Service

SERVICE

Mean green vibe machine

Paul Dean

I have a 1996 Kawasaki ZX-9R that I bought brand-new. I've always treated the bike properly and serviced it according to the manual in regard to things like valve adjustments, carb synchronization, etc., but it has begun to vibrate badly. When I allow the engine to brake the bike, the vibration gets real bad as the rpm reaches about 4000. And at normal highway speeds, which have the tach reading around 3800 rpm, my hands go to sleep in about an hour. Have there been any complaints of this sort about the ZX-9R?

H. Szautner Posted on www.cycleworld.com

ZX-9R engines are not known for their exceptional smoothness, but neither do they normally vibrate as badly as you indicate. My guess is that the excessive shaking can be traced to any one of several problems. Start by checking all the motor-mount bolts to make sure they're properly torqued. There are sev eral bolt sizes involved, including those that attach the 9R two removable down tubes-which also house the front motor mounts-to the main frame structure. Since there are afew different torque values to deal with, I suggest you buy a shop manual. It uses illustrations to ident~fj~' all the bolts and lists their re spective torque specs. If any of these bolts are even a little loose, the engine can move around just enough to transmit more of its normal vibration into the frame and the rest of the chassis.

Also carefully check the entire exhaust system for the tightness of its mounting hardware, and inspect the system closely for cracks and splits in the header pipes, the collector, the muffler and all the mounting brackets. If the exhaust is loose or broken, it, too, will vibrate excessively and pass that shaking on to the chassis.

Last but certainly not least, inspect the final-drive chain and sprockets. If the chain is excessively worn or improperly adjusted, or if the outer edges of the sprocket teeth have been worn to a sharp point, they could create their own vibration frequencies that ultimately get fed into the chassis.

Jet setter

I'm thinking of putting a Vance & Hines pipe on my Yamaha YZF-R6 and I want to know if I'll have to rejet it. Buying the bike almost cleaned out my bank ac count, and the pipe will pretty much take care of the rest, so I don't want to pay for rejetting if I don't have to. I just want the bike to run a little faster and sound a little better. The local Yamaha shop says that I won't have to rejet if I put on the pipe, but a racer buddy of a friend of mine says I will. Who is right?

Larry R. Coughlin Sparks, Nevada

I get quite a few letters much like yours, Larry, and the vast majority of them could be given the same answer: Even if you don’t bolt on a new pipe, your bike ’s performance will benefit from the proper installation of a jet kit. Similarly, fuelinjected models generally will perform better with a remap of the fuel curve in the ECM (engine control module), even if the stock exhaust system is retained.

For the past 20 years or so, motorcycles have been jetted not to produce optimum performance but rather to comply with the mandatory emissions regulations in effect during their year of manufacture. Consequently, they all have lean spots throughout their various fuel-metering systems, so they all could benefit from adjustments in the air-fuel mixture. There are a few aftermarket pipes available that give good results without any carburetion changes, but those bikes would run even better if they were rejetted.

I can’t tell you how well any given pipe will perform on any given motorcycle unless I have tried that combination myself or worked closely with someone who has. For the same reasons, neither can I tell you if installing that pipe on that bike will call for any jetting changes. Since I have no such experience with a Vance & Hines exhaust system on a YZF-R6, I can’t tell you whether or not you will have to rejet. All I can tell you is that if you want to extract the best performance from that exhaust system, you should rejet.

Death by magnetism

With the proliferation of fuel-injection systems and their requisite in-tank fuel pumps on today's motorcycles, is there any chance that the magnets securing my magnetic tankbag will cause damage to the pump? I own a Suzuki TL1000S on which the fuel pump is located toward the back of the tank, and the rear mag nets in the bag rest just a few inches forward of it. What's your take on this matter?

Tony Lottus Posted on America Online

I've never heard any reports of magnetic tankbags causing problems with in-tank fuel-injection pumps. The magnets are capable of erasing data on floppy com puter discs stored in the bag, but they `re not powerful enough to affect the fuel pump in any way. The magnets exert a fairly strong pull on the outside of the gas tank, but the strength of the magnetic field on the inside of the tank is prac tically nil. If the magnets were powerful enough to affect the pump inside the tank, you d need a fork l~fi' to remove the bag from the outside of the tank.

The condensed version

Just recently, I bought a 1978 Kawasaki KZ1000 LTD basket case that had been sitting outside for about eight years. After cleaning and reassembly, the engine ran fine for a while and then the number 2 and number 3 cylinders began misfiring. Repeated cleaning of the fouled sparkplugs only yielded the same results: It would run fine for a while and then numbers 2 and 3 would cut out. Checking the set of breaker points that fire those two cylinders revealed that they were not consistently making contact when closed; so I would clean them, after which those same two cylinders would work for a while, then quit again. I then replaced both sets of points (not the condensors) but still got the same results. Would a bad con densor cause the points to "foul" that quickly?

Pat Anderson Cheyenne, Wyoming

Absolutely. The condensor prevents electrical current from jumping across the gap-or "arcing "-every time the points are opened by the breaker cam. That arcing causes the contact surfaces of the points to become burned and pitted, creating an electrical resistance that reduces the amount of current that flows through the points when they `re closed. That subse quently reduces the amount of current that reaches the coil~ primary windings, which, in turn, results in a weaker spark generated in the coil's secondary windings. Pitted contact surfaces also cause the ignition timing to vary from one firing cycle to the next because the actual point at which the circuit opens is not consistent.

