Service
Service
FORKS -> FUEL -> FEEDBACK LOOP -> REVS -> ASK KEVIN
PAUL DEAN
Inverted forks are common on today's sportbikes, such as this Sachs unit on a BMW S1000RR. You do, however, pay for the added technical sophistication.
TURNING THE WORLD UPSIDE DOWN
Q: A decade or so back, "upside-down" or "inverted" forks were heralded as the greatest thing to come along for motorcycles since the discovery of fire. Since that time, a large number of bikes have adopted that kind of fork, but I still see quite a few large, expensive motorcycles that use the conventional style, bikes like the Yamaha FJR1300, Moto Guzzi Norge and lots of big, heavy cruisers. Why is this? Indeed, if inverted forks are better, why are they not universal?
KENHARRELL SALT LAKE CITY, UTAH
Ab The reasons are need and cost. When inverted forks first appeared, they were so much more resistant to twisting and side-to-side flexing that they represented a true breakthrough in front suspension design. Almost overnight, they became a must-have for serious offroad bikes and repli-racer sportbikes. But the lessons learned from that technology helped suspension engineers design improved conventional forks that, while not necessarily quite as rigid as the inverted style, were far better in that regard than ever before. That has allowed them to be fitted on some big, powerful streetbikes without compromising those machines' ability to serve their intended roles.
They also are less expensive to manufacture. A conventional fork leg consists of a steel stanchion tube and a cast aluminum slider (as well as the damping and springing internals), whereas the upside-down species requires an equally expensive steel tube, a more-costly machined-aluminum stanchion and a separate cast-aluminum lower housing that serves as an anchor point for the axle and brake caliper. If cost is a critical factor and competition-quality handling is not, manufacturers will often choose a conventional fork.
WHAT KIND OF FUEL AM I?
Q. I have a 2000 Kawasaki W650 with 1600 miles that I've owned for about 2V2 years. The bike ran fine and everything seemed normal until I had the misfortune of running out of fuel. After getting some gas, the bike has been extremely difficult to start and won't run "right." The idle rpm is erratic and can be changed just by blipping the throttle; it even will increase by more than 500 rpm on its own. And blipping the throttle at idle can sometimes produce a small amount of black smoke out of the right exhaust like it is a little rich. The whole bike is stock and appears never to have been modified. The fuel tank is clean and rust-free, and I use Sta-Bil during storage. The problem can be intermittent, but most of the time it is not right. Any help or ideas would be greatly appreciated.
GOT A MECHANICAL OR TECHNICAL PROBLEM with your beloved ride? Perhaps we can help. Contact us at cwservice@cydeworld.com with your questions. We cannot guarantee a reply to every inquiry.
KERMIT FATTIO ST. JOSEPH, MISSOURI
A with The evidence the gasoline implies you a bought problem after you ran out; prior to that, the engine ran fine. Pump gas contaminated with water is an infrequent occurrence, but it does happen, and it could cause the symptoms you describe. Some riders also have reported similar problems with gas that contains ethanol. I believe that Missouri mandates 10-percent ethanol content in gasoline; but because ethanol is less expensive than gas, there have been instances of some stations around the country deliberately and illegally blending higher percentages to increase profitability. Thus, you might have unknowingly gotten gas with higher ethanol content, and your Wóso's engine is not tuned to run properly with such fuel. What's more, although you claim the gas tank is clean, running a tank dry often allows just enough fine, undetected sediment from the very bottom of the tank to reach the float bowls and cause fueling problems.
You need to fully drain, inspect and clean the entire fuel system tank, float bowls, fuel lines, in-tank filter screen and even the pilot jets then refill the tank with gas from a station other than the one you visited after running out. I believe that procedure will cure the spasmodic running your Kawasaki is now experiencing.
THE CONVERSATION CONTINUES
FEEDBACK Loop
Add these to your list
QHey, guys, add these to your June list of
10 Things the Manufacturers Should Do:
1. Single-sided swingarms that enable simplified rear tire changes.
2. Centerstands on all models to make it easier to work on the bike and change tires.
3. Hydraulic lifters good to at least 10,000 rpm so we don't ever have to adjust the valves.
4. Low seat height (about 28 inches).
5. At least 5 to 6 in. of wheel travel front and rear.
6. Maximum weight of 500 pounds.
These would make for a perfect streetbike. Could the manufacturers build it? Of course. But will they?
