The Service Department
THE SERVICE DEPARTMENT
JOHN DUNN
HONDA GAUGE GUIDE
How could I install oil cooler, oil temperature and oil pressure gauges on a Honda CB750? The oil cooler is a Ford power steering unit. The gauges are SW.
I carry a lot of gear on the Honda and drive 140 miles a day, so I assume the above modifications will be worth the effort.
Lee. F. Bevins Pomona, Calif.
To my knowledge, Lee, the Honda 750 Four does not suffer from excess oil temperature. In fact the large oil filter unit which is situated at the front of the engine is nicely located from a cooling point of view. It is also provided with external ribs that act as fairly efficient cooling fins. However, an oil cooler could be hooked into either the oil feed or return lines that run between the engine and the oil tank. It is important that the cooler be of the free flowing type and not produce any more than a 4 psi pressure drop across it.
The installation of an oil pressure gauge is easy, there being an oil pressure checking point situated on the right front side of the crankcase. This point is mentioned in the rider’s handbook. To install a permanent pressure gauge one would have to remove the 17-mm cap nut at the checkpoint and hook up the pressure sensing line to this point.
There is no convenient point for connecting an oil temperature sensing probe. I think the easiest place to install it would be in the oil tank. This would entail either cutting a hole in the front, back or side of the tank to accept the probe bushing or modifying the tank drain plug to accept the probe.
HONDA CARBURETOR HASSLE
After reading your test on the new Honda 450s (CIV, May ’68), I was so impressed I just had to trade my dependable little 160 for a new CL 450. I love the bike even though it has given me all kinds of trouble since new.
I’ve been able to work off all the small problems except for one. Ever since my Honda CL 450 was new it has had a tendency to foul plugs. I tried adjusting the carburetors according to the manual but it doesn’t seem to do any good. I cleaned the filters also. I switched to hotter plugs, which seemed to help for a while. I now have about three heat ranges hotter than standard Honda plugs. The problem continued to get worse until the bike wouldn’t idle, and ran rough at low speeds. I removed the air filters and the bike ran fine for about 1000 miles except for an occasional backfire from the right carburetor and popping in the exhaust pipes.
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Now it is starting to act up again. It won’t idle below 3000 rpm. I checked the ignition system and everything is in order. It has new points and the timing is right on the mark. The carburetors are clean and the vacuum slides are free to move. I don’t know what to do now except maybe change to smaller jets. This should make the fuel mixture leaner, shouldn’t it?
Brian K. Williams Cobden, III.
It is possible that your CL 450 is one of the earlier ones that suffered from certain carburetion problems. Honda brought out a special “fix” kit in an effort to cure them. Clean your carburetors externally before dismantling them. Remove the top of each carburetor. The later models are equipped with long, light springs that slip over the vacuum-operated throttle valve to insure that it always returns to the fully closed position when the throttle is shut. If your machine is not equipped with these, buy and install a pair. It may be necessary to purchase the complete “fix” kit. If you have been operating the machine with the air cleaners removed, it is almost certain that the close fitting throttle valve has been contaminated by dust and dirt. It is most essential that this type of carburetor is operated only with an efficient air cleaner. The throttle valves should be absolutely clean and be able to slide freely in their bores. Inspect them carefully for burrs or embedded foreign particles.
The ignition advance mechanism is situated behind the contact breaker assembly on this machine. It is subjected to considerable heat and receives very little lubrication, which causes it to stick in a partially open (advanced) position during low speed operation. This is not good for favorable idling conditions. However, the offending unit can usually be freed without dismantling anything by squirting a suitable lube through a hole behind the contact points by means of an aerosol can.
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If you use your machine mainly for pottering around town, I suggest that you use a grade B8 spark plug. Conversely, if the machine is continually driven hard the colder BIO spark plug is recommended.
NO SPUNK SPRINT
/ recently purchased a 196 7 HarleyDavidson Sprint Model SS. It’s top speed is about 65 mph. As far as I know it is not leaking compression. How could I make my Sprint go faster and increase the horsepower? The motor runs well and it is very tough. Could you tell me approximately what it would cost to get a full race cam?
Dan Springer Lake Luzerne, N. Y.
The performance from your HarleyDavidson Sprint is below par. Its top speed in standard trim should be more than 65 mph. Under favorable conditions it should be capable of between 75 and 78 mph.
It is possible that the previous owner has changed the gearing. Check the number of teeth on the gearbox final drive and rear wheel sprockets against the manufacturer’s recommended specifications. If your machine has standard factory gearing it is fairly obvious that engine condition is not up to scratch.
Installing a full race camshaft would definitely be a waste unless the engine is in tip-top condition. Even with the engine in first class shape I would not advise that a full race camshaft be installed, particularly if the machine is going to be used on the street. To make full use of the “hot” cam it is most necessary to have an open exhaust system that is specifically tuned to suit a particular camshaft’s characteristics. An exhaust system of this type would not be legal for street use.
