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

Yamaha XS650 Hard to Kickstart

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.

Hard to kickstart

Q: I have a 1975 Yamaha XS650 twin. It has had a tuneup and runs great. My problem comes when I want to start it with the kickstarter. Warm, cold or hot, it does not matter. There’s no way it will start. All I have to do is touch the starter button and it will start immediately. The coils are still original. Are they my problem? — Mike Trunk/via email

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A: I’ve had this question numerous times the other way around, where a bike will have a bad electric starter, but will start fine when kicked, but I’ve not seen one that won’t kick but will start on the button. My first thought is that kicking it may not be spinning it fast enough, especially if the compression is starting to fall off. Maybe the valve clearances are too tight and are letting the air out, so to speak. I had a look at the wiring diagram, thinking there might be a reason to be found there, but it’s pretty straightforward in 1975. Since it will start on the button, it’s not likely an electrical problem. I’d check the compression cold and hot, and compare it to spec. If it’s too far below spec, do a leak-down test to see where the compression is going, through the rings or valves, or even a blown head gasket.

Triumph T160 Trident 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.

Trident troubles

Q: I am approaching 95 percent completion in restoring my 1975 Triumph T160 Trident, and I have encountered a unique problem. With valves set, timing correct and all three Amal carbs synched, I drive slowly and she runs great. When I push her harder, as soon as I hit third gear she dies completely and every time I coast to the roadside. Initially, I was suspect of my Tri-Spark ignition failing. But I wait one minute and she restarts. As I ride her home and shut her down inside my silent garage, my freshly sealed and painted stock fuel tank is “whistling,” equalizing a partial vacuum. Did my new 5/16-inch clear plastic fuel filters excessively restrict my gravity fuel flow? Does my new chrome OEM fuel tank cap require a vent hole? Or should I mount my aquarium air pump on my dashboard and plumb it to my fuel tank for a “positive pressure” fuel flow? What did the OEM college boys design to relieve the fuel tank vacuum? I simply cannot believe our 91 octane is so poor that the 750cc mill is consuming fuel at a rate the lines cannot keep adequately supplied. I have drilled both tank cap holes to 1/16 inch and still — same vacuum. Should I drill both holes to 1/8 inch and set the float levels higher? Have you ever heard of such a unique malady? — Yukon John/via email

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A: Does it go completely dead? No coughing or stumbling first? That would point to an electrical problem. But your “whistling” tank points in another direction entirely, as you know. Since you mention it’s a newly painted tank, before you try this next test you should drain out about half the gas so you don’t slop out wholesale amounts of gas on your new paint. While you’re doing that it would be a good idea to measure the flow out of the taps to be sure they are flowing enough gas to keep the carbs full. I’ve not had to do this myself, but some quick searching indicates you should get close to 300ml per minute. Once you’ve done that, loosen but don’t remove the gas cap and go for another ride. The owners’ manual suggests that for sustained high speed running you should have both taps open, so if you’ve been doing that, continue. If not, try the loose cap with just one tap open and see if it improves, and again with both open to see if that is any better.

Honda CT70 Alternator Woes

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.

Alternator woes

Q: I have a 1970 Honda CT70 HK0 model (this is a 4-speed manual clutch model and different than the CT70K0 3-speed automatic clutch model). I need to rebuild the Mitsubishi alternator/stator assembly. The Honda schematic is unclear as to which lighting coil goes with the Mitsubishi assembly. I currently have the primary coil, points and condenser for this rebuild. Again I only need the Honda part number for the Mitsubishi lighting coil so I can try and track one down. — Tim/Colorado

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A: My usual go-to site for parts numbers doesn’t list numbers for items that are no longer available, so I tried cmsnl.com. There, they list the lighting coil as 03114098741. There are several entries for that item. Most show that it’s no longer available, but one shows they have three left. It could be a quirk of the website database, but may be worth pursuing. Another place to look if you don’t mind a little experimenting would be treatland.tv. They specialize in mopeds, and have lighting coils that might be adapted to work with your CT70. If you currently have a coil but it just doesn’t work, maybe an auto electric shop that rewinds starters and generators would be able to rewind your coil.

Trickle Charger Question

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.

