Service
SERVICE
CYCLE WORLD
Weak-starting Nighthawk
I’ve had to push start and jump start my 1983 Nighthawk 650 several times due to a weak battery caused by the stop-and-go city driving I do. My dealer’s solution for this was a toggle switch to turn off the headlamp and a suggestion that I change my driving habits and rev the engine higher.
The switch resulted in two $35 traffic tickets for driving with the headlight off. Revving the engine helps, but I still wind up with a weak battery, sweaty brow and a painful back. The charging system seems to function normally.
My solution to this is to remove the airbox and battery and put in a 32 amphour battery with a 50,000 mfd capacitor. To avoid having to rejet the stock CV carburetors, I plan to replace them with new high-performance carburetors with K&N air filters. Will my solution damage the electrical system? And where can I find the aftermarket carburetors?
Johnathon Cohen
New York, N.Y.
The larger battery won’t hurt the electrical system, but it won’t cure your problem. All 1983 650 and 550 Nighthawks were supposed to have electrical systems that had a 1500 rpm break-even point; that is, at any engine speed above 1500 rpm, the battery should be charging. With that low a break-even point, the battery shouldn’t run down even in urban traffic.
Unfortunately, the break-even rpm was often slightly higher than 1500 rpm, and the break-even calculation didn’t account for the use of turn signals and brake light. In stop-and-go use, many 1983 Nighthawks ran their batteries down. Honda has come up with a fix that consists of a modified alternator with higher output, and the fix is covered by your warranty. Your dealer should be able to install the new alternator, and if you have any problems with warranty coverage for the procedure, contact Honda’s local customer relations office at phone number (609) 778-1100.
Fastest 550 GPz
i/ust read your April test of the 1984 GPz550 and I agree with your test. This is one of the best engines ever produced. However, didn’t Cycle World test the 1981 GPz550 at 12.65 seconds through the quarter-mile? Because the 1984 had the same times, how can you say it produced more power?
Eric D. Coobs
Billings, Mont.
Kawasaki claims the 1984 GPz to make more power, 65 hp. compared with 57 hp. for the 1982 550. Why isn’t that power difference reflected in our quarter-mile testing? First, the 1984 GPz is geared taller relative to its peakpower engine speed, and that detracts from its quarter-mile times. Second, while there may be more power at peak, there is slightly less at other speeds, and that results in slower acceleration, particularly in the lower gears. Third, our dragstrip tests of the two bikes were performed years apart, and, as quartermile times can vary by a few tenths of a second due to track and atmospheric conditions, perhaps these times simply aren’t the best comparison of the capabilities of these two bikes.
All that said, we suspect there isn’t an eight horsepower difference between our 1982 test bike and our 1984 test GPz. The two-mph higher top speed of the newer bike indicates some power increase, but, perhaps because of production variations, it isn’t eight horsepower.
Mobil 1 and motorcycles
I own a 1983 Honda 650 Nighthawk.
Eve considered using Mobil l synthetic oil in the crankcase, and I wonder if any damage will result. Would there be any detrimental effects long-term or shortterm? Also, is there any reason Mobil l couldn’t be used as a final drive oil?
William Fink
Milwaukee, Wis.
Honda recommends the use of lOw40 engine oil in the Nighthawk. Mobil 1, a 5w-20 oil, is thinner than this recommendation, and we would be hesitant in using it in the Nighthawk. No immediate damage would necessarily occur, but bearing load capacities would be somewhat reduced, and that would make us nervous. It makes Honda nervous, as well, and the use of a lighter-than-recommended oil could void your warranty.
Mobil 1 (or any other engine oil) should never be used for a final-drive oil. The hypoid gear oils intended for the final drive contain special additives that help preserve the faces of the gear teeth when they scrub against each other at very high pressures. The additive packages in engine oils are different, and they’re not as good for lubricating gears.
