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 CB750F SWING ARM
Would it be possible to interchange the nylon swing arm bushings on the 1979 CB750F Honda with the 1980 CB750F needle-bearing swing arm pivot?
Recent inquiries with American Honda Motor Co. were hopeless because of legal obligations. I hope you can provide me with an answer to my problem and if not. is there a solution?
Chris Colivas Boise. Idaho
The latest needle roller bearings are not interchangeable with the 1979 bushings because the pivot is a different diameter and the frame mounting holes are changed.
However, Yoshima offers bronze bushings which are almost as good as needle rollers, to replace the plastic ones. Contact Yoshima at Ontario Moto Tech Corp, 6850 Vineland Ave, #18, North Hollywood, Calif. 91605.
HALOGEN HONDA
1 own a 1975 Honda CB550F on which Eve installed a Bosch H4 headlamp. 1 ride
the bike mostly on weekends, about 20 to 50 miles. To keep my battery charged I put on a switch so 1 can use the starter.
The problem is that when I use the QH lamp I can't ride more than 20 miles because my main fuse burns or pops out and when I try to replace it I always have to wait a minute so it can cool down.
I have checked all the wires, terminals, switches, charging system and headlamp connections. Everything is okay. The only thing I moved was the starter switch. Please tell me what I can do?
Jess Alvila Salinas. CA
When you refer to a starter switch we assume that you have installed a switch to disconnect the headlamp when you are starting the bike. That 's a good idea because the H4 Bosch draws Jive amps (60 watts at 12 volts) and the battery can do with all the help it can get when coping with the load of firing up the engine.
However, there is ample capacity in the Honda's battery and charging system to handle a 60 watt bulb and it shouldn't blow
fuses in 20 miles.
The main fuse can normally take the current of a QH headlamp so there must be a short in the circuit somewhere. We suspect that it's in the starter switch you've Jit ted. Try isolating the switch by using a pair of insulated connectors instead and run the bike for a few miles. If it works, you've found the fault.
Bikes made in the past couple of years have been using automatic circuits that switch on the headlamp only after the engine is running. You might find that these are interchangeable with your 1975 Honda.
ELECTRONIC YAMAHA
I am the proud owner of a 1977 Yamaha XS750-2D and I’m told that no one but Yamaha makes an electronic ignition for the bike. Can you help?
Rick Roberts San Diego. CA
Yamaha switched to a magnetically triggered coil ignition for the 1978 model Triples, which knocked the bottom out of that continued on page 147
cleaner. This is a solvent that will remove the shellacs and varnishes that can upset the mixture. It can obtained from most auto parts stores and dealers under a variety of brand names.
Best wav to clean the exhaust pipe bajfies is to burn off the carbon deposits with a gas torch and then clean them up with a wire brush. You can also dissolve the carbon off in an alkaline solution but this can be very4. dangerous because the solution can burn the skin.
The service manual shows the torque curve and specific fuel consumption at full throttle. Since you ’ll be running at much lower throttle openings than full, this curve doesn’t apply. The engine is happy at any speed between 3000 and 4500 rpm for touring but remember, the faster you go the more gas you 'll use, not because of the torque curve but because of the throttle opening.
KAWASAKI CARBS
I own a ’75 Kawasaki Z-l which I re-i cently had tuned. I was told my carbs are worn out. It was also said I couldn’t get original carbs for my bike anymore. Could you give me some addresses in which I could get original carbs? Or could you suggest better carbs for my bike.
Gary Hill Biloxi, Mo.
It’s surprising that the carbs should be worn, but then you don't mention the mileage. Nevertheless if you do need a re-' placement set of Mikunisyou 're in luck. For 1979 Kawasaki switched back to the 28mmehoke units used on your 1975 model, butf with different idle metering and main jetting. These should run better than wheq your original carbs were new.
My Honda CB750A Hondamatic has an electrical system failure problem. I have talked to numerous owners of '76 to ’78 750A Hondamatics and almost without exception they too are experiencing blown 15-amp main fuses. When this fuse blows everything including the engine quits dead._______>
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bike's aftermarket ignition system sales.
Being a three-cylinder engine with crank throws at 120°, the XS750 requires three triggers, which complicates the system more than a four-cylinder system ihat can use coils that double up for each pair of cylinders.
Delta Products (630 South 7th St., Grand function, Colo. 81501) offers a capacitor discharge ignition system that uses the XS750-2D's original contact breaker points. Since these points only have to break a current of 0.3 amps, instead of the usual two to three amps, pitting and erosion of the point faces is minimal. Life of the point heel pubbing on the cam can be extended (to 50,000 miles, claims Delta) by polishing the cam and correctly lubricating it.
All the advantages of capacitor discharge ignition remain however, since the circuitry senses the exact moment of point opening and is unaffected by points bounce.
BRIGHTER TRIUMPH LIGHTS
My motorcycle is a 1979 Triumph 750 Bonneville. 1 note that the headlamp bulb now fits into a three-prong socket which appears identical to the standard automotive set-up (instead of the old push-and(wist number). It looks as though I could just take out the whole unit and plug in an automotive sealed-beam, scrapping the pilot light. If it would work mechanically, would the electrical system handle the extra wattage? Or better yet, could I plug in a quartz-iodine? Lucas makes a quartz H4 bulb ‘P36T’ which looks like it would fit right into my present reflector and lens and ^ave the pilot light.
