Monday, December 27, 2021

Pointing to the past…

I subscribe to many FB forums, plus have my own stream of customers who contact me through my website: for help with their 50-60+ year old vintage Hondas. For those who are coming new to the hobby and the mysteries of old-school motorcycles, the subject of “points and condenser” ignition systems comes up often. In the 21st Century, the prevalence of electronic and CDI ignition systems overshadows the 20th Century ignition systems, which appear primitive by design.

The points and condenser ignition system, originated by Charles Kettering, is described on many websites like: and

As applied to vintage Honda motorcycles, the function is the same as the automotive systems, which had distributors to feed sparks to multiple cylinders, one at a time. On a simple motorcycle engine, the ignition systems started out with self-powered magnetos, which mostly have a fixed ignition timing and do not require a battery to power the units. 

Early Honda 50-70cc models all have magneto ignitions, most of which are fixed spark advance designs. Small-bore engines can run successfully on a fixed ignition as they are easy to kick over and start and the spark timing doesn’t cause undue engine heat buildup as what would happen on a larger displacement engine. In the case of the first-generation Honda Cub 50cc models, the kickstart models had 35 degrees of spark timing built-in. However, the electric-start C102 models needed a retarded spark timing to allow the starter motor to more easily turn the engine over at cranking speeds. So, only those models have a mechanical spark advance system built into the flywheel.

Magneto ignitions use a set of contact points and a condenser to manage spark production. They are “live” all the time, so in order to shut the engine off, you have to have a “kill switch” of some design to short the primary voltage to ground. When Honda went into the realm of CDI (capacitive ignition systems) in the late 1970s, they were also self-powered and required a kill system to shut down the sparks.

In their basic form, the ignition points are a variable switch that turns the ignition coil on and off. They are variable, in that the point gap can be adjusted by changing the point base in relation to the spring-loaded, movable point arm, which is operated by the rubbing block. The rubbing block rides on the eccentric point cam and follows the profile of the cam lobe.

                                                  Drawing from AHMC training materials

The problems with the point system are that the rubbing block eventually wears down a little at a time, which reduces the point gap. As the gap decreases, the opening point becomes later and later, which delays the spark timing to the engine. On a normal tune-up, the contact faces are cleaned with an abrasive to increase metal-to-metal contact which ensures more voltage going to the coils. Then the point gap is enlarged by the adjustment of the point base screws. This brings the ignition timing back to factory specifications and ensures proper engine performance. To reduce the amount of wear on the rubbing block, high-temperature grease is used to lubricate the point cam. On some point plates, a piece of oil-absorbing felt is located next to the point cam and a drop of engine oil keeps it wet and lubricated.

The point contact faces are generally made from a metal called tungsten, which has high resistance to arcing and metal transfer when the points open. When the points are closed, the current is allowed to flow through the ignition coil building up a high voltage charge. When the points are pushed open by the point cam, the voltage flow is interrupted and the points are subject to an arc/spark which jumps across the faces as the voltage tries to maintain the connection. The use of a condenser in the circuit absorbs the arcing force momentarily, then discharges it back to the ground when the points are closed again.

In battery-powered ignition systems, the power flow is from the battery to the ignition switch, then to the ignition coil. Some models will route the power through a handlebar-mounted kill switch so that the ignition can be switched off quickly in an emergency or to shut the bike down without reaching for the ignition switch. A defective kill switch can cause “no-spark” issues when the contacts become corroded or the connecting wires to and from the switch are loose or grounded by a pinched wire in the handlebar switches.

When all the wiring is intact, the battery voltage routes to the ignition coil which generates several thousand volts when the points are closed. The coil discharges the spark energy when the points are opened, dumping the high voltage out of the spark plug wire to the spark plug where it jumps the plug gap and creates a kernel of energy that ignites the fuel/air mixture inside the cylinder’s combustion chamber.

The timing of the ignition is critical to the engine’s performance as the fuel mixture is compressed prior to combustion. At slow idle speeds, the spark timing should be about five to ten degrees before top dead center on the compression stroke. As engine speed increases, the time available for the combustion charge to ignite also needs to speed up, and the spark timing is advanced by the point advancer unit.

The spark advancer is generally a system of weights and springs where the springs hold the weights in retarded mode and then the weights will overcome spring tension as the centrifugal force increases with engine RPMs. The weights pivot on locating pins and interact with the point cam at the base where the point cam rotates on the advancer base shaft. The point cam then shifts the opening moment earlier in conjunction with the increase in engine revolutions. Full spark timing advance generally occurs about 30-45 degrees before top dead center of the piston above 3,000 RPMs.

The configuration of the engine in regards to compression ratio, cam timing, and shape of the combustion chamber dictates how much spark timing is required to make the best use of the fuel available. When spark timing occurs too early or late, fuel energy is wasted and results in unburned fuels going out of the exhaust system which is a major contributor to air pollution as well as poor engine performance and dismal fuel economy results.