Since electricity always follows the path of least resistance, a condensor attached to the positive side of the points eliminates virtually all arcing. At the instant the points open, the current finds it easier to flow into the condensor than to jump across the gap. So, the points open cleanly, with only a tiny, almost imperceptible arcing across the gap.

One-track mind

I was trying to explain, to a buddy of mine who doesn't ride, about counter steering. I told him about how, if you want to go left, you push on the left bar, which causes the front wheel to turn slightly to the right, and the bike goes left. What I couldn't do is explain why. Can you help me out?

Brian Wandro Posted on wwwcycleworld.com

Considering the tiny amount of space I have here, that’s kind of like asking for the history of the world in 25 words or less. But I’ll give it a shot anyway.

When you turn the steering wheel of a car to the left, the chassis leans to the right as centrifugal force attempts to keep the car going straight. Well, precisely the same thing happens with a motorcycle: When you turn the handlebar to the left, centrifugal force causes the bike to lean to the right. The difference is that the car turns left as it leans to the right, while the bike turns right as it leans to the right.

That difference is the result of a car being a two-track vehicle and a motorcycle being a single-track vehicle. A simple way to demonstrate this is to simulate a singletrack vehicle by standing on one foot, then have someone push sideways on either of your shoulders; they don’t have to push very hard before you tip over. The only way you can resist falling is to lean inward, toward the person doing the pushing. But if you simulate a two-track vehicle by standing with your feet spread about a yard apart, you ’re much harder to push over. You ’re now supported by a wider base that allows you to resist falling over, even when you are leaning outward, away from the person doing the pushing. This difference is what allows a car to turn in one direction while leaning in the other, but forces a motorcycle to turn and lean in the same direction.

There isn’t enough room here to delve into all the other dynamics of motorcycle handling, such as the need for a rider in a corner to constantly balance centrifugal force, which is trying to make the bike sit up, with gravitational force, which is trying to make it fall down. But I hope this simplistic explanation has given you at least a basic insight into countersteering.

Con-rod killer

My ’97 Yamaha YZF600R has the local mechanics scratching their heads and my wallet losing weight at an alarming rate. The problem is that it sometimes refuses to start. The starter will crank the engine over for about half a second, then it stops instantly with a loud metallic “clunk.” Subsequent attempts to start it only deliver a click but no rotation of the engine when I use the starter button, and neither will it turn over when I try to push-start it. Yet, the very next day, it will start and run just like new.

I took the bike to the shop and they replaced the starter clutch, but when I went there to pick it up, the starting problem reoccurred. During their second attempt to find the problem, they discovered that the fluid level in the crankcase was too high, caused by gasoline getting into the oil. Further diagnosis revealed that the electric fuel pump was allowing gas to leak into the engine at idle, thereby creating “hydrolock” pressure within the engine such that it couldn’t turn over. A new fuel pump and an oil change cured the problem for about three weeks, but then it returned.

I’m at a complete loss, and so are the mechanics. Could you please let me know your thoughts about the cause of

this problem?

Scott !hi111ps Posted on www.cycleworld.com

The problem is not in the fuel pump; it’s in at least one of the carburetors. And the flooding does not occur while the engine is idling; it happens while the engine is off and your YZF is parked.

Whether or not a bike has a fuel pump, the flow offuel into the carb ’s float bowls is controlled by each float’s needle-andseat. The needles must seal properly at all times to prevent fuel from entering the float bowls once the maximum level is attained. If one of the needles leaks, fuel will continue to enter that carb ’s float chamber while the bike is sitting unused.

In your bike s case, the unwanted fuel that gets into the float bowl was in the fuel line when the engine was shut off and it was still under slight pressure from the fuel pump. As that fuel spills up and out of the float bowl, it drips down into theintake manifold. If the intake valve is open while the bike is parked, the fuel runs directly into the combustion chamber, then gradually leaks past the piston rings and down into the crankcase. This usually doesn’t prevent the engine from starting, because the fuel drips into the crankcase at about the same rate that it leaks from the carb into the cylinder. But if the intake valve is closed while the carb is dripping, the fuel cannot enter the cylinder, instead accumulating in the intake port. Then, as soon as the intake valve opens for the first time when you try to start the engine, all that fuel is drawn into the combustion chamber; if the volume of the fuel is greater than the volume of the combustion chamber at Top Dead Center, the engine locks up when the piston nears TDC, because liquids cannot be compressed. This occurrence is called “hydraulic lock,” and it is easily capable of bending a connecting rod, especially when someone attempts to bump-start the engine.

You need to have your YZF’s needles and seats carefully checked and either cleaned or replaced. Otherwise, you ’ll soon be looking at a major engine rebuild to repair the damage caused by a bent or broken connecting rod. □

Got a mechanical or technical problem with your beloved ride? Can’t seem to find workable solutions in your area? Maybe we can help. If you think we can, either: 1) Mail your inquiry, along with your full name, address and phone number, to Cycle World Service, 1499 Monrovia Ave., Newport Beach, CA 92663; 2) fax it to Paul Dean at 949/631-0651; 3) email it to CW1Dean@aol.com; or 4) log onto www.cycleworld.com and click on the Feedback button. Don’t write a 10-page essay, but do include enough information about the problem to permit a reasonable diagnosis. And please understand that due to the volume of inquiries we receive, we can’t guarantee a reply to every question.