The Service Department

THE SERVICE DEPARTMENT

PERFORMANCE RACKET

JOHN DUNN

Every time a group of motorcyclists gathers, the subject of increasing engine output invariably comes up. As night follows day, someone always states the first step to performance is removal of the muffler or replacement with a megaphone, etc. Please settle a universal argument which, if I am correct in my convictions, will also boost public relations for cyclists by reducing the racket associated with cycles.

I contend that most, if not all, motorcycles produced for sale to the general public will not benefit (performance-wise) by muffler alterations. In fact, the performance of some machines may even suffer. How about an article on this subject to clear the air?

John A. Moore Ex canaba, Mich.

If Service Department had a nickel for every question in regard to replacement of standard mufflers with megaphones and expansion chambers on street bikes, this magazine could probably promote a successful nationwide program with the theme, "Noise is Good For You." And that is the very least CYCLE WORLD would have to do to support the many motorcyclists who believe: "If it's loud, it's bound to be fast."

By now the CYCLE WORLD policy on noisy exhaust systems should be clear to anyone who has read more than a couple of issues. The magazine does not condone loud exhaust systems on street bikes, but condemns any motorcyclist who modifies the exhaust system of his street bike in such a manner as to produce a louder exhaust noise than it did in standard form. There is little doubt that raucous megaphones, expansion chambers and straight pipes are major contributors to the case the non-motorcycling public has for years been attempting to build against the sport. It's evident, then, that a rider who chooses to operate a noisy motorcycle is damaging the sport and thereby harming himself.

If this argument against loud exhaust systems seems a bit abstract, there is another consideration-performance-that strikes closer to home. Some years ago, motorcycle manufacturers paid little, if any, attention to refining exhaust systems. Like as not an éngine was developed with an unmuffled exhaust system and, after everyone in the works was satisfied with its performance, the engine would be put into production, installed in a standard frame, and fitted with a muffling device that was designed to keep the noise at an acceptable level, even if it cost a few horsepower. It was not surprising, then, that removal of the muffler would yield extra power and improved performance. But, this was some years ago. More recently, engine development programs have been characterized by more sophisticated and complete approaches to the matter of obtaining high performance levels from production engines, and a noteworthy area that has received a great deal of attention is quiet, efficient exhaust systems. Tuning is now a fine art.

It is quite true that removal of the muffler and addition of a megaphone will not increase the performance of a standard street motorcycle unless the engine is tuned to accept the change of exhaust system. And, in most cases, to properly tune an engine for an open exhaust requires a change of camshaft, compression ratio, valve and ignition timing, and even alteration of valve angles, enlargement of ports and valves, and changes in the length of the inlet tract. H arle y-D avid son recently has experimented with an ultra quiet silencing device, and has accidentally gained 5 bhp. By reducing the decibel output of the exhaust noise, a rider may actually increase the performance of his machine.

SUPER TRAILER

I am toying with the idea of making a cow-trailer, using my Super Hawk engine. Before I come to a decision, I want to arm myself with a few pertinent facts. Number one, do the Rickman brothers offer a Metisse motocross kit to which the CB 17 enginetransmission unit could be adapted? If not, is there a Yetman motocross frame which would do the job? Additionally, are there cams available which will give the Super Hawk engine good low rpm torque? I wouldn't mind losing a couple of thousand rpm at the top end if the bottom was suitable for trials riding. Incidentally, if it is of any significance, my Super Hawk is a '68 model. Provided that all the answers are favorable, how much of the Super Hawk's standard equipment would I need for the trailer, and do you think the idea is basically sound, or should I just sell the Super Hawk and get a Matador? I have a natural proclivity for four-stroke twins.

Ernie Aubert San Jose, Calif.

I do not believe the Rickmans produce a Metisse specifically for the CB 72 or 77 Honda engine transmission unit, but the Yetman Corp. does make a frame expressly for the Super Hawk engine. However, I do believe that the Honda unit could be installed in a Rickman frame without much trouble. You asked if this idea is basically sound. Well, that would depend on the individual. The finished product would be just as heavy as a 650-cc Triumph Metisse. Some people would prefer the light weight of the Matador. This would be for you to decide.

I would stay with the CB pistons to start, but try the C 77 camshafts with the CB 77 valve springs. It would be nice to have a single carburetor instead of the dual instruments found on the CB. However, in spite of this, I (Continued on page 18) would stick with the CB cylinder head with the large intake valves and look into the possibility of applying a single carburetor manifold in conjunction with one of the 26-mm carburetors. Relating back to the C 77 camshafts, it would be necessary to remove a locating spline from one of them in order to suit the 180-degree crankshaft of the CB 77.

Continued from page 16

There would be a lot of work involved, but I do think it would be well worthwhile building a hybrid CB 77 Metisse for trailing.