Spark timing directly affects the engine’s manifold vacuum signals to the carburetor metering circuits. As spark timing advances, the engine vacuum signals rise pulling in more and more fuel through the idle and main metering channels. In the case of the archaic spark advance systems in the 1960s Honda 250-305cc twins, the mechanism for advancing the spark timing is inside the camshaft sprocket and not serviceable without engine removal and splitting the two cams apart in order to remove the sprocket assembly.

This system, designed in the late 1950s, seems to be compact and self-lubricating, however, problems occur when the springs lose tension, the weights wear out on the pivot pins, and the little molded rubber stopper cushions on the weights either compress or dislodge from the weight faces. Furthermore, the camsprocket is basically riveted together and the rivets loosen up after many miles causing erratic camshaft timing as well as ignition timing irregularities.

All of these factors create a condition where the spark timing advances prematurely at idle from the normal five degrees before top dead center to twenty or more degrees. With increased spark timing the engine responds by speeding up unnecessarily. The engine speed increase causes more fuel to be drawn through the idle circuits further fueling the tendency to increase engine speed further. This snowball effect overcomes the carburetor’s ability to control idle speeds by the use of the idle speed screws and idle mixture screws.

On the market now are several electronic ignition systems that do away with the points and condenser, but still rely on the mechanical spark advancer for that function. These systems are magnetically triggered and are mostly immune to any wobble at the advancer in the case of the 250-305s. offers the most affordable solution to replace the twin sets of points and condensers of the CB/CL72-77 Honda twins (1961-67) for $159, as well as a designated system for the single point 250-305 Dreams ($139) plus a regulator-rectifier for $39.

There are other companies offering ignition systems for vintage Hondas including Charlie’s Place and a company in Germany that makes a crankshaft-mounted system for the 250-305 twins. Prices range from $250-400+

While OEM points and condenser ignitions were perfectly fine for their uses when the bikes were built in the 1960-70s, the new electronic systems are maintenance-free and provide a clean trigger signal to the ignition coils for a fast and maximum spark burst to the spark plugs. Maybe it is time for you to bring your bike’s ignition system up to 21st Century specifications now.

Bill Silver

aka MrHonda

Friday, December 10, 2021

What’s next? A pair of twins…

Having just cleared off the work table lift of the last CB77 project, I was contacted by my friend Michael in Orange County who had rounded up a pair of CB175s. Both bikes had very low miles showing on the odometers, but the mileage indications were backed up by the fact that three of the four tires on the bikes were original Yokohama tires. Someone had replaced the rear tire on one bike with a 3.50×18 tire, but the edges were getting chewed up from contacting something inside the fender area, so it needed to be replaced as well.

The pretty turquoise bike was from late 1970 production with a 5 (K5) serial number. The bike had the original front brake light switch embedded into the cable, but the handlebar bracket was black on the bottom and shiny silver on top. Apparently, someone tipped the bike over, broke the bracket with the mirror hitting the ground, and then replaced the lower half of the switch with one from a 1972-3 model. The other concern was that the clutch lever was VERY HARD to pull in, indicating the possibility that the clutch springs had been replaced unless the clutch was stuck or the release mechanism is rusted up.

The bike has been refitted with an electronic ignition, but the engine was not running well on one side. Compression readings were 175psi and about 155 psi. The spark plug came out looking kind of oily wet, so it is possible that the engine was overheated and had a partial seizure, causing oiling of the plug.

The Gold bike had not been run for a number of years, so would need the most repair work, but you never know until you dive in and find the problems and solutions.

On to work…Goldilocks goes first

I rolled the gold 1971K6 bike up on the work bench, drained the dirty oil and checked all of the valve clearances first. The carbs were gummy, so were removed and cleaned in my little ultrasonic cleaner. It is always necessary to replace the flattened out o-rings on both ends of the manifolds, which I happened to have in stock. Speedometer was reading about 2800 miles and the front tire was the original Yokohama while the back one had been replaced with an over-sized 3.50×18” CS brand tire.

The left air cleaner cover had a broken tab on the rear which had been glued up with some unknown adhesive but broke again. I wound up replacing all of the frame rubbers for both side covers and used JB-Weld to repair the broken one again. Silicone grease was used liberally to rubber and side cover tabs to reduce further damage.

The Charlie’s Place e-ignition system had been installed with a new coil, but giving the trigger wheel a twist with my fingers revealed that the spark advance function was locked up. The spark timing setup didn’t look accurately installed either, as the magnets were not aligned with the pickup module center-line. The spark advancer assembly was pried off of the end of the camshaft and using Charlie’s online PDF installation instructions the advancer was disassembled and a small locating pin was ground down to allow the ignition rotor to fully advance normally. Setting up the timing is easy with these systems as you only need a 12v test light to probe the connector wires and turn the engine until the F mark lines up. If set correctly, the light turns ON and you are good to go.

