The Service Department

THE SERVICE DEPARTMENT

JOHN DUNN.

Due to the tremendous volume of Service Dept. mail, we are unable to reply to individual letters. We shall continue to answer as many as space permits in this column.

A REAL TURKEY

I am in the armed forces stationed near Istanbul, Turkey, and have just recently taken delivery of a 1965 Honda Super Hawk, which I ordered direct from the factory. I assembled the bike right out of the shipping crate. (There is a Honda dealer in Istanbul, but in name only. No mechanics are familiar with Hondas.)

I’m having difficulty getting the engine to run properly at low rpm. I have followed instructions carefully but to no avail.

Here are the symptoms: With engine running at idle — 1000 to 1500 rpm — throttle opened quickly — engine stalls. It sounds like it is sucking air, but no gas. I removed the air filter hoses and when 1 opened the throttle 1 could see gasoline mist coming, out the back of the carburetors rather than being sucked down into the cylinders. Once the rpms are built up — over 3500 — it runs like a top and will take all the throttle you want to turn on.

While actually riding the bike in any given gear, say 2nd, with engine at approx. 2000 rpm, it will run fairly smooth, but just a slight increase in throttle and it starts sucking air again. If 1 close the choke approx. 3/4, it smooths out; then as rpms increase, the choke must be opened accordingly or it will flood. When the engine reaches approx. 3500 rpm the choke is completely open and it will run smooth all the way up to at least 55006000 rpm (1 haven’t gone any higher as the engine is still so new). 1 realize that it would be much easier to take it to a competent mechanic, but of course that is impossible. (I don’t trust the local people to work on a lawn mower.)

Where is the centrifugal advance weights? The operating manual says to make sure it does not stick — well that’s fine. However, 1 can’t find anything that might stick!

Mark J. Nye APO New York

It is almost certain that the trouble being experienced is due to blocked pilot jets or drill ways. At one time the factory was using a special rust preventative in the fuel tanks of machines for export. It was found in many cases that a hard setting sediment was forming in the small pilot passages and jets. It was necessary to completely flush out the fuel system, also dismantle and clean carburetors. Someone had to install new pilot jets as the sediment could not be removed without damage to the jets.

The centrifugal ignition advance weights are integral with the camshaft driven sprocket assembly. The contact breaker cam position is controlled by a shaft passing through the hollow right hand camshaft, this shaft being actuated by the centrifugal advance weights contained in the camshaft sprocket assembly. The contact breaker cam is held in the retard position when the engine is not running. Rotating the contact cam would quickly indicate any sticking.

BUT WHICH IS RIGHT?

1 have a few questions that 1 would like to ask you:

1) Is there anyone who makes a linkage to convert a Triumph to left foot shift?

2) How do the top riders feel about adjusting to the different controls on British and Japanese machines?

3) Why doesn’t the motorcycle industry standardize the controls on their machines?

Patrick J. Heath Glendale 22, Mo.

This is one aspect in motorcycle design and layout where we feel the Japanese manufacturers have taken a retrograde step. It is a medically accepted fact that both reflex and coordination are sharper when the conventional British layout of controls is employed. To coordinate one’s left arm and right foot, as when changing gears on a British machine, is a more balanced and natural movement than using both left hand and left foot when using a Continental or Japanese layout. This also applies when using front and rear brakes simultaneously.

(Continued on page 26)

Using the right foot to brake is much easier for people who are car drivers and just learning to ride motorcycles.

The majority of professional racers adopts the British layout, and when using a Continental or Japanese machine they would make the necessary conversion.

We fully agree it would be a very desirable step for all manufacturers to standardize the layout of controls on their motorcycles.

Sorry, we do not know of any “off the shelf” conversions for changing the Triumph gear change location from right to left.

USE DISCRETION

I own a Honda CB-160 and 1 want better performance on the street. I realize the extreme weight problem, about 17 lbs. per horsepower, but 1 can’t see much that could be carved away. Short of a new frame, it would not be easy to make it lighter. The compression ratio is only 8.5:1, so I think that should come first.

I have access to facilities to mill the head if given the specifications. I believe this is easier than high compression pistons if they are available. Will the milling affect the cam chain tension? I would appreciate any suggestions you could make to improve performance.

1 have thought about supercharging, which 1 realize is a very difficult project with the chain drive, buffer chamber and all, but if 1 were to research it seriously, what would be a likely blower suited to my purposes? With any modifications can it pull the next largest over stock countershaft sprocket? Naturally it will be smoother on the road at lower rpm’s. I’m looking for overall improvement, not just top end. Is the suspension adequate for higher speeds? 1 think that the brakes are.

I would appreciate any and all suggestions.

