Motorcycle Classics Blogs >

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

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

Blaster logo

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.

 

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

.

Blaster logo

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.

Blaster logo

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.