Service

SERVICE

Adventure in lighting

Paul Dean

This past May, I purchased a 1998 KTM Adventure Rally. I am happy with the bike and have 2300 miles on it, but I'd like to make a change to the lighting system. The low beam has a nice, wide spread with good peripheral coverage, and the high beam has more of a pencil-type pattern with good long-range illumination but poor pe npheral coverage. I'd like to change the wiring so that both beams are on in the high-beam position. I've ridden with the high-beam flasher button depressed for up to five minutes at a time and had no apparent problem. Can the electrical system handle having both lamps on continuously? Scott E. Kerbs Napa, California

On paper, the bike `s charging system should be able to cope with the added load; the Adventure Rally has a 200watt alternator and about 180 watts of total current demand with all lights-in cluding both beams-in operation. Here's an easy way to find out for sure: Disconnect the negative battery terminal and clip a heavy jumper wire between the end of the ground cable and the ground terminal on the bat tery. Then also connect a 10-amp am-

meter between the cable and the bat tery, with the positive lead of the am meter clipped to the battery and the negative end attached to the cable. Start the engine, and as soon as it set tles to idle, disconnect the jumper so that all current flow is measured by the ammeter. With the brake light on and the turnsignals in operation, hold the high-beam flasher switch in the On position and gradually increase engine rpm until the ammeter starts showing positive amperage. You will then know that any time you are riding the KTM at that rpm or higher, the battery will be receiving a charge, regardless of which lights are in use. If the rpm is low enough to keep at least a minimal charging current flowing during your normal riding, the battery will not discharge; if the rpm is too high, however, it would not be advisable to have both beams operating simultaneously.

Carb conundrum

I recently purchased a well-worn `76 Honda CB750. The bike had been sit ting for at least three years, so I didn't even try to start it until I cleaned the carbs. When I pulled them off, I found that the float stand on one had been broken off and the other three floats were badly damaged. Fortunately, I had a wrecked `83 Honda 550 Nighthawk in the shop, so I pulled and cleaned its carbs and installed new float needles, and they bolted right up to the 750.

The problem is that when I try to ride the bike, it does fine as long as I slowly roll the throttle open to about 4000 rpm, then the engine bogs and backfires through the carbs. If I feather the clutch and am real patient, it will pull through this period and rev to redline. I can get it to run better if I leave the enrichener on, but then it won't idle below 3000 rpm when it's warm. The condensers, points and plugs all are new. The valve clearance is right. Spraying oil around the intake mani folds does not change the rpm at idle. Spark quality is good, there is com pression in all cylinders and fuel in all four float bowls. My father and I are at wit's end chasing this problem. Have any suggestions? Sean Berry San Antonio, Texas

The symptoms you describe all indi cate an excessively lean fuel mixture. That's not surprising, given that the CB550 s carburetors were not cali brated to provide the correct mixture on a CB750. The Nighthawk's carbs are 30mm constant-velocity types, whereas the 750's are 28mm slide needle units. And internally, there are considerable d~fferences in the sizes of the various metering devices-main jets, pilot jets, needle jets, jet needles, slide cutaways, etc.

It is possible, of course, to get the CB550 carbs to function properly on your GB 750, but doing so will require either the adjustment or complete re placement of some of those metering devices. Based on your description of the problem, the 750 seems especially lean in the middle rpm ranges and at partial throttle openings; this indi cates that either the jet needles need to be raised or replaced with richer ones, or that the throttle slides need to be swapped for ones with a lower cut away in the rear-or perhaps both. In all likelihood, you `11 also have to in stall larger main jets and idle jets to get the engine to carburate properly at all rpm and throttle positions.

Heavy breather

Town a 1974 Harley FLH that still has the stock oil feed and return in the primary case. Can I block off these ports and just run a few ounces of oil poured directly into the chaincase? Is this as beneficial as I have been told, and is simply plugging the oil ports the right way to accomplish it? Tom Ramsey New Smyrna Beach, Florida

This modification can be done, but not as easily and simply as you describe. The plumbing in the chaincase is a vital part of the engine breather system; if you block it off the engine won’t be able to breathe, resulting in smoking and loss of oil. And because the primary drive is lubricated by oil vapor emitted from the breather rather than by an actual oil bath, the material on the clutch plates is designed to run dry. If you put sufficient oil in the case to adequately lubricate the chain and sprockets-and doing so will require more than just “a few ounces’’-oil will also get on the clutch plates and cause slippage. So, if you make this breather modification, you ’ll have to change to a Barnett “wet’’-style clutch designed to operate in oil.

I suggest you find a good, reputable Harley mechanic in your area and have him make the breather modifications. Not only is the routing of the breather hoses too complicated to explain in the limited space available here, but a 25-year-old Harley is likely to have had its breather system altered in some way. Better to have an expert look at it up close and personal. □