TOM MOODY BROOKINGS, 0RE00N
A Thank you, Tom, for your proposed
additions; they are excellent suggestions. Some of them, however-such as single-sided swingarms and longer-than-usual streetbike wheel travel-have already been in production for quite a while on numerous models,
adventure bikes in particular. Others, including a 28-in. seat height and hydraulically adjusted valves, also are common but suitable only
for certain types of bikes. Nevertheless, we appreciate your input.
In addition to including my 10 Things list in June's Service, we also posted it on our website, and you are among hundreds of enthusiasts who have responded, electronically and otherwise, with suggestions of their own. These include a power outlet and a gas gauge on every bike, better owner's manuals, more on-bike storage for bikes without saddlebags, and conveniently placed thumbwheels on shock damping adjusters. We invite everyone to read all these suggestions on Cycle World's website and contribute their own ideas.
ASK KEVIN
When refilling the crankcase for an oil
change, it would be nice to achieve the perfect level exactly at the full mark. If it is a little low, it's no big deal; you just have less of a buffer if the level goes down over time. But overfilling seems to be a different story. The owner's manual for every bike
I have owned has had the words: "Do Not Overfill." Unfortunately, they have never explained why. What's the truth behind Do Not Overfill? What harm does too high of a level cause? I s a "little bit" over the full mark bad?
OREO MAY
UNION, KENTUCKY
A Motorcycles are capable of accelerating
and braking very hard-slightly over 1 g either way. This means that the oil surface in the engine's oil sump tips forward a bit more than 45 degrees during hard braking and tips back a like amount during maximum lowergear acceleration. The oil sump is baffled in such a way that this oil movement cannot a) slosh oil onto the crankshaft above, a condition that would generate great heat and drag; or b) allow the oil pump's pickup tube to suck air, even for an instant. But there are limits; an overfilled oil level may be too much forthis baffling, allowing oil to reach the crank.
If sump oil splashes onto the spinning crank, it turns the crankshaft and crankcase into a high-horsepower oil pump with no outlet. Scores of horsepower go into accelerating the oil to approximately 200 feet/second, yet the oil can't get away; it is swept around the case by the whirling crank. The late Dick O'Brien, longtime Harley race chief, once told me, "You could see the power loss when one of our KR engines would wet-sump on the Daytona straightaway. It was like a giant hand had just slowed the thing down." When oil got between the crank and its close-fitting crankcase, it was batted between crank and case, creating huge viscous loss-and each horsepower lost became 746 watts of heat. A loss of, say, 20 percent of engine power (0.2 x 60 hp = 12 hp) was thus the same as having 12 kitchen toasters going full blast inside the crankcase. Kevin Cameron
APB FOR THE MISSING REVS
Qb I I bought have a 2001 new. Suzuki It now GSX-R750 has 70,000 miles on it and has developed a problem in that it will not rev past about 11,500 rpm. It then sounds like it is hitting the rev limiter, which is actually set for 14,000. I'm a mechanic by trade and have always fixed my bikes but can't seem to figure this out. I have swapped out some parts from a friend's bike with no change. I've checked the valve clearances, cleaned the K&N air filter, replaced the plugs and even tried a different gauge cluster, ECU and complete gas tank. It doesn't throw any codes, and it doesn't matter if it's on the kickstand in neutral or running down the road in any gear. Please help.
LES BLOCKER ABERDEEN, SOUTH DAKOTA
A You're assume a you mechanic, understand so I that troubleshooting engine problems on fuel-injected bikes is tricky enough when you have all the right diagnostic equipment on hand and know how to use it. Trying to perform the same task on a motorcycle that is some 1600 miles away involves guesswork of the highest order. Not only that, you didn't mention any specific components when you stated that you "swapped out some parts from a friend's bike." So, given the limited information I have to work with, I believe that the throttle-position sensor (TPS) on your 2001 Gixxer either has gotten out of adjustment or has failed altogether.
Although the ECU at all times knows engine rpm, the current gear in use and other data relevant to proper running, it cannot provide the correct fuel mixture and spark timing without also knowing how far the throttle is open. That is the job of the TPS. I'm not certain about the ECU on your GSX-R, but many on other bikes have a fail-safe mode that will not allow the engine to achieve full power and/or peak rpm if the data it receives is outside normal pre-set parameters. This could explain your engine's unwillingness to rev higher than 11,500.
The shop manual for your GSX-R750 explains how to test and adjust the TPS. Get a copy of that manual if you don't already have one and follow those instructions. I suspect this will lead you to a workable cure for your bike's problem.