After refilling the engine and reattaching the carburetors, I fed the carbs with a remote gasoline tank and fired the bike up. It sounded pretty good, but started to run rich at idle even with the mixture screws out way beyond normal. All the carb jets were OEM parts, but either the idle jets had been enlarged or perhaps the floats were sinking. Compression readings were right about 160-165, so the engine seemed to be sound and should be with 2800 miles showing on the odometer. The valves were adjusted, but were pretty close to specifications.

The gas tank got a phosphoric acid treatment followed by a dose of Caswell epoxy tank sealer product. The petcock feed tube was missing, so the remaining part of the tubing was drilled out and a 4mm tube installed in order to save the part. New gaskets and a screen brought it back to normal function again.

I got an unexpected box of spare parts in the mail from Mike, including an invoice for about $800 for work to install the e-ignition system from a previous repair shop. There was a few lines that included a camshaft and spark advancer too. In the box were the broken parts, including a camshaft with the spark advancer portion broken off and the advancer with the end of the camshaft still stuck inside. Obviously, the ignition system installation went sideways and a lot of money and parts were needed to make it whole again. The date on the invoice was 2019! You just never know about these things...

The next day…

After cleaning the carbs carefully, earlier on, the only remaining reasons for rich idle mixtures are idle jets that are too large, sinking floats or blocked air bleed passages. First pass was to remove the OEM idle jets and compare them to some spare a/m jets that were leftovers from a different project. I use a set of tapered jet reamers to clean out jets or just as a gauge to see if all the jets are the same size. The removed jets swallowed the whole jet reamer that was barely able to fit through the replacement jets. Using one of those cheap welding tip cleaner tools, it appeared that the jets were bored out to somewhere in the #45-48 size! Mystery solved, as the replacement jets cured the idle problem completely.

All that remained was to change both tires/tubes and take it out for a good test drive to check out everything else before turning to the little turquoise bike. The tire change took an extended period of time, as the brake drums and inside edges of the rims were rusted and needed a fair amount of time with a rotary wire brush and scraping with a flat-bladed screwdriver. When bikes sit for a long time, the air pressure drops down to near zero and the tires come off of the beads allowing moisture to enter and create rust spots. It is pretty much expected on bikes that are 50 years-old now.

If the same guy worked on both bikes previously, I had a road map of what to expect on bike #2.

Little Blue Boy, bike #2

This pretty turquoise 1970 CB175 had the stock muffler on the left side and a 354 code CB200T muffler on the right side, which fit perfectly. This bike had been running a few months before, but Mike complained that the bike had “over-heated,” during a summer parade ride and hadn’t run properly since.

The compression was a little low on the left side, so a valve adjustment was performed and there were several tight valves that needed to be adjusted. Afterward, the compression readings pretty much matched up to each other, so that alleviated having to tear down the motor for valve work or maybe tired rings. I injected grease into both bikes' grease fittings for the clutch lifters, which lessened the clutch pull quite a bit.

This bike had a Chinese-made Tytronic e-ignition plate installed, but the magnet alignments seemed to be off-target. The system is supposed to have a tiny LED light that turns ON and OFF when the timing marks are aligned, but the light had failed to function. The only way to check the timing was with a dynamic timing light with the engine running. The rotor runs in oil on these engines so they tend to spit out oil when the cover is off, but that was the only way to confirm the correct timing of the unit. It took about three tries, but finally, I saw the correct alignment of the marks, so closed it up, drained the oil and refilled it with fresh 10-30 Honda GN4 oil.

The bike got a new AGM battery installed, as its original AGM was robbed for the gold bike. The carb bowls looked clean and the idle jets were properly sized. When run off of a separate fuel bottle, the engine started up quickly and settled down once it warmed up a bit. A test ride went well going downhill but on the return run, it faltered as if it was either seizing or running out of fuel. After switching to reserve and waiting for a moment, the engine caught back on and got me back home again. As I inspected the gas cap, I noticed that it was some kind of aftermarket cap with an edge vent hole that seemed to be pinched off during assembly. I switched to a known good cap and rode the bike for another 20 minutes without incident.

That bike had both of its original tires replaced with some Michelin City scooter tires, which are one of the few options in the correct tire sizes. The tire sizes for the CB175 are the same as specified for the 305cc CB72-77 Super Hawks, which have seventy-five more pounds of weight and 50% more horsepower. When I checked local motorcycle dealerships for some inner tubes, none of them carried anything smaller than 3.50×18.” How times have changed…

Bill Silver aka MrHonda