Service
SERVICE
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your "Service" letters to technical subjects only, and keep them as brief as possible. Send them to: "Service," CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
HONDA BUSHINGS
I own a new 1979 Honda CB75OK which I am in the midst of converting to a full touring bike. In addition to upgrading and replacing the front and rear suspension. I am changing the rear tire and rim from a 4.25H-18 to a 4.50H-17 for an increase in load carrying capacity.
While the rear suspension is being altered, will the new, improved swing arm and needle bearings from the 1980 CB750 fit my chassis and is the investment worthwhile instead of replacing the nylon bushings with metal bushings?
Bob McJimsey Ponca City, Okla.
There ’s a lot more to the new swing arm assembly than just some bearings added. The entire swing arm pivot and supporting area in the frame is new and the new pieces can 7 fit into the old frames. You can get much better swing arm location by fitting a good quality metal bushing, like the bronze bushings from Ontario Moto Tech. Corp., 6850 Vineland Ave., Unit 16, N. Hollywood,
Calif. 91605 (213) 766-7101. The bronze bushings will replace the plastic bushings with no other modifications and won 7 deteriorate as quickly as the plastic pieces. Bushings are also available from Target Products, 2724 W. Main St., Alhambra, Calif. 91801. Phone (213) 284-3238.
WATER BUFFALO JETTING
In your October issue, Tom Pappas asked about a gas mileage problem with his 1975 Suzuki GT750. Some of your tips were helpful. Others, however, were not.
The GT750 was originally equipped with a dry paper air filter but was fitted with an oiled foam element from 1974 on.
Models from 1975 have different internal and final gearing than the 1972-74 ^models as well as thinner head gaskets and different pisfons. Experience with these machines shows that owners often substitute incorrect parts. Stock final gearing on Mr. Pappas’ machine was 16 tooth countershaft and 43 tooth rear sprockets, but a 15 tooth countershaft sprocket has proven more useful for average riding. An early model head gasket is thicker and could reduce compression from the 140 to 150 psi which is normal.
“Then there’s the carbs.” 1974 and later models were equipped with model BS40 diaphram carburetors. The main jet size for the end carbs is 110 while the middle carb should have a size 107.5. The clip on the jet needle should be in the fourth position from the top in all three carbs. Float level is 27.6 millimeters and the pilot screw opening is one quarter to three quarter turns out from fully seated.
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Finally, ensure that all three starter plungers close completely and equally and that the carbs are properly synchronized.
Barring any mechanical malady, proper gearing and carb adjustment should restore Mr. Pappas’s mileage to around 40 mpg.
Stuart Oltman.
Chicago. 111.
COLD BLOODED SUZUKI
By now you’ve'probably received dozens of letters on this problem, but here goes anyway.
1 have recently purchased a new Suzuki GS850 which I am very pleased with but for a couple of exceptions:
1) The bike's extremely cold-blooded nature.
2) What feels to me as a surging condition when the machine is operated in the upper gears at say. below 4.000 rpm.
Is there anything that can be done to remedy this, short of an expensive carburetor exchange?
Rich Dolhnger Harthorne, N.Y.
Most of the 1979 models suffer from coldbloodedness, that is, taking a long time to warm up, because EPA emissions standards demanded the adoption of weak mixtures, but Suzukis seem to suffer more than most.
Suzuki says that as the miles build up the cold starting should improve. Since the engine is very sensitive, the difference created by bedded-in piston rings and valve seats should be noticeable.
It is possible that the surging is caused by deposits in the metering circuits. These are often left after the rough fuel used at the factory to test the engine evaporates. The cure is to strip the carburetors and blow out the passages with an air line.
Though Suzuki won't specifically recommend it since alteration of the carburetor settings is illegal in some states, the final resort in the perfecting of the mixture is juggling with the jets. Jets for the 1978 models can be obtained from dealers, if necessary.
PERFORMANCE JETTING (1)
I have a 1979 Suzuki GS 1000S and like it very much except for the lean jetting of the carbs (to satisfy the EPA). Please tell me what the stock 1979 GS1000 jets are and what the stock 1978 GS 1000 jets are also. I am considering installing a Kerker header with a street core so what jetting changes would you make? And can I keep the stock slides?
Bvron May
So. San Francisco. Calif.
The tighter emissions regulations were introduced for machines produced after January I, /978. Therefore, the jetting for ir the 1978 GS1000C and the 1979 GS1000N and GSWOOS was the same: 95 main, 02 leedle jet, 5DL36-3 needle, 1.5 slide cutaway and a 15 pilot jet. The only difference u between 1977 and 1978 was the use of an 04 needle jet to riehen the mid-range. However, the use of the richer needle might not necessarily work since different pressed-in air correction jets were used in the earlier niodel.
Regarding the Kerker exhaust system, , Kerker doesn 7 specifically recommend changing the jetting, but say that you might 0prevent the pipes blueing by richening the mixture. It wouldn't give you any more power though.
He must warn readers that they might be violating state law by altering the emissions systems on their motorcycles. Federal law makes it illegal for a company or a paid >mechanic to change jetting, hut many states still allow an owner to do so. A t the moment,
the chances of being caught for changing jetting are remote because no inspections are made. But check on your local laws all the same.
DISCOLORING PIPES
I have recently installed K & N air filters on my 1978 KZ650 Kawasaki and I am now in the market for a 4-into-l header. I would like to install a chrome header but I’m concerned with the problem of discoloration of the pipes. Is this a problem ircommon with all brands of headers or is the engine at fault? Are there any ►solutions?
John Nichols
Baltimore. Md.
Because of the high temperatures encountered in the exhaust systems of mot orcycles, a chrome plated pipe will always discolor. (which is a form of oxidation) >unless the plating is protected from the heat. Most motorcycles have double-wall header
pipes fitted at the factory that get round the problem, the notable exception being BM W, vthose pipes invariably blue within the first few miles of operation.
* Such a form of construction is expensive <and adds weight however, and aftermarket manufacturers of header pipes rarely, if ever, use double walls.
He don't know of any surefire way of overcoming the problem.
