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, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject.  

1978 Triumph Bonneville Idle Jets 

Q: I am the original owner of a stock brown and gold 1978 Triumph Bonneville that was running great until last summer. I lost my idle. This had happened previously because of clogged idle jets. I took the bowls off and one was clogged, so I cleaned and replaced everything. The idle was better, but not perfect. I adjusted and got the idle right, but after a few minutes it would slowly die, as if it was running out of fuel. I figured I may still have some residue inside, so I put some fuel treatment in it. It started, but after two minutes while waiting for it to warm up, it lost power. It was running, but flat. Both cylinders were firing, but then it died. I have not been able to start it since, and it seems to have no spark. Fuel is present. I still have points, the original Zener diode and the rectifier. It has shown no signs of firing up since. - Bob Conrad/via email 

A: Several possibilities spring to mind. Let’s work our way through from easier to harder. Since you say there seems to be no spark, let’s start with the electrics. One of the easiest and least expensive tests is to just put in two new spark plugs. If that changes nothing then you’ll have to move on to more time consuming tests. You’ll want a multimeter, as they make electrical troubleshooting much easier. How’s your battery? If it’s more than a couple of years old, it’s probably time for a new one. If it has a good charge, then move a little farther down the circuit. Is the fuse good? Sometimes those old barrel fuses look fine but the end cap has become unsoldered from the fusible link. Once you get past the fuse, use your multimeter to test for 12 volts. Is there 12 volts at the ignition switch? If so, turn the switch on and continue to the coils. Is there 12 volts at least at one of the coils? Running points, one set could be open and that coil would have no voltage. If you find 12 volts at the coils, push the kill button a few times and make sure it always comes back to 12 volts. Those Lucas switches get corroded after all these years and can keep you from starting or running. Next, pull the points cover and check for voltage at the points. You can turn the key on and use a small screwdriver to open the set of points that are closed. You should see a small spark. If you have the spark plug for that cylinder out and the base of the plug grounded, it should spark at the same time. If you get no spark at the points go back to the last point where you had 12 volts and examine the wiring between there and the points, looking closely for loose junctions. That’s a good idea for this whole exercise; any time in these tests that you lose 12 volts, go over the wires from that point back to the last good 12 volt point, checking for loose connections. MC 

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, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject. 

1970 Triumph Bonneville 650 Heads 

Q:  I own a 1970 Triumph Bonneville 650 with the wrong head. The head on my bike right now is a 1971. Since it is very difficult to find a good 1970 head, do you think I can use a 1966-1968 head? What are the differences? - Lorenzo Tripaldi/via email 

A: I didn’t know the answer to this question, so I enlisted the help of a Triumph aficionado I know. Eric’s built a few Triumph engines from parts, so he’s been in your shoes. This is what he had to say: “All 650 unit engines had nine-bolt heads up until 1972, so there shouldn’t be a problem as long as the jugs have nine holes. They did change the threads to unified threads in 1969.” That shouldn’t matter as long as you use the head bolts you already have. MC 

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, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject. 

1973 Kawasaki H2 750 Is Running Lean 

Q: I bought a 1973 Kawasaki H2 750 2-stroke triple. It was supposed to have been rebuilt, and the guy did a compression check to show me. It had about 160psi for all three cylinders. It has oil injection, and he said it was using Bel-Ray Si-7. I filled it with premium gas and put some city miles on it, and then went on the freeway. After only a few miles at 70-80mph, it lost power and smoked a lot from the left-hand cylinder. I pulled the plugs and the left-hand one was silver. The others had a light tan color. Any idea what happened and what I should do? - Richard Langley/via email 

A: It sounds to me like the left carburetor was running lean. The ideal air to fuel ratio for combustion — the stoichiometric mixture — is about 14:1. Add more air to that ratio and you get a lean mixture. Running a slightly lean mixture is important for emissions and gas mileage. Running lean also results in higher combustion chamber temperatures and pre-ignition. When an engine pre-ignites, it fires before the spark is triggered for that cylinder. This is usually caused by a carbon deposit in the cylinder head glowing hot enough to act as the spark plug. Pre-ignition and detonation are particularly hard on engines because the explosive pressure of the burning mixture is meeting the piston before it reaches top dead center. You can hear this as knocking, sometimes characterized as the sound of marbles rattling in a can. Running a richer mixture can help tame pre-ignition via the cooling effect of the gasoline as it vaporizes in the cylinder, drawing off heat.

