Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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Keith Fellenstein

Shifting issues

Q: I own a Norton Atlas with a single carburetor and magneto ignition. Lately, when I shift from first gear to second, it goes into second and then as I open the throttle it jumps into neutral. When I press down on the shift lever again it will go into second gear. I should also mention that I am having some clutch issues. The lever pull is very hard and the gearbox is a bit loud when shifting gears. What should I check first? — Mike LeBlanc/Moncton, New Brunswick, Canada

A: My first guess would be worn gear dogs causing your bike to jump out of second gear, but if it stays put when you push down on the lever it may be that the shift plunger that holds the gear cam in place is not doing its job. If it has been a few years since the gearbox has been renewed, now would be a good time to pull the guts out of the gearbox and inspect all the components for wear. Gear dogs get rounded off over time, bushings wear and mainshaft and countershaft bearings wear, too. The plunger that holds the shift quadrant in place gets rounded off and doesn’t provide a positive lock between gears. Bringing the gearbox back to specifications should give you more precise and steady gear changes. MC


Keith Fellenstein

Stuck bolt

Q: I have a frozen button-head Allen bolt with the socket stripped out. Can I use an extractor to try and remove it? — Curt Shontz/via email

A: I don’t like to use bolt extractors except as a last resort. There’s nothing more frustrating than having one of them break off while trying to extract a bolt, and since they’re harder than a drill bit they’re impossible to drill out. My favorite technique is to use a left-hand twist drill bit in a cordless drill set to reverse. Often the drilling heat will help extract the bolt. If it doesn’t, at least once you have the head drilled out and the pieces apart you can grab the stub of the bolt with vise grips and get it out. MC


Keith Fellenstein

Wiring search

Q: Where can I find the same colored wire on my 1974 Triumph Trident without buying a whole harness? I’m looking for small spools. Also, why do I have 6-volt coils with my Boyer ignition and a 12-volt battery? — Mike Stroobants, via email

A: You can find the individual wires you need to match your harness at British Wiring. They have complete harnesses and also the individual wires in a variety of color combinations, sold by the meter. The reason you have two 6-volt coils in your ignition is the Boyer is a wasted spark ignition; it fires both coils every time one of them needs a spark. One of the cylinders will be on the compression stroke and the other will be on the exhaust stroke. That means the coils have to be in series electrically, so two 6-volt coils present the same electrical load as one 12-volt coil would in a points-fired ignition. In a points-fired ignition, each coil is wired to a set of points and each coil is charged and discharged singly, so the electrical load flips back and forth between coils as the engine runs. Another way to do this would be with a single 12-volt coil with two spark outputs. MC


Keith Fellenstein

Energy transfer conversion

Q: I would like to convert my BSA C15S with the energy transfer system to a 12-volt battery/coil system, but I have no idea how to accomplish the task. Can you help me? — Bruce Riecke/via email

A: To begin, you will need a 12-volt stator. It also wouldn’t hurt to buy a new rotor, as they lose magnetism over time and won’t create as much current. You’ll also need to replace every bulb on your bike with a 12-volt equivalent. You’ll need to replace the energy transfer (ET) coils with conventional 12-volt units. If your ET coils are original equipment and in good shape, keep them someplace safe, as they are worth their weight in gold. You will need a 12-volt battery and a 12-volt rectifier, or you can use a Boyer Powerbox and continue to run without a battery. You will also need to find a 12-degree auto advance unit to replace the 6-degree ET unit. When I got my 1964 Triumph T100SC with ET ignition years ago, I wanted to upgrade to a 12-volt battery/coil but was advised against it by an old flat track racer who lives in my area. His advice was classic. “Does it work now,” he asked? “Yes,” I replied. “Then don’t mess with it.” I’m still running my ET. MC


