no reason to lie to you- We sell the entire line of aftermarket jet kits and fuel processors!), but the decision is yours. Ultimately, making an adjustment can optimize performance but is often not necessary.
Do I need to rejet or remap my fuel system if I change my air intake?
Absolutely! When you change your intake (adding a free flowing intake or filter) you will need to remap your fuel injection or re-jet your carburetor. The short mechanical reason for this is that changing the intake directly adds to the amount of air going to your engine – so you must adjust your air/fuel ratio (add fuel) to balance the change.
For carburetor models: Most air kits state they come with jetting but they only include larger main jets. We recommend buying a Dynojet jet kit separately to take advantage of the Dynojet needle which has a finer taper and will give you better throttle response.
If your motorcycle is fuel injected you will need to remap your fuel system. This can be accomplished with any aftermarket fuel processor such as a Dynojet Power Commander or a Cobra FI2000 Tripot Fuel Processor. Look in the Engine/Performance category for your model for pricing. There should be several different brands available for your particular application.
In either case since you are adding significantly more air to your air/fuel mixture with these kits, adding more fuel is required. Not rejetting or remapping your air/fuel mixture could result in excessive heat buildup, causing significant damage to your motorcycle.