The stock headlamp is inadequate for any night riding.
A. LoGalbo Woodstock. NY
The Lucas alternator on your Triumph can more than handle the extra load of a 60watt quartz-halogen bulb. The simple replacement of the conventional bulb with the H4 bulb might not necessarily work because the focus may be incorrect for the lens.
The German company Hella offers a complete replacement headlamp and bulb for a Triumph which retains the pilot bulb. Its part number is 186 002 395-162 and the price is $28. For your nearest dealer contact the local distributor: Racemark International, 150 Lake Hills Rd, Burnt Hills, N. Y. 12027, telephone: (518) 399-9106.
CB750F JETTING
I own a 1979 Honda CB750F and have a problem. Recently I installed Racer 1 leaders and separate foam filters. The carbs have been adjusted twice and it’s the same thing over and over again. It's difficult to start when cold and it breaks up at iiigher rpms. Both my service shop and
American Honda Co. say the jets are pressed in and there’s no listing available for different jets. Is there anyone out there who might know of something that might work or will I have to abandon the CVs for some smooth-bores?
Fonnie Hedges, West End, N.J.
The final resort to any need to increase jet size (this only applies to the main jet, idle jets are too small) is by drilling the jet to a larger size. Find a number drill that will just fit the jet so that you can gauge the size accurately, and then start drilling out with the next drill size up in turn until the mixture is correct on full throttle. It means that you 'll have to buy a number of drill bits, but these are cheap.
You shouldn't need to do this with the CB750F however. American Honda Co., like all manufacturers, is worried that by altering the jetting you 'll he violating emissions laws and that they would become accomplices by advising you.
You can change the jets. They are the normal screw-in type, regardless of what you are told by your dealer. The part number for the jet is the same for all sizes so when you order it (the number is 99102-393-1020) specify the size you need.
The correction of the starting fault is more difficult because the idling mixture jets are pressed in and being so small, are virtually impossible to enlarge. As a jirst move try changing your starting technique. The carburetors use an accelerator pump. So with the chokes closed for starting, before hitting the button open the throttles half way and give them a few turns on the twist grip. This should inject enough raw fuel into the inlet tracts to do the trick.
ALL PLUGGED UP
I own a 1977 Suzuki GT750 watercooled Triple. I was interested in the “idle too long” reply in your September issue. I bought the bike in August with 4500 miles on it. The first 4300 dated back to the summer of 1977. I would like to know how to get the shellac or varnish out of the carbs because I have the same lag at low revs as Mr. Johnson. Also, what is the best way to clean baffles? I would appreciate a reply because I am really disappointed in the starting performance of the bike. For a two-cycle, it seems to have the power of a 125 leaving from a stop.
Also, the fuel consumption chart in the service manual shows lowest fuel consumption and highest torque at 6500 rpm. My red line is at 7000 rpm. What would be the ideal engine speed for touring?
Patrick Voigtmann, Kingston, Ont, Canada
Thing to do is to remove the carburetors, dismantle them (while taking a note of their method of assembly) and dunk the components in a pan of commercial carburetor>
I have written to Honda in Gardena. California, to find a remedy to this problem. They simply suggest we go baek to the dealer. Yet numerous poor dealers here in San Antonio and in Houston have told us they don't know what's eausing the problem although they are aware that it exists.
Jack Ramsey.
Helotes, Texas
The problems you describe were caused by wire oj too small a gauge supplying the fuse. This caused the wire to overheat which lead to the fuses not blowing but melting the end connections. Honda has been aware of the trouble and introduced a modification late last year. This was communicated to all dealers. It includes a metric fuse and fuse box (part number: 38200-393-772).
We talked to Honda about your trouble and their Customer Relations Department should have contacted both you and your local dealer with respect to correcting the fault.
UPTIGHT!
Why do you experts continue to tell us Yamaha cast wheels are leakers? I have a XS750E with wheels that say “tube type” and the only différence between them and the ones on my XSl 100SF is the width of the flat surface adjacent to the bead surface. This change was made for faster and easier mounting.
The wheels on my 750 hold air every bit as good as the ones on the Eleven.
The tires on my 750 are tubeless style. Continentals, 3.50-19 front and 5.10-18 rear. In a six-month period the tires lost an average 3 psi measured with the same air gauge and with the tires cold.
Greg Martin Eau Claire, Wis.
We don 7 say that Yamaha cast wheels are leakers. And neither is it because of casting porosity that Yamaha recommends that only tubed tires be fitted to wheels marked ‘'tubed type. "
Wheels for tubed and tubeless tires use different profiles for the rims. These differences, which are important for safety, are only slight to the untrained eye, just a matter of about 5° on the angle of the bead facing, and are easily confused. Tubeless tires use much tighter clearances between the rim and the bead to help seal the tire. And they also need a bead retention lip to ensure that the bead doesn't roll off' the rim if pressure is lost.
Therefore you are running a risk in using tubeless tires on your XS750. Sure they will hold air. Chances are that the set of wheels you have are not porous, though some might be. However, if you pick up a nail or rock, the pressure might not be lost slowly, as it should be, so that you can control your machine. It might deflate suddenly, in the left lane of the freeway. And you know the possible consequences of that. 19