Silver on a spark plug usually means trouble, in the form of melted alloy from the piston being deposited on the ceramic insulator. The worst case scenario is you’ve melted a hole through the piston crown and spattered hot metal into the crankcase. If you’re lucky, you’ve only melted a bit of the crown and not gone all the way through. You should repeat the compression test. If you find reduced compression, you’ll have to pull the head off to see how much damage there is. If you’ve melted the piston clear through, you’ll have to completely rebuild the engine to ensure no metal debris finds its way into the engine bearings. If you’ve only started to melt a piston you’ll possibly need to replace that piston. You’ll definitely need to find the cause of the problem, starting with the easiest solution and moving to more complex solutions. Be certain the left carburetor is mounted correctly, as air leaks will make a cylinder run lean. Make sure the left carburetor jets are the correct size and they are clean. Check the float bowl level to be certain it holds enough gas. Once you’ve done that, move on to timing. Your Kawasaki H2 750 should have a CDI electronic ignition. Those seldom go out of time, so I’m more inclined to focus on carburetion. Still, check the timing. MC 

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, 1503 SW 42nd St., Topeka, KS 66609, or send an e-mail with “Keith’s Garage” as your subject. 

1970 Honda CB350 Custom Wiring Problems 

Q: I’m building a 1970 Honda CB350 custom with bobbed fenders, Superbike bars, painted wheels, etc. I’ve put in new rings, rebuilt the carburetors and so on. I want to ensure the bike is dependable, so I have tried to update or replace with new all the items I can. My coils and wires were questionable, so I wanted to replace them without breaking the bank. I was able to get some Wat Yong aftermarket coils from Dime City Cycles. The original coils on my 350 each had a black/white wire and the second wire on each was yellow or blue, respectively. The black/white wires both went to the harness and I assume were the source of power for the coils. The yellow and blue wires went to the points (right and left). The condenser was wired across the yellow and blue wires. Of course the plug wire on each goes to the plug. The aftermarket coils have a black wire and a yellow wire. I wired the blacks to the black and whites in the harness for power. The yellows I put to the points, left and right with the condenser wired between them. Am I in the ballpark? Does it really matter which way the wires on the coils are wired as long as the high voltage goes to the plug through the plug wire? - Lynn Metzger/Lawrence, Kan. 

A: I think you’ve got it wired correctly. I don’t see how you can go wrong, as the primary side of the coil doesn’t care which wire is hot and which is grounded. At worst you would have the coils polarized backward. An easy way to be sure is the old car tuner’s method of holding a pencil between the spark plug lead and the plug. The polarity of the coil will be shown by a shower of sparks from the pencil lead. A spark going toward the plug is usually desired. In the past, this was done to take advantage of the thermal characteristics of the spark plug. The center electrode runs hotter than the strap. Electrons are easier to push off of a hot surface. That means it takes less of the high voltage output of the coil to produce the spark. If you have the coil polarized correctly, the spark jumps from the center to the strap. Polarized the other way, it’s just the opposite. Modern engines, both motorcycle and car, sometimes share coils among cylinders, firing one on compression and the other on exhaust. On those dual output coils, one output is positive polarization and the other negative. I guess they decided the cost savings outweighed the efficiency. Lynn, I’m glad to know your Honda CB350 custom started easily and is running strong after installing the new coils. MC