C. Thomas Graeber Newport, R. 1.

Increasing the compression ratio will give an all-round increase in power output. However, your suggested method of obtaining an increase by milling either the head surface or cylinder barrel, is not without problems. Using this method it would be necessary to alter the piston crown shape to maintain sufficient piston to head clearance and at the same time provide a reasonable combustion chamber shape. It would also be advisable to check the valveto-piston clearance through the valve “overlap” period. An increase in compression ratio may require a change in ignition timing. If a reasonable combustion chamber shape is maintained and shrouding of the intake valve does not adversely affect breathing, it is normally found that a later ignition point can be used. However, if condition of combustion is poor, it may be necessary to use more ignition advance than the recommended standard setting.

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Before carrying out any modifications it must be fully realized that the Honda CB 160 is a highly developed machine, high in the Super Sports category, with a very commendable power output when one considers its relatively small cubic capacity. With a machine of this type it is not easy to maintain the very fine balance of operation that is necessary to obtain high power output combined with good roadability.

Unfortunately, there are no superchargers commercially available, suitable for engines in the small capacity bracket. It may be possible to adapt a small war surplus centrifugal compressor with good results. However, a great deal of research would be necessary to finalize such an installation.

MORE OHCs

Could you please clear me up on something? What new 1966 hike gives the best time in the quarter? Triumph TT Special, Harley XLCH or Royal Enfield TT Interceptor? I don’t care what class it’s in. Consider all bikes stock and broken in.

One more — why aren’t bikes (other than Honda) using overhead cams?

John Maurice Bluhm Morgantown, W. V.

We have not tested any 1966 versions of the machines you mentioned.

It is our opinion that if Honda manufacturers continue to increase the capacity of their machines, it will be necessary for some of their competitors to make radical changes in the design of their products if they intend to survive. The major Japanese manufacturers have in recent years carried out extensive research and development programs with regard to the high speed, internal combustion engine, using to the full, modern techniques in theoretical design principles, material technology and precision mass production methods.

RIGHT APPROACH

1 am seriously contemplating raising the performance of my Honda CB-160 by:

a) Boring it to 190cc

b) Increasing the compression ratio to 10:1

c) Increasing the red line to 12,000 rpm.

By using the formula

HP — BMEP X CU. ln. X RPM 794,000

I arrive at an increased figure of 25 hp (if 1 am correct in assuming that the BMEP is around 150 psi), or an increase of 5.5 hp over stock.

Three questions are conceived concerning this proposed performance increase:

1) Is the crank assembly sufficiently strong to cope with these modifications?

2) Would the modifications necessitate the engine being re-balanced?

3) Is 25 hp a conservative or liberal estimate?

Ronald Marinko San Angelo, Texas We fully commend your scientific approach in the search for increased horsepower from your CB-160. There is, unfortunately, a great deal more involved than shown by your simple formula. It is true that if the right figures are used when making up the values of this formula, an impressive output is guaranteed. However, to achieve the desired figures in practice is no easy task. The most elusive is being able to achieve a reasonably high BMEP figure as the value of rpm increases. In other words, the engine has to be able to breathe efficiently at the peak rpm chosen.

If you could maintain the same level of Brake Mean Effective Pressure at 12,000 rpm on the 190cc engine, as that obtained on the 160 at 10,000, a maximum of approx. 23 bhp could be expected, less the increased mechanical losses entailed by the higher rpm.

It is true that some gain in BMEP will be achieved by your suggested increase in compression ratio. However, this increase would only be a small percentage of that required to boost the bhp to 25 as intended.

Your main effort will have to be aimed at increasing the breathing efficiency of the intake and exhaust arrangements. Larger intake valves, intake tracts and carburetors are a must. A camshaft with radical timing characteristics will be necessary, if only to maintain the mechanical harmony of the valve train at the higher rpm.

Providing piston weight is kept to a minimum, we consider that the crankshaft assembly and main bearings will cope reasonably well with the increase in load. The crank assembly should at least be balanced to compensate for the increased weight of the pistons. It may also be found necessary to alter the balance factor in respect to the increased rational speed.

To obtain 25 bhp or an approx. BMEP of 150 psi would not be impossible considering your intended layout. The end result, if this were achieved, would be a motorcycle engine only suitable for road racing, having practically no bottom end or mid-range torque.

We do feel that you have the right approach by employing theoretical principles and would encourage you to proceed, providing that you have suitable facilities at your disposal. We would like to see more riders follow your example and educate themselves in the theory of the internal combustion engine. We, as a breed, could only profit from this.

SPACE FRAME

I am interested in building a space frame for the Honda S-90. My only problem is finding accurate dimensions for the engine mounting holes.

Will the factory release blueprints? Who would 1 write to for such information, and how much would it cost?

I will appreciate all information you can provide.

Bob Munro Portland, Oregon

It is very unlikely that the Honda Factory will release any of their blueprints, even to a reliable distributor, unless their policy in this respect has changed recently.

However, the dimensions you require would not be difficult to obtain from a Honda S90 engine. ■