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

Triumph T120 Tiger Spark 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.

Q: I have restored my 1971 Triumph TR6R T120 Tiger from top to bottom. The engine and electrics were professionally done, while I stuck to the other things. I’ve had the bike out half a dozen times and all seemed fine. Recently, while riding my Tiger, which now has 168 miles on it after the rebuild, my engine decided to run on one cylinder. I limped home. The coils are original Lucas 17M12. I checked for spark at the plugs first, the wires secondly, and got spark on the left side (as I sit on the bike) but not the right side. The bike has a new Pazon ignition in it. I then switched the wires to the opposite, and also did the same with the plugs and the coils. I got the same results on the right side — no spark. I took an ohm reading on both of the coils and got 4.7 on the primary side, and 5.36 and 5.3 on the secondary sides. I also changed gas. Upon start-up after all of this, the bike ran fine for about 30 seconds and then the right cylinder stopped running again. Am I on the right track to assume that I need to replace the coils? Both sparks are orange/light yellow when they fire. Are the coil ohm readings correct/within specifications, or does it indicate that they need to be replaced? The book says 3 ohms minimum and 3-4 ohms maximum for primary resistance, but nothing about the secondary resistance. Maybe I’ve answered my own question, but I’d like to hear from an expert if I am on the right track. — Burt Horner/via email

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A: The biggest problem I can see is you are running two 12-volt coils in series in a wasted spark ignition system that calls for two 6-volt coils in series. Since the Pazon charges and fires both coils every time, you are giving it too much of a load to deal with. Switch to two 6-volt coils in series or get one dual output coil of 3 ohm primary resistance and I think your problems will disappear. Update: I got an email back from Burt, and after changing to 6-volt coils and chasing down a grounding problem, he’s on the road again.

Intermittent Charging on a Yamaha XS750

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 have had an intermittent charging problem with my 1978 Yamaha XS750 Triple since the day I bought it. I bought it two years ago with 18,000 miles on it, and now it has 20,000. The previous owner installed a new regulator, so the first thing I did was install a new battery and repair the wire connections at the stator (it had been dropped and it pinched one of the wires). I use an amp meter on the battery side. When charging, it shows 5 amps at 2,000rpm with the lights on, which I think is a bit low, but according to the Yamaha manual I have is what it should be. But I find when I ride it the charging becomes intermittent and eventually drains the battery. As an experiment, I took it on a 75-mile round trip, with a friend in front of me, for safety reasons, and one following. It may be coincidental, but it seemed when I would hit a bump in the road it would sometimes alter the charging state. I have checked and rechecked all the connections and repaired a few of them to no avail. Would the headlight perhaps cause this, or do you have any suggestions?
Dennis/via email

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A: I think you found the obvious fault in the pinched wire, but perhaps there is some hidden damage in the stator windings that shorts out when jarred. You could try a used alternator from eBay, or go whole hog and get a rebuilt one from Rick’s Motorsport Electrics. The latter is more expensive, but you know you’ll get a good unit. If you’ve checked all the visible connections, that leaves the ones you can’t see on the inside of the case.

Honda CBX Master Cylinder Repair

Keith's Garage

 

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’m working on a restoration and need to repair the master cylinder on this bike. The problem is the bike has been sitting since 2002, and the brake fluid is likely original. The bores are corroded and will probably not seal properly. Do you know anyone that can “bore” the plunger holes and fit an oversize plunger and seals? Any information will be helpful, thanks.
John Montes/via email

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A:   If you have the cylinder bored, you’ll want to have it sleeved back to the original size. Increasing the bore size of the master cylinder will reduce the effectiveness of the hydraulic brake. There are sleeve kits available for several British bikes that reduce the bore size to increase the braking, but I don’t know of any companies offering this service for Hondas.

 

Suzuki T20 Charging Issues

Keith's Garage

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:  My father and I are restoring a Suzuki T20. It’s all going great and we’ve had it running quite nicely. We have noticed that it isn’t charging the battery, though. We removed and checked the rectifier and that seems OK (resistance is only showing one way). We have had an ammeter in line with the battery and you can see the current draw as you turn on the ignition, then more as the lights come on, but when it’s running it doesn’t change. We have a Suzuki Hustler that’s been a temporary parts bike and removed the alternator off that to swap. With them both on the bench we tested the continuity of the coils and found the T20 only had one good pair to the Hustlers’ three! Thinking this was the fault we rebuilt the alternator. Now we can’t get it to run? The lights come on, but there appears to be no spark. We have checked and rechecked the connections, but wondered if you have any advice.

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A: The old Haynes manual I’m looking at says the alternator has six coils, wired up in pairs. With the headlight switch off, only one pair of coils is used, for ignition and the brake light. If you turn the headlight switch on, the other two pairs of coils are connected in parallel to the original two for added current capability. From this I’d check to make sure the coils are switched together correctly. If they’re joined in series instead of parallel the output will be different. Find a way to test one pair of coils isolated from the rest of the wiring harness by jumpers to the regulator to see if you get a spark.

 

Triumph Thunderbird 6T Fouling Plugs

Keith's Garage

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’m trying to find out if I have the correct carburetor and jets on my 650cc 1966 Triumph Thunderbird 6T. I’m having trouble with fouling plugs after a rebuild. Who can I contact, or can you help me? I have tried contacting Amal

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A: I looked through the manuals I have from Kim the CD Man and came up with two options. It looks like 1966 was the last year for the 6T. You should have the Amal Monobloc kitted out like this: 376 carburetor, 230 main jet, .106 needle jet, needle type C, clip in position #3, slide 376/4, pilot jet 25. Should you for some reason have an Amal Concentric, the setup is as follows: 930/23 carburetor, 230 main jet, .107 needle jet, standard needle, clip in position #2, slide #3. Hope this helps.

Trickle Charger Update

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 update

Several readers have written to address a glaring omission in my last column regarding trickle chargers and 12-volt positive-ground motorcycles. Specifically, the bare lead of the pigtail will be the hot lead and must be prevented at all times from contacting the frame or you will short the battery to ground with no fuse to stop you. I don’t know how I missed this, but thanks to everyone who wrote to point this out; it’s important.

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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

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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.