K-70 PROBLEM

I've just put 2400 enjoyable miles on my brand-new Suzuki T-305 in the past month. However, I've had one problem which may interest your other readers-and maybe U. S. Suzuki. When I ordered the bike, I ordered K70 Dunlops front and rear, and feel that they are worth the extra cost. But the K-70s create a problem—they are slightly larger in cross-section than the standard tires and, after about 2300 miles (many with my wife as passenger), the rear tire chewed its way through the wires routed under (or inside) the rear fender to the taillight, causing a short circuit and three blown fuses before the dealer figured out the problem. We rerouted the wires on top of the rear fender (about a 15-min. job). I now have set the rear shock absorbers on "hard" position so that the tire won't rub against the spot-welded wire brackets under the fender.

I was lucky that I was in town and in relatively good weather when the problem became apparent (when I turned on the lights while the engine was running)-but luck is a poor substitute for reliability. Perhaps you'd print this (or part of it) to alert other riders-and maybe get Suzuki to put out a service bulletin for T-305 and Hustlers. For all I know, this could happen to riders of other brands. I certainly will be more wary when I change tire brands on any bike from now on.

Thomas B. Fitzpatrick Seattle, Wash.

You have brought up a very useful point here, Tom, especially when you consider the vast number of riders who install oversized tires these days. Apart from causing damage to wiring and the danger of being run down from behind, due to failure of the taillight or stop light, there is also a danger of tire failure, particularly at high speed as the result of tire overheating.

Getting back to this oversized tire business, I quite frankly cannot see the point in fitting tires that obviously will detract from good handüng characteristics. I can see the point in changing the make of tire or making a small change in size to suit individual taste, but this big tire thing seems to be a very erroneous performance image, obviously started by some very misinformed individual or group. I would be very interested to hear from some of our readers who have gone the oversized tire route, giving the reasoning behind it.

RESTRICTION?

I recently purchased a new 750-cc Matchless (Norton) Scrambler. It came from the factory with low exhaust pipes. The pipes were no good for cross country riding, so I spliced the right exhaust into the left, in a graceful Y shape about even with the crankcase breather. The tailpipe now runs above the chain case. Question: Will the single pipe cause too much restriction? I am running one muffler with the rear of the inside cone drilled out.

Dan L. Fletcher K.I. Sawyer AFB, Mich.

The two individual pipes are most suited for optimum high speed performance. However, a good all-around performance can be obtained with a siamesed system, providing it is sensibly proportioned. As a guide, primary lengths should be 15 to 20 in. The secondary length can be of the same diameter, providing it is not exceptionally long. The siamesed system will usually give good low speed torque characteristics, particularly when a fairly radical cam is employed, for good high speed performance.

Why don't you compare the performance of both systems over a measured distance to obtain some idea of the efficiency of the new system?

CAUSTIC COMMENT

I own a 50-cc two-stroke motorbike. The bike is 11 months old. I just bought a new header for it because the other was full of carbon, and it cut the power drastically. The new header is building up carbon, and I don't want to go out and buy another one. Could you please tell me the way to clean the header? I have always used Steens C oil.

Mark Mandala Glendora, Calif.

Mix up a strong solution of caustic soda in (Continued on page 20) a suitable container. Remove the complete exhaust system from the machine and submerge in the solution for several hours. Remove and wash thoroughly with water. Take care not to get the solution on your skin, as it will burn or cause irritation. If all the carbon has not dissolved, repeat procedure. This method is also very effective for decarbonizing cylinder heads or barrels, providing they are made from ferrous metals. Do not clean aluminum parts in this way, as they will become severely damaged.

Continued from page 18

Caustic soda also will remove all paint from any part treated. With cylinder heads and barrels, quickly grease all machined surfaces after washing with water to guard against rust. The caustic will thoroughly degrease all parts.

PLONKER PLAGUE

I have a '66 Ducati 250 scrambler. I just installed a set of standard rings. I had less than a 0.001-in. taper. I had the valves ground, and they are set at 6 and 8. New points and condenser were installed. The points are set at 0.012 in.

. I was advised to put a small sprocket on to seat the rings, which I did.

In Montana, trail riding, the engine idled well, but at slight throttle it sounded like a twin firing on one.

I have the needle on the lowest setting, and a 112 main jet. Everything is standard, the way the cycle came.

I have a 70-tooth sprocket on. I used to be able to plunk real good with this set-up, but now I foul plugs running slow.

I am not running a battery, as the repair shops here claim I don't need one because I'm not using a lighting system,

I bought a repair }nanual and it says running without a battery could affect the stator plates. What is your opinion on this?

The timing was checked with a degree wheel anda timing light.

Frank Morley Spokane, Wash.

