Motorcycle Classics Blogs >

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

Honda CL350 Gearing

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.

Honda gearing

Q: I have a 1973 Honda CL350 that I turned into a sort of bobber/café racer. It presently has a 36-tooth rear sprocket and a 16-tooth countershaft sprocket. At 70mph it is turning over 7,000rpm which is not far from redline. I’d like to get the gearing so I turn fewer revs at speed, but I don’t really know what would be best and I have limited funds. I’d like your opinion as to whether to go to a 35-tooth rear sprocket or a 17-tooth countershaft sprocket to lower the revs yet still give me good acceleration. Sprockets are limited for the CL350 and somewhat expensive for my limited budget. — Skip Baldwin/Picayune, Mississippi

 Blaster logo

A: The easiest way to drop the rpms is going to be to change the countershaft sprocket from a 16- to 17-tooth sprocket. As for expense, I found one at BikeBandit for $16 under Aftermarket Parts, Wheels & Final Drive. Of course, raising the gearing is going to slow the acceleration somewhat. There’s nothing you can do about that.

Triumph T150V Positively Grounded

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.

Q: I just read your Triumph Bonneville wiring advice in the March/April 2017 issue regarding a 1979 Bonneville ignition problem where you mentioned “ground the negative lead of the VOM to frame ground.” I have a 1973 Triumph T150V which is positive ground, and I believe all earlier Triumphs were positive ground as well. I do a fair amount of wrenching on old bikes, and it might be helpful for me to know: At what point in time did Triumph switch to the more conventional negative ground? Thanks for the great column. I read Motorcycle Classics from cover to cover, and your column is like the dessert following a fine dinner! — Dave Dawes/via email

Blaster logo

A: Looking through the workshop manuals I see the change happening with the 1979 models. They got a new alternator that year also, the RM24, and electronic ignition, the Lucas Rita. It’s not uncommon to find older Triumphs that have been converted to negative ground. It’s not difficult for a bike running points, and it makes it easier these days if you want to use modern LED lighting. Thanks for the kind words. I enjoy writing this column.

Triumph Bonneville Electrical 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.

Electrical woes

Q: I have a 1976 Triumph Bonneville that I built into a bobber. The bike ran great before I stripped it down and rebuilt it. I ran my own simplified electrical wiring harness. It already had the electronic ignition system installed. I didn’t touch the engine. Now I do not get spark when I kick it over. The battery shows 13.5 volts, the resistance is good on both coils, and I have checked all the wiring for continuity and correct connection. When I turn the key on and off, I get spark at both plugs. I also installed a new key ignition switch. What’s wrong? — Perry/via email

 Blaster logo

A: The quick and simple answer is that something is wrong with the wiring from the pickup coils in the points case. The black box is fine since you get spark when you turn it on and off. Remove the leads from the pickup coils in the points cavity and with the ignition on, touch the wire ends together momentarily. You should get a spark at the plugs when doing this. If you don’t, you have a problem with the wiring between there and the black box. If you do get spark that way, the problem is with the pickup coils.

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

 Blaster logo

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

 Blaster logo

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

 Blaster logo

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

Blaster logo

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.