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


1970 Triumph T120 Fork Leg Thoughts

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 email with “Keith’s Garage” as the subject.

Fork leg thoughts

Q: I am putting my 1970 Triumph T120 fork legs back together after some work on them. I want to make sure that they don’t leak where the dust covers mate with the lower legs (at the threaded junction). A friend said any good silicone sealer would work. Do you think Permatex High-Temp RTV Silicone Gasket Maker would be appropriate? I just happen to have some in my shop. I guess the issue is whether that would make it too hard to undo them down the road? I enjoy your column. Keep the rubber side down.

Crocker Bennett/via email

A: I too would be concerned about disassembling them the next time. If you go this route I’d only smear a little on a few threads, not the entire threaded portion. I wonder if Anti-Seize would work? It’s a heavy grease. Kill two birds with one stone perhaps?

Positive or Negative Ground for 1973 Triumph TR7RV?

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 email with “Keith’s Garage” as the subject.

Positive or negative?

Q: How would I determine if my 1973 Triumph TR7RV is positive or negative ground? I assumed that it was positive ground, but I hooked it up that way and it blew the 30-amp inline fuse on the negative cable. I do not know a lot about these British bikes. Thanks.

G. Manning/via email

A: First off, use a 15-amp fuse, as the ratings are different between British and U.S. fuses and a 30-amp British fuse as called for in the rider manual is a 15-amp American fuse. Next, the fused negative cable goes on the negative post, the positive post (red wire usually) goes directly to ground. If it still blows fuses after these changes, there is something else wrong with it. All this advice assumes it’s got the standard plate rectifier and Zener diode voltage regulator. If it has an aftermarket regulator/rectifier combo it may be a little more difficult to troubleshoot. Let me know if this fixes the problem.

Positive or Negative Ground for 1973 Triumph TR7RV?

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 email with “Keith’s Garage” as the subject.

Q: How would I determine if my 1973 Triumph TR7RV is positive or negative ground? I assumed that it was positive ground, but I hooked it up that way and it blew the 30-amp inline fuse on the negative cable. I do not know a lot about these British bikes. Thanks.

G. Manning/via email

A: First off, use a 15-amp fuse, as the ratings are different between British and U.S. fuses and a 30-amp British fuse as called for in the rider manual is a 15-amp American fuse. Next, the fused negative cable goes on the negative post, the positive post (red wire usually) goes directly to ground. If it still blows fuses after these changes, there is something else wrong with it. All this advice assumes it’s got the standard plate rectifier and Zener diode voltage regulator. If it has an aftermarket regulator/rectifier combo it may be a little more difficult to troubleshoot. Let me know if this fixes the problem.

1976 Suzuki GT750A Cylinder Problem

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 email with “Keith’s Garage” as the subject.

Ignition or carburetion?

Q: I have a question about my restored 1976 Suzuki GT750A. I did a complete engine overhaul on the bike, split the cases and had the crank rebuilt, including new oil seals. The CV carbs were also rebuilt. It has happened twice now during a ride that all of a sudden I lose power on one cylinder completely. It runs on only two cylinders for a bit and while I can keep the engine going on two cylinders and play with the throttle a bit all of a sudden it kicks back in and operates like nothing happened. Could this be an ignition issue or carb issue?

Jerry Gooren, Hayden, Idaho

A: Since it’s always the same cylinder, and the easiest thing to check would be ignition, I’d start like this: Rewire the coil from the constantly bad cylinder to one of the others, and swap that cylinder’s coil to the bad one. See if the problem migrates to the newly assigned cylinder. If so, you have a bad coil. If the problem remains with the original bad cylinder, then you should check that cylinder’s carburetor and mountings.

1978 Kawasaki KZ650C Mikuni Mixture

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 email with “Keith’s Garage” as the subject.

 

Mikuni mixture

Q: I could use some help setting the mixture on my carburetors for my 1978 Kawasaki KZ650C. How many turns out on the air/fuel mixture screw do you go to adjust a Mikuni carb? Remember there are four carbs on this bike.

Brian Rhenlun/via email

A: It’s almost universal that idle mixture screws are set at 1.5 turns from gently closed. Start there and turn them all out 1/2 turn and see if the idle speeds up. If it does, go a further 1/2 and check again. If no improvement try a 1/2 turn in from your start position and do the same test. Once you have figured out the right direction, fine tune in 1/4 turn increments. Once you have the fastest idle, use the idle speed screw that controls all four carburetors at once to set the correct speed. After that you may need to go back and double check the mixture. It can take a while to get it just right.

1971 Triumph T150 Electric Start Conversion

Motorcycle Classics tech expert Keith Fellenstein
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 email with “Keith’s Garage” as the subject.

Triumph T150 electric start

Q: I was reading your article in a recent copy of Motorcycle Classics about converting a Triumph T150 to electric start. I have a 1971 T150 and would like to do the same. Can you provide me with more information as to where I can buy the components (kit form?) or who might do the conversion for me?

John Damon

A: It used to be easier to find the parts from the 1975 Trident needed to convert the earlier models to electric start. Then the idea became popular and now parts are scarce. You need the clutch basket from a T160, or a late model T150 clutch basket and the ring gear that goes on it. L.P. Williams in England has the ring gear if you have the clutch basket. I believe you can have earlier clutch baskets machined to take the ring gear, which is an interference fit on the basket.

Next you need the inner clutch cover from a T160. A quick search of eBay shows there are none currently available there. David Madigan is manufacturing a cover, but it is in the early stages and not for sale as far as I know.

Finally you need a starter motor and again David Madigan is the best source. Oh, one more thing I forgot, you need three of the early Amal concentric float bowls, the ones without the drain plug. They’re needed because the T150 engine doesn’t slope forward like the T160/R3 engine, so there’s no clearance between the starter and carburetors. You’ll have to search around the various British parts shops for those. I think I’d start by contacting David at the email address above. I hope this helps. I sure enjoy my Trident more with the electric foot.

Suzuki T20 Fiberglass Tank

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 email with “Keith’s Garage” as the subject.

Suzuki T20 GP kit

Q: I have a NOS GP kit temporarily set on one of my T20 projects, just to get a visual. It is two projects away from starting and I’d planned to Caswell coat the tank for ethanol protection. It will get ridden several times a year and taken to our Western VJMC rally. The tank will be drained when not ridden. My understanding is the Caswell product can be used to protect fiberglass tanks from our wonderful Cal-ethanol “gasoline.” I’ve used it successfully on a couple of needy steel tanks. You recommended that Joe M. replace his GP tank with a steel one, and if it was never coated, I would agree. My tank has never been used and appears very solid. Would you have any reservations about my plan? I can hardly wait to get the first, of three, T20s together with the GP kit and stainless Higgspeed pipes on the road.

Mike Corcoran/via email

A:If it’s a virgin tank, I’d have no reservations coating it in order to use it. Just go completely by the instructions. Being a bit paranoid, I’d probably see if there was enough in the kit to do two tanks, and do a double coat in case there were any voids in the first coat. The tunnel can be particularly hard to coat properly. Another problem area is the interface between the fiberglass and the metal bungs for the petcock taps. It will be difficult to get the perfect seal between the glass and metal. I’m not saying it can’t be done, but it could be a problem. A couple of people with Norton fiberglass tanks have gone to the extreme of cutting the bottom out and coating the parts, then reassembling to assure complete coverage.







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