Join Date: Jul 2018
Location: I split my time between rural central Iowa and rural southwest Iowa
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If you change from the stock muffler to a slip on exhaust, you don't have to tune. If you change the whole exhaust to a 2 into 2 or straight pipes, you need to tune as that will dramatically change the back pressure.
If you change the intake, the engine is now able to suck in considerably more air than before, thus really leaning out the fuel/air mixture. You have to tune so that the fuel injection system knows to add more fuel. Running lean can cause performance problems. Running lean of peak also causes the engine to run hotter and can burn valves and even pistons.
In the old days you would change the jets in the carburetor. Now you need to tune the electronic ignition. Several ignition tuners are on the market including the Vance & Hines Fuel Pack 3 and the H-D Screaming Eagle tuner. Go to a site like jpcycles.com, revzilla.com, or bikebandit.com and search for your bike and then under fuel system type stuff. The exact keywords vary by site.
The FP3 seems to be the most popular in part because it's the least expensive and also because it has an easy to use phone app. You install it, pick the parts you have on your bike, flash the ECM and away you go. If your exact exhaust and intake don't show up, call V&H and they will suggest a map. The FP3 also has an autotune function that has you ride the bike for a couple of hours and suggests a revised map for you to flash the bike with. That's really handy if you don't have an exact parts match for the initial map.
If your bike is from model year 2017 or later and still under warranty you have another consideration. The EPA busted H-D's chops regarding tuners, so if you use anything other than the H-D Screaming Eagle tuner on your bike and H-D finds out about it they void your warranty. If you are out of warranty or are riding a new old stock bike that isn't a concern.
Most of the tuners can be disconnected except while you are flashing the bike or running an autotune session. Some, like the FP3, can be used to emulate some instrumentation that H-D left off the bike from the factory.
Formerly known as "PugslyCat" until the account got locked.
2016 xg750 in Velocity Red
2007 Sportster 1200 Custom in blue and silver