Tech Corner

Technical Q and A for classic motorcycle maintenance and repair.

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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


Keith Fellenstein

Losing spark

Q: I have a 1980 Honda CX500C. It starts easily and runs great until it gets warm. Once warm, it loses spark on one cylinder. Any suggestions as to what is wrong with my bike? — Mitchell Smith/via email

A: It is likely you have a bad coil that is opening up when it gets warm. You could try switching the coils from one side to the other and see if the problem follows the coil. If it does, you can bet the problem is with the coil. MC


Keith Fellenstein

Blown clutch

Q: I blew the clutch on my 1975 Kawasaki H1 500. It had been bad for a while. When it finally went, I couldn’t downshift and the engine lost power and died. I finally got it back into neutral and tried to restart it. There is now very little resistance felt in the kick-starter, but it doesn’t feel like it’s broken. I drained the oil and it had plenty, but it was black and smelled like burnt clutch. I pulled the spark plugs and the pistons don’t move when I kick the engine over. Could this possibly just be a blown clutch or do I have more serious problems? — Clark Connelly/via email

A: If the clutch had been getting progressively worse I would assume it finally failed. It’s unusual for one to fail so spectacularly that you can’t turn the engine over with the spark plugs removed, but I guess it’s possible. I think your next step should be to remove the clutch side cover and disassemble the clutch. If it isn’t grabbing at all the wear on the friction plates should be quite obvious. The steel plates might still be good unless they have been overheated and blued from clutch slippage. If you’re going in to inspect the friction plates, it’s probably a good idea to just replace them. They’re not that expensive and since you’re in there anyway you may as well renew them. Let us know what you find. MC


Keith Fellenstein

Triumph stumble

Q: I have a 1965 Triumph Bonneville T120 with 1,000 miles on it since it was rebuilt. This engine ran fine for approximately 600 miles, but then began to stumble and lose power after about six miles of riding. When I stop for a minute or two, it will start and run again, but only for a half mile, then it stumbles and loses power again. It will not generally get above 20mph once it begins to act up, but it does stay running. It will stall once at idle. It is running one Amal carburetor with a Pazon ignition. The battery is charging 12.7-13.2 volts (approx.). I replaced the coil. It ran strong for about 200 miles after that, but then started the symptoms all over again. The plugs are evenly colored with no carbon build up to speak of, nor any indication of running lean. Popular opinion is there is an overheating problem affecting ignition performance. It acts as if it is being starved of fuel, but there appears to be no reason to suspect the carburetor. I have good fuel flow from the tank. I even checked the cap to ensure that the venting wasn’t plugged. Thanks for any assistance you can offer. I’m stuck. — Jonathan P. Young/Fort Drum, New York

A: It could be a compression issue. Since the problem started soon after a rebuild, I have to ask if you’ve retorqued the head bolts. Depending on the type of head gasket used, you may have to do this a few times. You can check for low compression with a compression tester or a leak down tester. Another possibility is overheating of the electronic ignition trigger in the points cavity. You can quickly rule this out by pulling off the points cover and going back out for a ride. That will keep the trigger assembly cool. If the problem disappears you’ll know to replace the trigger assembly. Or it could be a problem with valve clearances; everything runs OK until the engine warms up and valve clearances start to close up. Once that happens your valves won’t seat as they should, leaking compression and causing the engine to lose power. Double check your cold valve clearances. They should be 0.002 inches for intake and 0.004 inches for exhaust. As a test, if they check out OK you could add 0.001-0.002 inches to each setting and see if that makes a difference. If it does, then you know there is a problem with the valves. If it’s a problem with the head gasket, you’ll probably have to pull the head and replace it if it’s composite, or reanneal it if it’s copper. Then be sure to do the retorquing to keep it sealed. Good luck. MC

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