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Tech Corner
Technical Q and A for classic motorcycle maintenance and repair.

Motorcycle Battery Worries

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Battery worries

Q: I just went out to start my bike, turned the key and got no lights at all. I attached a battery charger and my USB port LED lights up, but I’ve still got nothing else lit. What should I check for? — Bob Gent/via email

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A: The first thing I’d check would be the charge level of the battery. Anything less than 12 volts and you definitely need to charge it. Next, I’d check the electrolyte level of the cells. If the electrolyte level is low or has been boiled off due to overcharging, the battery may show 12 volts, but have very little ability to push current, and current is what you need to make the incandescent bulbs in your bike light up. Your LED lights up because it requires milliamps of current where your incandescent bulbs require more. If you do find the electrolyte levels are low, go ahead and charge the battery. After it’s charged, add distilled water to each cell to bring them back to acceptable levels. If you do all this and still get no lights, have a look at the fuse box. MC

1979 Triumph Bonneville T140E Wiring

Motorcycle Classics tech expert Keith Fellenstein 

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Bonneville wiring

Q: I have recently acquired a pristine original 1979 Triumph Bonneville T140E 750. It has been in storage since 1981. I am having difficulty getting fire to the plugs. This bike has a Lucas pointless system and I haven’t been able to find a manual that provides info for this particular system. I’m relatively certain the ignition module is shot as there is no fire at the spark plug. There is power to the module. Without specific info concerning the Lucas components, I cannot be certain what to replace or not. So far, I haven’t found the “E” designation on any of the manuals I’ve researched. It’s my understanding that is the emission compliant version for the model years 1978 through 1983, hence the electronic ignition. –  Dale Lawless/via email

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A: Your T140E is indeed the emissions compliant version of the 750 twin. It would have the Lucas Rita electronic ignition, which has been out of production for many years. If it has failed you have a variety of options for replacement, including Sparx, Pazon, Boyer and Tri-Spark, to name a few. But before you replace the system, let’s run through a few tests to see if there’s a simple fix. We’ll start with the trigger, found in the cavity on the right side of the engine where the points would be on a standard ignition. You probably have the type used with the AB11 amplifier. Disconnect the leads to the trigger and using a volt ohmeter (VOM) set to read ohms, measure the resistance across the leads to the trigger. It should be in the range of 600 to 700 ohms. Reconnect the trigger. Next, remove a plug or attach a spare spark plug to one of the high tension leads. Lay the plug on the cylinder head. Turn the ignition key on and off, this should produce a spark at the plug. Next, check for voltage at the left coil by switching the volt ohmmeter to DC volts. Place the positive probe on the positive terminal of the left coil, and ground the negative lead of the VOM to frame ground. With the key on, you should read 12 volts on the VOM. Move the positive lead to the negative terminal of the left coil and check the VOM again. Your voltage will drop slightly as you move from coil to coil, but an abrupt drop to 0 will indicate a bad coil. Move to the positive terminal of the right coil and check the VOM. This and the last reading from the negative terminal of the left coil should be the same as the coils are connected in series, with the negative of the left and the positive of the right directly connected. Move the positive lead to the right coil negative terminal for the last of this test and again check the VOM. Since the coils are connected in series, a failure in one coil will bring the whole circuit down. Finally, switch the ignition off, set the VOM to ohms and check the resistance from the right negative terminal to ground. It should read 0 ohms if the wiring is good. If none of these tests show the fault, the amplifier is probably bad and you’ll have to buy a new electronic ignition. Finally, disconnect the black/white and black/yellow leads that come from the amplifier to the coils and with the VOM set to DC volts, test each lead to ground. If both read 12 volts, the amplifier is bad. MC

1968 BSA 441 Victor Stuck on a Whitworth

Motorcycle Classics tech expert Keith Fellenstein 

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Stuck on a Whitworth

Q: My 1968 BSA 441 Victor has a nut that I can’t manage to remove. It’s the one down inside the fuel tank that secures the tank to the frame. The nut is rounded off. This seems like an impossible place to reach with my limited collection of tools. Any suggestions? – John Grenier/via email    

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A: I’ve run into this problem before, and at the time I had to carefully force a socket over the nut and then carefully unscrew it. An easier way would be to get a set of bolt extractors. These are specially machined sockets made to fit over a rounded bolt head and bite into it so it can be unscrewed. Individually they can be expensive, but you can buy an inexpensive set from BikeMaster.

1968 Triumph T100S Fork Oil Questions

Motorcycle Classics tech expert Keith Fellenstein 

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Fork oil questions

Q: I have a 1968 Triumph T100S and want to change the fork oil. I have taken the drain plugs out of the bottom of the fork legs and will let the oil drain for a day or so. For refilling, I have a few questions: I assume I take the nuts off at the top of the triple tree. My manual says to add 190cc to each leg. Do I just pour the oil in the top and replace the nut? What oil do you recommend to use? I have Harley-Davidson fork oil from my old Shovelhead days left over, would that be OK? Some people have advised to use ATF transmission fluid, but I don’t want to mess this up. John Schaub/via email

A: In addition to pulling the plugs and letting the oil drain, it’s helpful to pump the forks to get even more oil out. Unfortunately, with the drain holes pointing left and right, pumping the forks just about guarantees spraying oil all over the place. Once you’ve emptied the forks as much as possible, you do indeed just pour the oil in the top. You should either put a jack under the engine to support the bike while you remove both caps, or take the easy way out and just remove and replace one at a time. Either way you’ll have to compress the spring to get the cap back on the fork tube. That’s easiest if the bike is jacked up so the least amount of load is on the fork springs. Take your time pouring the oil back into the fork tubes as the oil will collect in the spring before trickling down into the lower stanchion. Your Harley fork oil should be fine, too, providing it’s 20w fork oil. After 1972 Triumph recommended ATF for fork oil, probably because is was a similar weight and easy to source. MC

