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,” C YCLE WORLD. 1499 Monrovia Ave., Newport Beach, Calif. 92663.
NOT ENOUGH CHARGE
I own a 1976 Honda CB400F on which I’ve installed a Dyna-III electronic ignition. It’s keeping the battery discharged, to the point that the electric start and turn signals won’t work. A fast workout on the highway will cure this, but only for an hour or so. The battery isn’t the problem. Dyna-III told me the ignition draws three times the amps of the stock ignition, but shouldn’t affect the battery. Have you any information on how to cure this problem?
Jerry Turgeon,
West Covina, Calif.
Your problem may not be the battery or the ignition. If the electronic unit draws three times normal amperage, that would be 9 amps. Maximum charge rate for your 400F is 13 amps. The battery should be getting its share.
Have you checked your wiring diagram? Could be the Dyna-III is wired wrong, and is creating a current drain the alternator can't make up for. Or, if the battery is in good health and the ignition isn't taking too much current, your alternator or regulator are at fault.
COLD PLUGS
I have a tip which might benefit your readers. I own a Yamaha XS400F. When I went to change the oil for spring, I found the drain bolt was stuck tight. I tried the correct metric socket, vise grips, pipe wrench, even beat a standard socket onto the bolt. All I was doing was tearing metal.
Then an auto mechanic friend asked if I'd used Freon, the gas in car air conditioners. We got a Freon tank with a control valve and sprayed the bolt with the gas for about 30 seconds. I clamped it with a pipe wrench and the bolt almost turned itself.
The Freon is so cold that it chills the metal, which shrinks the bolt and makes it easy to turn.
Be careful where you spray, though, and be sure to wear goggles and gloves. If the gas hits you, it can cause frostbite.
David Hamblin Cincinnati. Ohio
JETTING BY GUESSWORK
I’ve been very interested in articles about carburetion. I own a Honda 750 bored to 810, with Presholite ignition. 10.5:1 c.r., a hot cam and (soon) a 4-into-l exhaust. The engine has the stock Keihin carbs.
None of the parts manufacturers recommended anything about jetting. I’m ad-
vised to buy Mikuni smoothbores (expensive) and then I'm told to rework the stock carbs.
Apparently seat-of-the-pants is the common method for carb jets, but I can't see makingfour changes if one is the proper way.
Mike Luma Castalia, Ohio
Tuning by guess is the way it's done, even in professional circles. The difference between pro tuners and the rest of us is that they have the experience on which to base their guesswork.
But even seat-of-the-pants can be done in the proper sequence.
The adjustable parts on your carbs are the pilot jet, the slide cutaway, the slide needle and the main jet. As a guideline, the pilot controls mixture right off idle. Then the cutaway takes over beyond about oneeighth throttle. The needle position rules the mid-range, with the main jet working at wide open throttle or fast cruising.
The secret here is first, begin at the bottom. When the idle is set and the carbs in sync, experiment with the pilot jets. One step at a time. If you're lucky, you can keep the stock slides. When the response at light throttle and low speed is right, read the spark plugs and try raising the needles. One notch at a time. When the mid-range is right, make some power runs and read the plugs and go up on the main jets. One step at a time.
That's how it's done. Repeating: make only one change at a time, and if you go too far, go too far toward rich.
EASING THE BUMPS
I ride a 1976 Honda CB400F, stock except for slightly higher bars. I'm satisfied with the bike except when it comes td' bumps. When I cross railroad tracks, raised surfaces, etc., I get jarred to the point of loosened teeth. What can I do that will smooth out the ride without altering the handling?
Michael A. Fox Rochester, N.Y.'
What you need is more progressive suspension. Check the parts catalogs, Honda o f accessory, and find some softer fork springs. Then add air caps and experiment with pressure. You'll have the normal spring rate most of the time, and stijf springs when you need them. If this alters damping too MUCH,A change fork oil weight until you 've got a grade that suits the spring rate. (At $1.5(1 per can, it's the cheapest way to alter damping.)
In back, a good set of aftermarket shocks and perhaps progressive rate springs, will help. Keep in mind, though, that you don't have much wheel travel, which means making them stiff enough to prevent bottoming is also going to give a firm ride the rest of the time.
STALE START SECRETS
I have a Honda CX500 and am extremely pleased with it except for one thing. If it sits five days or longer it be-t comes a slow starter, taking quite a few cranks to get fuel to the cylinders. If it only' sits a couple of days, it will start almost instantly. What procedures or alterations will cure this?