Trickle charger

Q: I have recently obtained a 1970 BSA A65T Thunderbolt with a 12-volt positive ground system. I would like to keep a trickle charger on it if possible. No fancy lithium batteries here, just a plain old sealed unit. The gentleman who owned it previously had a pigtail connected to the battery for a trickle charger. He explained that the positive connection on the charger went to the grounded, positive side of the battery, while the negative side went to the, well, negative side of the battery, which is not grounded. When I connect my Battery Tender to it, the indicator light says that the charger is incorrectly connected and so it won’t charge. How can I correct this situation? If it matters, I have a Boyer ignition system. — Doug Stobbs/via email

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A: Check to make sure you really have positive from the charger going to positive at the battery. I suspect it’s not. Most charger pigtails have a fuse in the positive/hot line as most vehicles are negative ground. This will confirm which is the positive line. Even though your BSA is positive ground, the fused or positive lead from the charger should still go to the positive side of the battery. In other words, ignore the fact you have a positive ground system. My unsolicited advice is to not leave the tender connected all the time, just connect it as needed, say once a week or month, and remove it once it shows the battery is fully charged.

Lithium Batteries and Chargers

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.

Lithium batteries and chargers

Q: In your January/February 2017 column you mention that lithium batteries last longer maintained by special lithium chargers. Why? If special chargers are needed, maybe lithium batteries are not viable in our bikes with their non-specialized charging systems? And what is the life expectancy of the lithium battery? — Cliff Elkins/via email

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A: The chargers are designed to meet the requirements of lithium batteries. A single lead-acid cell develops higher resistance as it charges, while a lithium cell develops lower resistance as it charges. Lead-acid batteries self balance as each cell reaches capacity, while lithium batteries trend toward short circuit. A battery management system reads the individual cell charge state and directs charging voltage to the cells at a lower charge state. If your charging system produces between 14 and 15 volts at running rpms and if your battery has a built-in management system, a lithium battery should be fine. Battery chargers that have de-sulphation circuits should never be used with lithium batteries. Modern lead-acid battery chargers can be used, but should be monitored and disconnected once they indicate the battery is charged. Shorai says that their batteries have the same charging requirements as AGM batteries, but recommend their charger for the reasons laid out above. Shorai warrants their batteries for 5 years.

1966 Triumph TT Ignition

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.

 

Triumph ignition

Q: I have a 1966 Triumph TT with an ET ignition system. I have a five-wire stator and the armature has three holes in the back; S, M and R. Which one is the best for timing for street use and ease to start? How do I install the five-wire stator? It seems to me the end connections must be removed to get the wire through the opening in the tube. I am thinking the tube would be slipped on, then the ends soldered on. — Andy/via email

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A: The first part of your question is easy; the hole next to the S mark should be used to pin the rotor to the crankshaft for best timing for everyday use. The other two are for racing and will make it hard to start while giving better spark at high rpm. On the wires from the stator, you can remove the bullet connectors, but I’ve had good luck feeding the wires through one at a time. If the insulation has stiffened with time, careful use of a heat gun can soften the wires to make them flexible.

Finding Spark on a 1980 Suzuki GS850

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.

Finding spark

Q: I’m having trouble getting spark at the plugs on my 1980 Suzuki GS850. At first I wasn’t getting any spark, so I replaced the igniter unit. It then had spark, but when I installed the carburetors and tried again, there was no spark. What should I do? — Tyler Hubenthal/via email

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A: We’ll consider the igniter a good part. Get your volt-ohm meter (VOM) and check from the battery to the igniter for voltage. From the battery, there should be two wires: one to the starter relay and a second, smaller lead to the fuse box. Follow the smaller lead to the first junction, disconnect and test for 12 volts from the battery. If good, reconnect and follow that lead to the fuse box. Test the 15-amp circuit on both sides of the fuse for 12 volts. That leads to a multi-pin connector that leads to the ignition switch. If I can trust the colors on the wiring diagram I have, the 12-volt lead into the switch is red, out is orange. Orange leads back to the fuse box where it branches to feed three 10-amp circuits. The one we’re interested in looks to me like orange/white. Test both sides of the fuse for 12 volts with the ignition switch on. Next is the emergency stop, or kill switch. Test for 12 volts on the orange/white wire leading in and out of the switch. Now check the orange/white leads at the coils for 12 volts with the ignition switch on. Now we end up at the igniter. Test the orange/white lead there for 12 volts with the ignition switch on. Assuming you find 12 volts or slightly less at each of these test points, switch ranges on the VOM and test the signal generator that triggers the igniter module. You’ll find the connector under the left side cover. Put the VOM in resistance testing mode, set to 100-ohm range if not auto ranging and put one probe on the blue lead and the other on the green lead after disconnecting them from the igniter module. Look for a reading of between 250-350 ohms. If very low (0) or higher than 350, the signal generator is bad and needs to be replaced. Finally, pull number 1 and 2 spark plugs and rest them, connected to their high-voltage leads, on the cylinder to ground them. Set your VOM in resistance test mode to the 1 ohm range. With the ignition switch on, touch the plus probe to the blue lead, and the minus probe to the green lead on the harness side of the interconnect for the igniter. Number 1 should spark when you connect the second lead, and number 2 should spark when you disconnect it.