Keith Fellenstein

GL guidance

Q: I have a 1981 Honda GL500 with 61,225 miles. The bike starts and runs well up to about 4,500rpm, then breaks up and runs really rough above that. It behaves the same way hot or cold. I’ve tried running it on the center stand with the same result. In terms of problem-solving, so far I’ve replaced the air and fuel filters and spark plugs, and I’ve cleaned the carburetors. None of this solved the problem. I then went on a CX500/GL500 forum where a member suggested replacing the plug wires and coils, which I changed, but this didn’t solve the problem either. I then located your article on CDI units and their function, and it seemed like the logical solution since I’m losing high-end. After changing both to a set ostensibly from a low-mileage bike, it still didn’t solve the problem. I also did a resistance check on the pickups (yellow and blue wires), with an accurate resistance reading on both sides. Additionally, I did the confirmation spark-check with the pick-up wiring harness disconnected. I find myself in a quandary wondering which way to look next and would like to ask for your help. Any suggestions? — Phil Quattrone/Pittsburgh, Pennsylvania

A: You’ve been very thorough in your pursuit of this problem from an electrical standpoint, to the point where I have to wonder if it isn’t a fuel delivery problem. The carburetors on the GL500s can be difficult to clean thoroughly, as the slow jet is pressed in on some models and difficult to clean properly. I once went through a pair of GL500 carbs three times before they began to work decently, and even then the owner claimed they improved over time with fresh gas and SeaFoam. I would consider cleaning the carbs again and, if possible, finding a shop that can run your carburetors through an ultrasonic cleaner. MC


Keith Fellenstein

Popping exhaust

Q: I just bought a 1969 B44 BSA 441 Shooting Star. My initial ride on the bike was fine, but I was getting just a bit of a pop out of the exhaust when I roll off the throttle. I ran it for a while, hauled it home, and then took it for another ride. This time it started popping a lot every time the throttle was shut. This is my first British bike (except for an AJS Stormer motocross bike I rode in the ‘70s), so I have no experience with them. Before I start fiddling about, I figured I should ask an expert. Does this sound like a timing problem? Or do I have fueling issues? The bike appears to be completely stock. It’s using an Amal carb, and the bike has about 9,000 miles on it. — Rod Jackson/via email

A: Popping on the overrun could be due to a too lean idle mixture from the carburetor. You can test this by turning the idle mixture screw in one-quarter to one-half a turn to richen the mixture. You may have to adjust the throttle speed screw to get your steady idle back. Then go for a ride and see if things are better. Another possibility is an exhaust leak at the head to exhaust pipe junction. Air sucked in there will cause popping in the tailpipe, too. MC


Keith Fellenstein

Tune up

Q: I figured it was time to do a tune-up on my 1970 Yamaha XS650. I had a tune-up kit a friend gave me, purchased in 1981 at Seattle Yamaha, and the “How-To” article from the January/February 2011 Motorcycle Classics  in hand, proper tools and experience. I timed the right cylinder, lining up the “F” on the engine cover with the timing mark and tightened down the backing plate. When I went to time the left-hand cylinder, the timing mark was advanced (to the left of) the “F” and there was not enough movement in the half-plate to bring it back (it was up against the stops/screws). I left it with the right-hand cylinder properly timed on the “F” and the left, slightly advanced. Do you have any suggestions on how to correct the timing of the left cylinder? — Terry Zeri/Bellingham, Washington

A: There are a couple of ways you can pull the left cylinder into correct timing. You can go back to the right cylinder and close the points gap by a thousandth or two. That will have the effect of advancing the timing for that cylinder. Then you rotate the full plate to retard the timing enough to bring the right cylinder back to the correct setting. That may be enough to allow you to use the half plate to correct the left cylinder timing. If that doesn’t quite get it, you can then open the points gap on the left cylinder by a thousandth or two, which will have the effect of retarding the spark for that cylinder. If the left cylinder is not too far advanced you may just be able to open the gap as mentioned and have that correct the timing. Good luck! MC

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