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​ Do You Need To Re-Jet Or Add A Fuel Processor When Installing Aftermarket Exhaust?

​ Do You Need To Re-Jet Or Add A Fuel Processor When Installing Aftermarket Exhaust?

Posted by West End Motorsports on Apr 28, 2017

Black and white photo of a motorcycle

The number one question we get here at West End Motorsports is, “Do I need to rejet or add a fuel processor if I change my exhaust?”

In cases where the motorcycle is running properly, you do not have to make any adjustments 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 recommend re-jetting or adding a Fuel Processor to enrichen the air/fuel mixure when changing to any aftermarket exhaust. If you are changing the whole exhaust system that greatly reduces back-pressure and/or adding a high flow air filter (see below), the fuel/air mixture will need to be addressed by adding a fuel processor or a jet kit to keep your engine from running to lean.

West End Motorsports Recommends:

1. If you think your bike has a lean or rich condition already: Re-jet if carbureted, Install a Fuel Processor if you have Fuel Injection.

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 add a Fuel Processor. 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.

Harley Davidson Touring air filter kit

Arlen Ness Big Sucker Stage 1 Air Filter Kits for Harley Davidson Touring Models '17-Up - Black Backing Plate

Do I need to re-jet 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 add a Fuel Processor to 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.

Vance & Hines FuelPak FP3 connection instructions

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 V,Vance & Hines FP3 FuelPak or a Cobra FI2000R PowrPro Black 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.