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

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

1968 BSA A65 Head Gasket Troubles

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.

Head Gasket Troubles

Q: My 1968 BSA A65 is leaking oil at the head gasket. This leak has been going for quite a while, and before it gets really bad I want to take the head off and try to anneal the copper head gasket and hopefully reuse the gasket. My question is how best to do that with a propane torch? Should I dunk it in water immediately after it gets to dull orange to quench it, or should I lay it on a flat surface to air cool? What other things should I look at with the head off? Would it be a good time to lap the valve surfaces? And finally, what would you recommend for a copper sealant on the head gasket? — Peter A. Akerman/via email

A: You can find people who claim one way or the other is best, but they work equally well. The advantage to the quench method is that it usually shocks the oxidation scale off that you otherwise have to scrub off. I usually use a couple coats of Permatex Spray-A-Gasket before installing a copper head gasket. It’s always a good idea to check the valves when the head is off. If you don’t want to pull them apart to check guide wear and valve wear, you can at least check them for proper sealing. Turn the head over so the combustion chamber is up, then spray penetrating oil into the dome. Go away for a while and when you check back, look for evidence of oil seeping into the intake and exhaust ports. MC

1969 BSA 441 Electrical Upgrades

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. 

Electrical upgrades

Q: I have a 1969 BSA 441 Victor Special that I purchased out of the crate from England way back when. I have it stored in my hangar and I want to keep it pristine. It is hard to start. I replaced the battery when I purchased it with the battery replacement kit (a blue capacitor) since we rode a lot of mining roads in the mountains. If I were to replace the ignition what would I look for? Also, where can I purchase some decals? J.E.H. Knutson/Boulder, Colorado

A: If you’ve had the bike this long on the original capacitor, it’s long past time to replace it. Those capacitors dry out and lose the ability to store electricity, and sometimes fail with a bang, too. Timing is critical on those big singles. If you’re not spot on they can be hard to start or prone to kicking back. Make sure your points advance unit is working smoothly, as sometimes they can stick. It sounds to me like you don’t ride the bike every day, so including a battery in the mix is just going to be another source of frustration when it shows up dead just when you want to ride. I was at a meet awhile back where a similarly aged Victor started up easily. Here’s how it worked that day: Taps on, tickle the carb until the bowl flooded. Pull compression release and kick through three times. Turn the key on, pull compression release, kick with vigor and release the compression release. Walridge Motors and other Brit parts houses stock decals. MC

1967 Triumph Bonneville 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 have a 1967 Triumph Bonneville with 18,000 miles on it. It recently started running with a rough exhaust note once it was warm. After sitting all winter it started with one kick, but from then on it ran very rough. The left cylinder exhaust ran hot on start. The pipe and exhaust were hot while the right side was cool. I thought maybe I had a tight exhaust valve, so I adjusted it. It was better, but still not right, so I readjusted it, and the left cylinder went back to running hot. It still starts on the first kick. I have also noticed that the carburetor ticklers take forever to flow, where in the past they filled more quickly. – Peter/via email

A:  When you say the right pipe was cool it sounds like maybe the right cylinder wasn’t firing, or did you mean that in comparison to the left it was cooler? Assuming you meant the latter, and knowing that it sat all winter, I’d suspect a restricted/clogged jet on the left carburetor leading to a lean condition for that cylinder. Just to be sure of the state of the fuel system, I’d pull the carburetors and clean them both. Since you mention difficulty in getting the ticklers to work well, double check the float heights. They shouldn’t change on their own; they are difficult enough to change on purpose unless you are using the new StayUp floats. Another possibility if the bike is still on points would be timing differences, with the left cylinder running with the timing retarded in relation to the right cylinder, but since you said it ran well enough when parked I’d check the fuel delivery system first.