Tech: Why Does My New Bike Shudder and Stall With Aftermarket Exhaust and Fuel Tuner?

2015 Kawasaki Vulcan Vaquero reacts violently to new pipes, high-flow air filter and fuel tuner.

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Reader Marc Nickens' 2015 Kawasaki Vulcan Vaquero with Freedom exhaust, Big Air filter and Dynojet PCV.

Q. Just this year, I bought a 2015 Kawasaki Vulcan Vaquero. Recently I changed the exhaust to a Freedom Performance Combat 2-into-1 exhaust and put on a Big Air kit from Thunder Mfg. and a Dynojet Power Commander V.

Since making these changes, my bike tries to stall at lower speeds. Typically, if I try to maintain 30 mph, the bike will violently shudder as if to shut off unless I throttle up or release the throttle in a hurry. It also burns way too much fuel now. I was getting about 250 miles to a full tank, but now I’m lucky to get half of that.

Since Freedom Performance provides no port for the oxygen sensor on their pipes (they actually told me to drill a hole in the pipe—seriously?) I’ve had to use an O2 blocker to compensate for this. My bike still tries to shut down, and I still get crappy gas mileage. What gives?

Marc C. "Hyde" Nickens
Verona, PA

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A. Obviously, it's running excessively rich. The first step is to double-check the physical installation; ensure that the Power Commander is installed and connected correctly. If you're comfortable working with the Power Commander's PC software, you can check things like the calibration of the throttle position sensor and look for error codes with the Power Commander itself. Next, see which map is loaded. It appears that there are no custom maps available on the Power Commander site beyond one designed for the stock exhaust and air filter, so you're a little on your own there.

Next, check to see if a map is even loaded into the module; if there are numbers in the spreadsheet-like page, then you have a map; if they’re all zeros, you have what’s called a “zero map,” which does not change fueling or ignition timing over stock. Whatever you have, it’s clearly not working, so you’re going to need a new map.

Your next resource? Fellow Vaquero owners. Check online to see if someone else has developed (or has had built) a custom map for your combination of exhaust and intake. We found quite a discussion about Power Commander tuning over at You might be able to borrow another owner’s map and give that a try.

Barring that, let the pros have a shot. Find a Dynojet tuning center and have a custom map made for your bike. Based on our research, it seems owners are happy with aftermarket intake and exhaust systems as long as they’re mated to the proper map. You might notice, too, that some owners have found a solution to exhaust popping during deceleration. Your Vaquero should run better than it does. Keep going and you’ll find a solution.