Service

SERVICE

JOE MINTON

Rich and flameless

I recently purchased a 1978 Kawasaki KZ650, and it runs so rich that it needs new sparkplugs about every 50 miles. It has air-screw type carbs fitted with what seem to be original main and idle jets. I’ve lowered the needles to the fourth of five positions, ensured that all fuel and air circuits are unclogged, and that all four cold-start enriching valves are sealing properly. The bike has 16,000 miles on it and doesn’t burn oil, but all the plugs go equally fluffy-powdery-black before fouling. I’ve adjusted the float level even lower than my KZ650 Clymer manual specifies. The ignition and spark advance seem to be fine. I don’t know the history of this bike, but I feel it could be a fine piece of equipment if I could just work this one problem out.

Troy R. Miller

Memphis, Tennessee

When all four sparkplugs soot-up equally, it means the problem is caused by something that equally affects all four cylinders. This should eliminate the ignition as the source of your grief, because the KZ650 has, in effect, two separate ignition systems, one for the outer two cylinders and another for the inner two. So, if one of the systems were delivering a weak spark, only tM>o sparkplugs would foul.

The cause also is unlikely to be a failure in the carburetors; the odds of > all four carbs developing exactly the same problem at the same time are astronomically high. Of course, the previous owner could have radically changed the jetting for some reason, but you claim that the jetting is stock. Nevertheless, you should compare the actual hole sizes of your bike ’s jets to those ofproperly sized new jets to ensure that yours have not been drilled out.

Another possibility is that your KZ650 has a clogged intake system.

To check it, remove the air-filter element and make sure the air-supply path is unobstructed from the initial inlet opening all the way to the carburetors. Then, with the filter still removed, take the bike for a short ride.

If the performance improves, you ’ll then know that your plug-fouling problem is being caused by an air-filter element that somehow has become obstructive. If paper-element filters get wet, for example, they tend to shrivel and become restrictive when they dry, even though they may look perfectly clean and normal.

A plugged-up exhaust could also be the culprit. You didn’t indicate whether or not your KZ still has the stock exhaust, so I can’t offer explicit advice. But any significant restriction in the exhaust system can cause the exact symptoms you describe. The causes of restrictions can range from baffles clogged by carbon deposits to aftermarket mufflers pushed so far onto the exhaust pipes that the mufflers ’ internal baffles partially obstruct the pipe openings. An easy way of testing for a restriction in the exhaust is simply to put your hand just behind each muffler outlet and rev the engine vigorously; you should feel a strong flow of exhaust gases rushing from each muffler every time the engine revs up.

You ’ve done a good job of tracking this problem so far. Don’t give up; you ’ll eventually find the solution.

Frigid Twins

I am the proud owner of a 1986 Honda VT1100 V-Twin. This is the second one I’ve owned (the first was an identical ‘85). I have 7500 miles on this one, and since new it has had poor throttle response until the needle climbs to between one-quarter and midway on the temperature gauge. My ‘85 had identical symptoms, and in both cases, Honda dealers have told me this problem is inherent in the VT1 100 and that they can’t correct it.

I’ve tried adjusting the idle speed and richening the idle mixture, but it has not helped. The bike is virtually useless during the winter because it takes so long to run up to temperature, even stationary. Is there a cure?

Mark R. Rubano Marion, Iowa

Your analysis of the problem is correct: The engine in your Shadow is running lean. But fiddling with the idle circuit won’t provide the answer. Rather, the carb needles and/or the needle jets need to be changed.

Honda does not supply alternative carburetor parts; Dynojet, however, makes dozens of different carb kits for most contemporary production bikes, including your 1100 Shadow. The content of Dynojet kits varies from one model of motorcycle to another, but they usually contain new needles and needle jets, plus main jets and any other parts required to cure the kinds of problems you describe.

Your dealer should be able to obtain a Dynojet kit for you through one of his suppliers. If you have trouble getting a kit from a dealer, contact Dynojet directly at 800/992-4993.

The kit for your bike is part number 1116, and its retail price should be somewhere around $65 to $70.

Ring around the Beemer

I own a 1985 BMW R80. During my last sparkplug change, I was able to get a tiny trouble light into the top end of each cylinder, where I noticed that the top of the cylinder walls had a narrow band of dark streaks. These streaks looked like some sort of deposit ringing the very top edge of the cylinders. The walls below that were absolutely clean. I have used only one kind of motor oil (Castrol) in the engine during its 55,000 miles, and I’ve always changed it at 2000to 3000mile intervals. What is this deposit? Does its presence indicate something amiss? Is it possible to remove without dismantling the engine?

Dave Walter Minneapolis, Minnesota

There is nothing wrong with your BMW. The deposits you observed are normal and are composed of carbon and other combustion by-products.

Deposits of this type would accumulate everywhere on the cylinder walls were it not for the constant wiping effect of the piston rings. But the very top of the cylinder does not benefit from this wiping action because the top ring of the piston is located about a quarter-inch from the top of the piston, So, even as the piston passes through Top Dead Center, the top ring cannot wipe that last quarter-inch or so of cylinder wall. Thus, a narrow band of deposits accumulates at the very top of the cylinder.

Don’t be concerned about these deposits unless they become very thick. If that occurs, their presence could lead to preignition and, eventually, the destructiveness of detonation. Heavy deposits (of more than about .040-inch thickness) generally result from the presence of excessive oil in the combustion chamber and usually are an indication of poor oil-ring seal or worn valve guides. Otherwise, normal carbon deposits tend to be self-limiting in thickness, because they are blown away by the turbulence of combustion before they have a chance to pile up.

The agony of da seat

I recently bought a 1985 Honda VF500F Interceptor and have found that it has a broken valve stem and a cracked valve seat. The service manager at the local dealership said that the valve seats are made into the head and cannot be replaced. Is that true?

If not, how can the seat be replaced?

David Templeton

Goldsboro, North Carolina

The valve seats on the VF500 were indeed pressed-in at the time of manufacture. They can be replaced, but only by a highly skilled person with the proper equipment and the knowledge of how to use it. Very few motorcycle shops are capable of doing the job correctly, which is the main reason why Honda does not supply replacement valve seats.

I’m sure there are many cylinderhead specialty shops that can perform this delicate operation, but I only know of one: Gatlin Racing (714/563-0747) in California. If anyone out there knows of other outfits that can do this kind of work-and do it properly-please let me know so I can keep their names on file for future reference. O