To improve general performance for street applications 1 am more in favor of precision building the standard engine in order to improve its general efficiency. However, to do this successfully requires a great deal of skill and experience, together with a fairly well equipped workshop. A production engine is built to production tolerances. This is why some machines of one particular make and model will perform much better than others of the same model. If you get a machine with components and assembly as close to specifications as possible you end up with the occasionally exceptionally “good one.” It is possible to achieve this yourself by blue-printing an average machine and have a better running combination than if you took the same machine and cluttered it up with so-called racing or performance goodies. However, if you persist, a racing camshaft can be purchased for approximately $35. But the expense does not end there, because to allow the camshaft to do its thing you will require suitable valve springs that in turn have to be installed correctly. Also, make sure that you have sufficient valve-to-piston clearance if you retain the standard piston. In fact, consider the whole thing very carefully before going out and buying that magic “hot” camshaft.
RAKE AND TRAIL DEFINED
I am puzzled over the handling abilities of three types of motorcycle front ends. They are as follows: extended, raked out (not extended), and extended and raked out. What are the advantages and disadvantages of these front ends compared with the regular fork angle?
Robert Lang Apache Junction, Ariz.
There is no simple explanation to your question, there being many unknown factors involved. But it is essential that we define the various terms related to the steering geometry. The two most common terms are “rake” and “trail.”
“Rake” is simply the degree of steering head inclination relative to a vertical line drawn through the front axle. “Trail” is measured in inches or millimeters as the case may be. Imagine a two-wheeler having the front fork and steering head vertically mounted with no rake at all. A machine of this type would be very difficult to ride on anything but a very smooth surface. If the wheel struck a bump, the point of contact would be forward of the steering axis; therefore the wheel would be knocked violently to full lock.
If we allow a few inches of trail, the axle is moved back in relation to the steering column axis. Impact caused by a bump would now exert its force at a point behind the steering axis, minimiz ing the tendency for the wheel to be knocked sideways. However, due to a very complicated phenomenon when employing vertical steering with trail (caster action), the front wheel is likely to develop a violent wobble. On the other hand, if the steering head were angled alarmingly to a point where it was almost horizontal, the machine would have a very strong tendency to fall on its side when the wheel is turned; this would make low speed handling very heavy and awkward. It is therefore necessary to compromise with respect to steering head angle and trail.
Experience has shown that a rake (steering head angle) of between 25 and 30 degrees combined with a trail of between 2.5 to 3.5 in. give results somewhere in the ball park. Although a variation in trail will not dangerously affect the handling of the machine, it will definitely alter the “feel” of the machine. Increasing the trail to, perhaps, a maximum of 4 in. will enhance high speed stability whereas reducing the trail to a minimum of 2 in. will have the reverse effect, giving a lighter cornering characteristic but less feeling of solidity at high speed.
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These are only two of the aspects related to obtaining good steering qualities. The gyroscopic effect of the front wheel, cornering forces, tire size and tire adhesion all have to be taken into account. Another point not understood by many is that the motorcycle pneumatic tire has a built-in tendency to run straight, due to the reaction between the road surface and the resilience of the tread pattern. The tire sometimes tends to resist side forces with such determination that the wheel might swing the opposite way a fraction and then over-correct in the other direction. This oscillation is the beginning of a lock-to-lock wobble. It is also one reason why a machine that steers well with a given tire size may become very unpredictable with a tire of another size although the tire diameter or steering geometry has not been altered. There are a lot of inexperienced riders that just have to change the front tire size even on a new machine, because it just happens to be the current “fashion.”
WHEEL BALANCE PROBLEM
I read your mag every month and really dig the road tests. I've got a 1968 BSA that I bought new in 1969. Lately I've noticed the front tire is getting small flat spots on the tread. A buddy of mine told me that my front wheel needs balancing, butldon't know how to do it. Any advice you can give would help.
Wayne Sumner Fresno, Calif.
Front wheels being out of balance is common on most of the machines on the road today. It is very easy to remedy and most riders can do a satisfactory job at home without special equipment.
First, prop the machine up so the front wheel is clear. Back off the front brake, so the wheel will spin freely. Turn the wheel over slowly until the heavy spot settles to the bottom. Let the wheel revolve by itself, and finally it will stop with the greatest mass resting at the bottom. Directly opposite the heavy part of the wheel, at the top, make a chalk mark.
Wind some wire solder around a spoke and against the rim at a point even with the chalk mark. Add or subtract solder until the wheel will remain motionless when left in any position.
When you have completed the balancing, wrap a piece of electrical tape over the solder to keep it in place. [QI
