Service

SERVICE

Len Vucci

OIL CHANGE

I own a 1976 Yamaha YZ125. The owner’s manual recommends changing fork oil and transmission oil every three races. Since I don’t race, I’m not sure how often these oils should be changed. Does the oil and gas in the monoshock unit require maintenance? If so, what is required, and how often is it necessary?

Kevin Osterberg Deary, Ohio

Yours are simple, valid questions which defy simple answers. Depending upon who you might ask, the recommended frequency of oil changes will vary greatly.

One basic answer is rather evasive: A change of oil is necessary when the properties of the lubricant degenerate to the point where continued use will result in decreased performance and/or mechanical damage. In simpler terms, change oil before something breaks.

The factories, in general, provide a maintenance schedule which will usually ensure normal component life span. But this is an arbitrary determination, and should be modified as conditions warrant.

Disagreement exists even among CW staff members on this issue, but here’s an almost-concensus: Change fork oil when you can’t decide whether the front end or your body is going soft. Have the monoshock serviced when you’ve made all the suspension adjustments you can possibly make, yet the rear end doesn’t work as well as it once did.

Transmission oil changes should vary with usage. The factory says wide-open conditions like racing mean you should change oil every few hours of use. We’d extend that a bit and say if you ’re a fast trail rider, play it safe and change the oil every 12 to 15 hours of use. If you’re easy on the machine, a change every year will get you by safely. A nd for usage between these extremes, you can do the changes every month or every two months or whenever you think it’s time.

A QUESTION OF GAS

I recently purchased a 1976 Yamaha XS500C and would appreciate your recommendation as to the proper grade of fuel to use. The owner’s manual makes no mention of this. My dealer said premium. The road test in your June issue recommended low-lead in the text (or unleaded or premium in a pinch). The data panel in the same article stated premium.

Bill Laidley Orinda, Calif.

Yamaha dropped the compression ratio of the XS500 engine from 9:1 to 8.5:1 in 1976 in order to allow the use of no-lead gasoline. Therefore, that’s the ojficial recommendation.

But as the miles pile up, so does carbon inside the engine. Many engines supposed to run well on no-lead develop a taste for premium.

We suggest you carefully check the ignition timing. Then, if the engine runs happily on no-lead, use it. If it pings, knocks, etc., switch to premium. The factory reps say premium won’t do any harm.

KZ650 REPORT

I enjoyed your early 1977 road test of the Kawasaki KZ650, and am thinking of purchasing one. I do not know any KZ650 owners and therefore cannot obtain any independent opinions of the motorcycle.

I am interested in the results of your 10,000-mile test of the KZ. How is its reliability, what repairs were necessary, what modifications, if any, were made, and how does its performance compare to any 750s you’ve encountered?

Larry Bogan Hobart, Ind.

Our long-term KZ650 is doing quite well, although we spend so much time putting new equipment on it that the miles aren’t rolling up as quickly as we'd planned.

Halfway through the test the hike has performed without flaw. It’s been dropped once (not by one of our riders) and it’s had one flat tire, but those are the only repairs to date.

Our local Kawasaki dealer, Champion Motors, Costa Mesa, California, tells us the factory has issued a bulletin calling for replacement of the rubber blocks under the cam chain idler gear, and we’ve noted a running change in the carburetors since our bike was built, from fixed idle circuits to circuits which can more easily be adjusted.

We’ve added a pair of S& W shocks, which we like, a set of Preston Petty hex grips, ditto, and we’ve changed to a KZ900 ignition advance curve to get away from a fiat spot just off idle. All the changes work nicely.

The bike is now wearing a Bassani 4-into1 collector and muffler. We're still working with jetting on that change and we hope to have a complete report next month.

As you'll see in the 10 Best Bikes article elsewhere in this issue, we like the KZ650 a lot. Oh, and it’s far quicker than the average 750s we meet.

SYNTHETIC VS NATURAL

I recently read an article in an S.A.E. publication (Automotive Engineering, June, 1977) which reported on a series of tests on Mobil-1 synthetic oil. The Mobil-1 compared favorably with 20W-50 mineral oil in such aspects as hot performance, cleaner engines and reduced wear. It is stated that the lighter weight synthetic oil would give improved cold-start capability, extended drain intervals, peppier running and improved fuel economy. Would you recommend the lighter weight 5W-20 synthetic oil for motorcycle engines? I have a Honda CB360T.