Safe cruising rpm
IVhile riding at high speed through the eastern Oregon desert last summer, I became concerned that I might be maintaining a cruising speed that was too high for the safety of my engine. As I understand it, redline is safe only for short-duration bursts.
I recall reading in an auto magazine that safe cruising rpm can be determined by piston speed as expressed in feet per second. Is this still a valid concept? Does it apply to motorcycles? What is the safe limit? What would it be for my VF750S?
Bill McElfish
Beaverton, Ore.
Redline on Honda motorcycles is the maximum safe cruising rpm. The far end of the red zone on the tach marks the maximum speed the engine should ever see.
While safe rpm levels for sustained operation may he related to piston speed, there’s no one piston speed level that’s safe for all machines. That depends on the details of the engine design. The manufacturer’s recommendations (given in the owner’s manual) are the best indicator of an engine’s capabilities.
For your reference, piston speed in feet per minute is calculated by multiplying stroke length (in feet) by rpm times two. Your Sabre’s pistons are traveling an average of 3350fpm at 10,000 rpm. That’s not an excessive piston speed by any means, as there are some streetbikes running at over 4000 fpm at their redlines, and racebikes that approach 5000fpm.
Boyesen reeds
Ê was reading your article on making the IT250 perform and was interested in the part about reeds. I would like to know if Boyesen makes fiber reeds for the RD350-400 Yamahas. Could you send me their address?
John Hodge Christiansted, St. Croix
Boyesen does make reeds for the RD Yamahas. They sell for $17.95 per set, and two sets are required. Boyesen Engineering’s address is Rd. No. I, Box 826, Lehartsville, Pa. 19534, and their phone is (215) 756-6818.
More flywheel for the KDX200
I have a 1984 KDX200 Kawasaki and would like to know if there is any way to add weight to the flywheel or if there is a heavier flywheel from another bike that would fit. Could I add the weight myself, and if not, who could do it?
I’d like for the bike to lug more on the bottom end.
Jim Simons Butler, Penn.
More flywheel would make the KDX easier to ride in many tight, slow-going situations, but the heavier-flywheeled bike would accelerate slower, the rear wheel would be harder to break loose for quick turning, and there isn’t an easy way to increase the flywheel weight. We don’t know of another flywheel that would fit, so adding additional weight to the existing flywheel or crank are the only options.
A good machine shop could add a oneto two-pound steel disc to the side of the existing ignition flywheel. The alternator cover would have to be spaced out to clear the new material. Another way to add weight to the flywheel would be to screw and epoxy a steel ring to its outer diameter. Clearance between flywheel and case would limit the weight that could be added.
A heavier flywheel increases loads on engine main bearings, and increases the twisting loads on the crank. Those effects can be avoided by adding weight to the crank. Two large holes can be drilled in each crankshaft half, each 90° away from the crank pin. The steel removed could be replaced with tungsten crank-balancing material that’s more than twice as heavy. Approximately a pound could be added this way.
Any of these approaches to increasing flywheel effect are likely to be expensive, and will require the services of a good machine shop. The machine shop you want will do motorcycle or car racing work at least as a sideline, and will talk your language. To locate such a shop, check the yellow pages, and ask local mechanics or racers.
CB1100F wobble fix, continued
In a letter in the May Service column, Lars Pedersen described how tightening the steering head bearings on a CBl 1 OOF to 87 ft.-lb. eliminated wobble. Unfortunately, that torque is entirely too high for the steering head bearings, which are adjusted by a ring nut under the top triple clamp. The 87 ft.-lb. figure applies to the steeringstem nut that holds down the top tripleclamp. Torqued to this high value, the steering-stem nut presses the top tripleclamp down onto the bearing adjusting nut hard enough to increase the load on the bearings, and that load increase is what eliminates the wobble. The same effect can be achieved in a more suitable manner by tightening the bearing adjusting nut to Honda’s recommended torque setting of 8 to 9 ft.-lbs. ®