1981 Yamaha XS650 Stalling Problems

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Stalling 1981 Yamaha XS650

Q: I’ve been enjoying your magazine for a number of years now, but this is the first time I’ve needed to write for mechanical advice. I have an essentially stock 1981 Yamaha XS650 Special. Outside of some initial carburetor issues when I first bought it, the bike has performed flawlessly, until now. I try to put a few miles on it every week or so, and last week when I took it for a spin the engine inexplicably died about 7 miles into the ride. No stuttering, sputtering or misfires; it just quit as if I had inadvertently hit the kill switch. I tried to restart it, and although it turned over with both the electric and kickstarters, it wouldn’t catch. I checked the fuel lines, vented the gas tank and checked the plug wires, but that is about the extent of my roadside mechanical acumen. About 15 minutes later, as I was waiting for my distress call to be returned, I tried it again and it started right up. Hopping on I headed home, but it died again after about 4 miles. I waited another 15 minutes, it started up, and I made it home just as it died again, after about another 3 miles. I’ve taken it for a test drive around the neighborhood and the same thing happened again. Because the problem comes on so suddenly and affects both cylinders, I suspect the ignition coil (my understanding is that this bike has a single coil), but before I start randomly replacing parts, I thought I might seek a little guidance. Any insights into this problem would be greatly appreciated! Jan Cordes/Yorktown, Virginia

A: I think you’re right about the ignition coil, and my guess is that it’s heating up and opening up either the primary or secondary side. It’s also possible the pickup coil in the alternator has gone bad. You can test the pickup coil by first disconnecting the plug between the air boxes. The plug should have black/white, white/red and white/green wires. With an ohmmeter, measure the resistance between the black/white and white/red leads, and again with the black/white and white/green leads. In both cases the meter should read between 550 and 850 ohms. Ideally you’d test this as quickly as possible after a failure, since your failures seem to be heat related. If that tests out OK you can proceed to test the ignition coil, but you’ll have to remove the tank to do that. Probing the primary side of the coil (the side not connected to the plugs) should result in a reading just shy of 3 ohms. Checking the secondary or spark side your readings should be somewhere in the 10,000 to 20,000 ohm range, depending on condition of the resistor plug caps. If after all this testing you find those components are fine, the only thing left is the TCI unit, which can’t be tested by ordinary means. MC

1975 Norton Commando 850 Podtronics Unit

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Podtronics and RFI suppression

Q: Last summer I acquired a 1975 Norton Commando 850 MKIII that had been built by a friend. This is an award-winning bike and was well sorted. However, shortly after getting it, main fuses began blowing after putting the bike in gear starting out, I’d get a few inches before it stopped. After much analysis and investigation the builder decided it was the Podtronics unit which was at fault and replaced it at his cost. He then suggested I replace the spark plug covers with suppression ones, thinking this caused the unit to fail. I have successfully started and ridden it very short distances; so far so good. But the weather here has turned cold so it won’t likely get taken on a longer ride until spring. Does this solution sound right to you? I am, not surprisingly, concerned about going far and getting stranded. I know how to disconnect the Podtronics if that occurs, but would then have no charging of the battery so the ride home better not be too long!  Bruce Mitchell/via email

A: I’ve searched high and low and can’t find any indication that the Podtronics regulator/rectifier requires any RFI suppression to operate correctly. If you’re running an electronic ignition system, they usually require RFI suppression in the form of resistor plugs or resistor caps. If you have one you generally don’t need the other. You don’t mention whether your Podtronics is the model with the built-in capacitor for battery elimination. If you had that one and the capacitor had gone bad I could see a situation where it would short out and blow your fuse. I guess it could be possible that your neutral indicator light was shorting out and blowing the fuse, but that would have been a continuing problem that carried over to the new Podtronics. I think you just got a rare bad unit. MC

1974 Honda CB550 Carburetor Issues

Motorcycle Classics tech expert Keith Fellenstein

Editor’s note: If you’re having trouble with that old Suzuki, BSA or BMW, Keith Fellenstein is your guy. From motorcycle tuning tips to detailed motorcycle engine repair, he can draw from a wealth of experience to help guide you to success. Send questions to: Keith’s Garage, Motorcycle Classics, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as the subject.

Carburetor issues

Q: I rebuilt the carbs on my 1974 Honda CB550, and the bike runs better except for one new problem: When the bike has run for about 10 miles, it will idle too fast, about 2,000rpm, for a while. At a long signal, it will settle back down to the correct idle, or if I let out the clutch a bit to slow the motor down, it will stay slow. I thought it might be a problematic spark advance, so I replaced the points with a Boyer electronic ignition (which controls the advance with software), but the problem remains. I have sprayed water on the intake manifolds to check for an intake leak, but found nothing. The throttle stops and mixture screws were set on the bench, and not dialed in with a vacuum gauge. Any thoughts? This is a real problem, as I am not getting the normal engine braking. I also installed a lithium ion battery, which came without charging instructions. Can this be charged with a trickle charger? Tom Hund/via email

A: I’ll start with the easy answer first. Regarding the trickle charger, no. Most lithium batteries will last much longer if you use a charger made for them. As for your runaway idle, most of the time that is caused by an air leak bypassing the metering system of the carburetor, but you’ve tested for that. Have you tried spraying carb cleaner instead of water? That might show more minor air leaks than water. You should probably pull the tops off the carburetors and make sure the slides are all dropping the same distance at the same time. A set of vacuum gauges would tell you immediately if one or more of the carburetors was playing up. MC