Fuel for Thought, A Beginner's Ineptitude, the Hokey Pokey and a Stumbling Ninja | Answers


By Tim Carrithers, Photography by Vp Racing Fuels

Got A Question For Answers? Send It To mcmail@sorc.com

Fuel for Thought

I’ve heard guys talk about running aviation fuel or race gas in their streetbikes for track days. They say it adds power and is better for the engine while it’s running at high rpm. Is there any truth to this? I’ve always thought race gas was only suitable for highly tuned race engines.
Andrew Langford
South Bend, IN

As with most seemingly simple queries, the answer to this one is more complicated than you’d think. According to Bruce Hendel at VP Racing Fuels, avgas is for airplanes—period. “The main difference is an aviation engine is designed to run at 3000 rpm, while most sportbike engines perform from 6000 to 14,000 rpm,” Hendel explains. “Using aviation fuel in a bike that can run on pump gas will actually make less power.”

Most streetbikes don’t need a higher-octane fuel to prevent pre-ignition. Bigger octane numbers don’t necessarily deliver better performance. “Most people don’t understand how octane numbers are established. An octane test machine only runs at either 600 or 900 rpm, and octane is only one factor. Today’s fuels make power through more oxygen and higher quality components that deliver more energy than pump gas. We suggest a couple of fuels for track days: MS109 unleaded is for bikes with catalytic converters. Leaded U4.4 makes slightly more power in those without a cat or oxygen sensor. There’s also MR12, which is a Pro-level fuel that makes more power in stock or modified engines—up to 10 percent more than pump gas. But since its octane rating is lower, the other two are better in more heavily modified engines.” Hendel emphasizes that these three fuels are strictly for the racetrack and recommends VP100 unleaded for maximizing street performance. It contains ethanol like pump gas and remains stable longer than garden-variety unleaded, but it’s not cheap. Expect to pay $7.75 to $9.50 per gallon for VP’s street-legal stuff depending on where you live, and still more for the real-deal race gas.

Enduring Ineptitude

I’m afraid I’m one of those people who, as Keith Code puts it, are “completely inept and probably should never have ridden a motorcycle.” I’m a Motorcycle Safety Foundation Basic RiderCourse graduate who’s logged barely 800 miles, and I’ve already crashed three times because I still lack basic skills. At this rate, I’m going to be roadkill a lot sooner than later. How can I become a competent rider without learning everything the hard way?
Michael Liu
Moorpark, CA

It’s certainly possible that you might be one of the completely inept. Motorcycles aren’t for everyone, and three crashes in 800 miles has to be painful in more ways than one. If you’re still determined to give it a go, you might try the MSF’s two-part Street RiderCourse outlined in this month’s Street Savvy (see page 92) Street Street. A little interaction with the instructors there should give you a much more realistic idea of whether motorcycles are for you or not. The other option is to get a dirtbike, so your crashes will occur on a softer surface without any four-wheeled vehicles around to run you over.

Do the Hokey Pokey

How come Casey Stoner and some of the other MotoGP racers hang their inside foot off the bike as they set up for a corner? What are they doing?

A certain Valentino Rossi gets credit for perfecting the technique, which he says helps him brake harder and deeper with more confidence. Hanging that inside leg off the peg is a relatively easy way to shift body weight quickly and precisely down toward the inside of the corner where it does the most good under heavy braking.

Stumbling Ninja

I read your road test on my 2002 Kawasaki ZX-9R. It stated that there’s a low-rpm stumble, and that there’s an easy fix, but it didn’t say what the fix is. I have that same problem with mine. Do you know what fix we’re talking about?
Steve Squilla
Rochester, NY

The 40mm Keihin CVKD semi-flat-slide carburetors on your ’02 ZX-9R left the factory with appallingly lean jetting. Opening the mixture-adjustment screws and jettisoning the undersized stock pilot air jets will help, but those tweaks evade the main problem while creating new ones. The real cure is an aftermarket jet kit, and the best one comes from Ivan’s Performance Products (part number 9R-9802; $140 from www.ivansperformanceproducts.com). Exhaling through a slip-on muffler on the standard Kawasaki header, it irons out all those annoying wrinkles in the Ninja’s power delivery from idle on up. One of Ivan’s ignition advancers helps as well, though it also makes the idle rpm a bit unstable. Start with the jet kit and take it from there.

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