Larry Simeone Somerville, Mass.

The nature of our business normally limits us to relatively short-term testing of vehicles, using lubricants recommended by the manufacturers.

To a man—excuse me, to a person—our staff uses petroleum-based lubricants in its vehicles. The reason is simple: Why spend $4/qt. for synthetic oil, when name-brand petroleum distillates can be bought by the case for as low as 49$ /qt?

We don’t mean to infer synthetic oil is without merit—quite the contrary. Many successful professional racers are using synthetic lube for the slight edge received.

But those of us who try to maintain a budget will go “oil natural”—at least ’til the synthetic’s price comes down.

RD350 GAS CONSUMPTION

I am satisfied with the 1973 Yamaha RD350 I just bought except for its fuel consumption. The best it has gotten has been 29 mpg. My dealer claims the reason is because I ride hard, but I don’t think my riding habits differ from what could be considered typical. Are sub-30 mileage figures considered normal for this bike?

David Dodson Lexington, 111.

Unless you have only two speeds—on and off—your RD’s fuel consumption is on the low side. Our test of the 1973 RD350 produced an even 40 mpg, and you can bet those miles were put on in a very enthusiastic manner.

Without knowing the condition of the engine, it’s hard to say what could be causing the deficiency. Inspect and rule out, if possible, obvious problems like leaky fuel lines, fittings and carbs. Then proceed to a float level and jetting inspection, accompanied by a thorough tune-up.

Finally, if those attempts are unsuccessful, check the engine's top end, including cylinder, piston, rings, heads and base gaskets and reed valves. >

Unless your bike has been geared down, or its odometer is far out of whack, you should be able to increase its mileage substantially.

LOST CHARGE

I recently acquired a Honda CT90 K3, and I am continually having trouble getting it started. The battery is usually so low that 1 must push-start the bike in my driveway. I have checked the electrical system but could not find anything wrong. Can you help?

Tim Wiedman Portland, Ore.

If the electrical system is not at fault the battery is.

JUNGLE FAVOR

I noted with interest Mr. Wesley Ditzel’s letter in your May “Letters” column, in which he relates having trouble finding an oil seal for his Zundapp.

Here in Amazonas, where we live in the jungle, we perform maintenance on quite a varied collection of motorcycles. Our task is made somewhat easier by the nature of parts listings in some of the European workshop manuals. Jawa/CZ manuals, for example, list bearings and seals not only by part number but also by size. Just as one would procure a needed bolt according to length, diameter and thread type, seals and bearings can be ordered by their international standard measurements.

When one becomes accustomed to this method of component replacement, much of the difficulty in locating parts is eliminated. In addition, there is usually a substantial financial savings when parts are purchased from a bearing/seal supply house rather than a motorcycle parts shop.

I have seen as much as a 400 percent difference in price on seals, for example.

Clinton B. Thomas Urucara, Amazonas Brazil >

INFORMATION REQUESTS

While living in Italy I purchased a motorcycle which was used for basic transportation. It is a 1954 Iso 125. and it has a single-cylinder and a three-speed transmission.

I brought the bike back when I returned to the States, and have been unable to locate any information about it. I would appreciate any help you can offer.

Dr. Allen Appelstein, DVM 241-20 Northern Blvd. Douglaston, N.Y. 11363

I have a 1957 Triumph 500 Canadian Militar)'Model with 1691 actual miles. It is in excellent condition.

Can you help me determine the current value of the bike? Where and how should I advertise it?

C.L. Sloan 909 Ave. C West Bismarck, N.D. 58501

I owm a 1966 Harley-Davidson/Aermacchi short-stroke factory road racer. A valve broke, and the head was destroyed. I am unable to make repairs, as I cannot find needed parts, specifically, a head and piston.

Can you give the location of a supplier from which I can purchase these items?

Barry Berto 249 E 5th North Vancouver B.C. Canada V7L-1L8

Anyone?

AIR ROAR

Our August evaluation of the S&W Air Adjustable shocks for the Honda G LÍ 000 quoted a suggested retail price of $95.90. The price, correct at the time that issue went to print, has since been increased to $105.50/ pr.

We hope this bit of inflation doesn’t severely inconvenience prospective AA buyers. 0