Ron Hollett Sharonville, Ohio,
The cure is easier than the explanation. Our sources say you have a common prob-+ lem, but they don 7 know just what it is. One theory is that the gas goes stale sitting in the carb. Another is that the fuel in the bowl evaporates. The level drops and the jets don 7 have fuel, but the drop isn 7 enough to< open the float valve, or perhaps the float needle has static friction or something.
Anyway; if you drain the bowls before starting, then open the petcock and let a complete fresh charge flow into the carbs, the engine will fire right up.
Too much bother and mess? If you know the bike will be parkedfor a week, then shut off the fuel a few blocks from home. Park the t bike with dry carbs and then when you get ready to ride next time, open the petcock and you'll have a fresh bowl of gas.
continued on page 88
continued from page 86
THE SQUEAKY SEAL GETS THE GREASE
I ride a 1974 BMW R90/6 with 24,000 miles on it. Recently I noticed an ungodh* squeaking noise coming from the engine., It sounded like a bearing going out or a dry bearing. I took it to the dealer and he said it was the crankcase ventilation valve. He pulled the right side oft' the air cleaner and1 put his finger on the end of the hose. This stopped the noise. The engine only does* this when it’s warmed up and only at idle. I imagine it doesn’t hurt anything but it’s annoying. Is there anything I can do to alleviate this problem?
Stephan Newberry^ Spencer, Okla.
BM W’s boxer motor runs with the crank** case at a slight vacuum. The squeak comes from the rear main seal going dry, or from a disc on the crankcase ventilation valve, which hops up and down under pull of the crankcase’s negative pressure. A
If you’re lucky, it’s the disc. You can remove it and lap the disc to its seat, just asyou do with a valve, and with valve lapping compound.
If it ’s the rear seal, you can cure the noise by oiling the seal. Thing is, getting to the seal requires removal of the transmission,^ etc. Because the crankcase has vacuum, the dry seal won ’t cause an oil leak, so if you don’t want the work, you can live with the squeak.
INTERLOCK SUGGESTION
I read the article on the long-term KZ1000 evaluation. You noted the annoyance of having to hold in the clutch while starting the bike. I noticed this too. I immediately began looking for and found a way to rid my bike of this little starting hassle. I have since applied this fix to several friends’ 1000s and 650 Kawasakis and to my Zl-R.
continued on page 94
continued from page 88
The fix is very simple and costs nothing. First, remove the gas tank and trace the wire from the clutch interlock swatch to the main wiring harness where you will find two plug-in connectors. Pull both of these apart. One wire in the main harness goes to the starter switch and the other to the starter. Simply cut the connector from one of these wares and replace it with one which will mate with the other wire. Plug these two wires together and you will have a direct circuit from the starter button to the starter and will no longer have to hold in the clutch while starting your bike.
Paul Hudspeth
Rontoul, 111.
BIGGER TIRE NEEDED?
I own a 1977 Yamaha XS750D. I am making a tourer out of it with a Vetter fairing and will also add bags and maybe a trunk. Could you advise me on whether it is a good idea to use a larger rear tire to increase safe load capacity? For example, a 130/90-16 rear tire. Also suggestions on a front tire would be welcome.
Michael R. Shelton
Clinton, Maryland
Forget about the 16-in. rear tire on your 750 Yamaha. It just won’t fit. There’s only a quarter inch of clearance between the 4.0018 rear tire now on your bike and the left side of the swing arm which houses the drive shaft. That’s why Yamaha’s 750 Special doesn ’t have the same large rear tire the other Yamaha Specials have. If you will be using the Yamaha solo most of the time, the stock tires are quite capable of handling the load. Even with two normal size people, the tires won't be overloaded unless you plan on taking the full-dress 750 on a rock hunting expedition. If you check around, you'll find that some 4.00-18 tires have higher load capacities than other 4.00-18 tires, so if you need greater capacity, choose a stronger; rather than larger tire. A Iso make sure you keep air pressure up when you ’ll be carrying heavy loads. The maximum load, by the way, is calculated for the tire operating at its maximum rated speed. If you have a V-rated tire, for instance, it has a greater load capacity at normal U.S. cruising speed than it does at its maximum rated speed. As far as the front tire goes, the stock 3.25-18 has ample load capacity for normal touring and it’s the size tire that works with the stock rear tire for the best handling on the motorcycle. 0
