Motorcycle Backfiring and Tire Wear


By Tim Carrithers, Photography by Kevin Wing, Yoshimura R&D

Q I replaced the stock exhaust and EXUP valve on my 2007 Yamaha FZ1 with a Yoshimura slip-on, and replaced the stock air filter with a K&N. The problem I have now is when decelerating, I experience loud popping, crackling noises coming from the exhaust. I then purchased a Cobra fi2000 fuel-injection box, which improved throttle response but did nothing to help the backfiring. What can I do?
Troy Resch
Buena Park, CA

A According to David Tsai, resident product expert at Yoshimura R&D, the popping you hear is symptomatic of a lean condition brought on by either air leaking into the exhaust system or the net effect of your changes. His first suggestion is to check the junction between the stock header and the slip-on. Accumulated crud there can cause a leak, even if the clamp is tightened down correctly. "It helps to clean the connection with an abrasive cloth," Tsai says, "just to make sure that connection is sealed tight." It couldn't hurt to go over the area with brake/contact cleaner, and apply a thing coat of copper paste or high-temperature lube. If that doesn't help, move upstream.

"The Cobra Fi2000 is a piggyback fuel controller, which works by modifying low-, mid-, and high-speed EFI signals based on throttle position, or 'load,'" Tsai continues. "If you're getting popping noises when letting off, try increasing the low-speed adjustment by two clicks, increasing the fuel in low-throttle positions. It would also help to increase the mid- and high-speed by one click. Those modifications (air filter, exhaust and removal of the EXUP valve) increase airflow significantly, and fuel must be increased accordingly. Additionally, the EXUP valve opens at 5500-6000 rpm and significantly limits exhaust flow in the lower rev range. This is the reason for increasing fuel in the low-speed load range more than the mid- and high-speed. Making adjustments one click at a time allows incremental changes, which can be easily reversed if results are counterproductive. Once a good setting is found, record the information. If further changes are needed later, you can always come back to that."

Highly Irregular
After suffering a flat on my 2007 Hyosung GV650 cruiser's original Bridgestone Battlax rear tire at about 5500 miles, I noted uneven wear. It was wearing more on the left side then the right. I asked one of the mechanics at my local Hyosung dealership about this, and another at a shop that strictly does motorcycle tire mounting/balancing, and neither could tell me why this unusual wear occurred. I don't want to pay for a new tire just to have the same problem recur.
Jeffrey Budeshefsky
Corpus Christi, TX

While it's hard to come up with a precise diagnosis of your symptoms, Bridgestone says it would take some fairly aggressive riding to wear out a BT054 in just 5500 miles. A more conservative approach should yield 8000-10,000 miles. Beyond that, some motorcycles do in fact wear one side of the tire faster than the other. Many riders are more comfortable turning in one direction than the other. Are you an ex-dirt-tracker? Also, any sort of misalignment can produce an irregular wear pattern. It's conceivable that some sort of construction anomaly is responsible, but not likely. Crowned pavement and/or a preponderance of left-hand bends on the roads you ride are most likely contributing to the situation.

Maybe Next Year
I just got off the phone with my local Suzuki shop inquiring about buying a 2010 GSX-R1000, or possibly a leftover '09 model at a discount. The salesman informed me that Suzuki would not be producing a 2010 GSX-R1000, but he had '09s at full MSRP and then some. Is this just a sales tactic? Why would Suzuki not build its most profitable model for a full year? I know the economy is bad, but surely they don't have that many unsold '09s to stop production!
Jon Kruse
Troy, AL

Your friendly neighborhood Suzuki dealer is at least half right. Good news first: The world economy isn't bad enough to halt production. The home office in Japan will be building 2010 GSX-R1000s for the rest of the world, but U.S. Suzuki has no plans to import any at this time. Blame our country's lingering economic malaise. Word is there are more than enough '09 models to satisfy current demand at the dealer level. The good news is it's a buyer's market. If your local shop wants full-pop for an '09, shop around.

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