Service

SERVICE

Enough is enough

My Honda CBR900RR is a great bike and has plenty of power, but I’d like to change the pipe and maybe the air cleaner to “open 'er up” a little. A friend tells me that I shouldn’t do this because the new pipe will mess up the tuning of the carbs. Is this so?

Edward Trumble Tucson, Arizona

Chances are that you 'll gain very little power with an exhaust-pipe change; in fact, you may even lose some power, depending upon which pipe you install. And you will almost certainly need to retune your carburetors, a difficult task on a 900RR or any other modern fourcylinder motorcycle.

Two decades ago, in the heyday of the original Honda 750 and Kawasaki Z-l Fours, much power could be gained by bolting up an aftermarket pipe and installing a less-restrictive air cleaner. That isn 't so true anymore. Most latemodel motorcycle engines have such highly developed intake and exhaust systems that it is exceedingly difficult to hot-rod for additional horsepower without also forcing major performance compromises elsewhere in the rpm range. Mostly what you 'll gain is noise, and loud bikes pose a bigger threat to the sport today than ever before. Modifying the intake and exhaust without negatively altering the power and noise outputs is possible, but not by any simple bolt-on method.

Rich and stuck-up

I have an ’89 Yamaha FZR1000 with only 1700 miles on it. The last time I rode it, it ran rough and had black smoke coming out of the exhaust. When I asked my dealer about this condition, he said that because I had allowed the bike to sit for so long between rides, the carbs had gotten gummed up with old fuel, causing the engine to run extremely rich. He said the only way to correct the problem would be to replace the carbs. Is this true? If not, what can I do to fix the problem and prevent it in the future?

Doug Stenger Banks, Oregon

Replace your dealer; not the carbs; he 's probably right about the carburetors being gummed-up, but he s deadwrong about the need for new ones. The solution is to clean or replace the parts that are gummed up, not throw away the entire bank of carbs.

When a bike sits unused for months at a time, the fuel in the carburetor float bowls evaporates, leaving behind a gummy residue that can clog the jets. But only the jets located in the float bowl-the fuel jets-are affected; the air jets are not in the float bowl, so they don 't get clogged by the residue. And when the fuel jets get clogged, an engine runs too lean, not too rich.

In your case, however, the black smoke is evidence that the engine is indeed running too rich. And while it's highly unlikely that the fuel jets are clogged, the residue could have affected other curb components. If one of the four float needles or cold-start "choke" valves has gotten gummed up and is sticking open, a rich-running condition would result. If the culprit is a sticky float needle, you should notice fuel pouring from the float-bowl overflow hose behind the engine. If there are no fuel overflow problems, then check to see that all four of the coldstart enrichment valves close completely when the choke is turned off

If you aren 't able to track down the cause of the problem yourself take the bike to another dealer or a reputable motorcycle repair shop. A fter a thorough carburetor cleaning and adjustment-and possibly the replacement of some of the smaller jets-your FZR should run like new.

To prevent this problem in the future, drain the float bowls any time you suspect that you won't be riding for a month or more, and put some fuel stabilizer in the gas tank. The float bowls can 't gum up if they 're empty, and the stabilizer helps prevent the gummy residue from forming in the tank.

Bucking Kawabronco

My ’86 Kawasaki Ninja 600 is driving me nuts. Every time I get on it real hard in first or second gear, it acts like it’s either skipping a tooth in the transmission or jumping in and out of gear. The bike bucks back and forth a couple of times as it starts accelerating, and it makes incredibly loud banging noises that sound like something in the driveline is getting ripped apart. The bike has 16,000 miles on it, but it works perfectly except for this one problem. As long as 1 don’t try a dragstyle launch or a firstor second-gear wheelie, it never misses a shift or pops out of gear or does anything weird. My dealer has replaced the clutch and the rear-wheel drive cushions, but the problem hasn’t gone away. He says the next step is to tear the engine down and check the transmission, but 1 don’t want to spend all that money unless I have to. Dorn DeMarco

Elyria, Ohio

If the rest of your Ninja is as mechanically sound as you say it is, check the drive chain very closely before going to the expense of having the engine removed and disassembled. If you 're still using the original chain, it 's likely to be stretched beyond its service limit, which means that fullthrottle, firstand second-gear acceleration could he causing it to jump over one or two of the rear sprocket teeth. That would result in exactly the symptoms you describe.

To check the chain, grab it at its rearmost point as it wraps around the rear sprocket and pull it directly rearward, as though trying to yank it off of the sprocket. If you can lift it almost the height of a sprocket tooth, the chain is worn out. Chain adjusters nearing the end of their usable range are another indication that the chain needs replacing.

If the chain has been jumping the sprocket, the sprocket teeth will show telltale signs of wear, maybe even to the extent that the very tips of the teeth are bent forward. If you see any of these symptoms, don 't take chances: Replace the chain and both sprockets.