You state that you are fouling plugs when running at low rpm. However, you do not state whether it is oil or gas that is causing the problem. Inspection of the plug should give a definite indication. A cylinder bore taper of 0.001 in. is nothing to worry about; some new machines will have as much. When installing the new rings, did you make sure that they were correctly fitted, with sufficient end gap, and that their top faces were facing upwards? The smaller rear sprocket would impose more load on the engine, and create high cylinder pressure to insure ring seating.

The main jet size or needle position would have little or no effect on the mixture strength at plonking speeds. It is more than likely that an over-rich mixture, result of a high fuel level or poorly seating float valve, is causing the wooly running at low speeds.

Regarding the statement in the works manual regarding running without a battery: Follow factory advice.

LACKS JUICE

I own a 1967 Honda CB450 with approximately 3500 miles on it. Recently I was having problems keeping the battery charged (I still am), and while trying to inspect the electrical system, I removed the alternator cover. I noticed a large amount of oil begin to drain out. The local mechanic said that this was normal. As I'm in Vietnam, and don't exactly rely on what mechanics tell me here, I'd like your opinion. Also, what could be wrong with my electrical system that would cause my battery to run down and not want to hold a charge? I do very little night driving and therefore seldom use my lights. I've had the battery checked out and there is nothing wrong with it.

I've been toying with the idea of removing the head gaskets from my bike in order to gain more compression. Can this be done without leakage? If so, what are the torque specifications? Also, if this idea is not feasible, what is the maximum I can mill the heads and still get my piston clearance?

Michael F. Shaw Philco Ford Corp.

APO San Francisco, Calif.

The alternator on the CB 450 is partially submerged in the engine oil. Removal of the alternator inspection cover with the machine standing upright will result in loss of oil. If the alternator cover has to be removed, lay the machine over toward the right-hand side.

During daytime running (with lights switched off) only one coil of the generator is in operation. The generator output at 5000 rpm is 2 amperes, with a tolerance of plus or minus 0.5 ampere. It may be necessary to have the generator checked to be sure the output is within tolerance. When running, the ignition system will use between 0.5 and 1.0 amperes. The generator in proper condition is easily capable of meeting these demands. However, the rear brake light does consume a considerable amount of current, and if the (Continued on page 24) brake light switch is incorrectly adjusted, or you are in the habit of riding with your foot on the brake, the battery will become flatthe result of an insufficient charging rate under these conditions.

Continued from page 20

Do not discard the cylinder head gasket. If the cylinder head is milled in order to obtain a higher compression ratio, it will be necessary to remachine the squish area back in the head to insure that there is adequate piston crown-to-head clearance. It also will be necessary to check the valve-to-piston clearance. Milling the head also will result in the valve timing being retarded. An excessive amount milled from the head will result in the timing chain tension system becoming unmanageable, unless the chain is shortened. Before making modifications of this magnitude, give it some serious thought.

TIRE PRESSURE

It seems to be common knowledge that auto manufacturers' tire pressure recommendations are compromised in the direction of soft ride to the detriment of handling. I realize that the dynamics of motorcycle tires are considerably different from those of car tires, and I consequently wonder how adjustments in pressure will affect motorcycle handling. But never have I heard or seen a discussion of tire pressures for motorcycles.

Specifically, would a change in tire pressures benefit the handling of my Suzuki X-6? It is newly equipped with Avon Speedmaster Mark Ils front (2.75-18) and rear (3.00-18). The original Inoue tires seemed to be of a much stiffer construction, aside from using a rock-hard non-cling rubber compound. Incidentally, the Avon rib, when brand new, is 0.5 lb. lighter, and slightly smaller in diameter than the Inoue of the same nominal size after 17,000 miles of hard wear. The Avon also seems to distort more at the pavement, and squashes to within nearly an inch of the rim when I ever-so-gently roll the bike over a curb to park it at night. This is using the factory recommended 23 psi. At the rear, Suzuki specifies 25 psi solo, 30 two-up. I run 30 at all times. I do a great deal of "ear 'oling" and high speed touring. Clip-ons keep the weight bias forward. What should I do, and what are the principles of setting the pressures in general?

Ben English Albany, N. Y.

This is a very controversial subject, Ben, and when you get right down to brass tacks, the final decision usually rests on individual preferences that are not based on any particularly defined principles. There are manufacturers' recommended pressures that advise a safe operating range. The pressures you have quoted are well within this range unless you are in the 200-lb.-plus weight bracket. I would advise 22 to 25 psi in the front and 27 to 30 psi in the rear.

It is an accepted fact in racing circles that tire pressures have an effect on tractive resistance and that the highest possible pressure should be used, bearing in mind some degree of comfort or whether the road is wet or dry. With modern cling compounds that permit higher pressures, some road racers inflate their tires to 34-36 psi.

It therefore is a matter of individual taste within reasonable bounds. Experiment with various pressures and suspension rates until you are satisfied.