It seemed innocent enough at the time. I was referred to a new customer who had a relatively low miles CB200T street bike that was set aside after extensive carb and petcock cleaning hadn’t solved the bike’s running problems. Apart from a new coil installed there were apparently no other modifications done to the machine other than a set of EMGO mufflers that replaced the rust-prone originals. How hard to it be to get it running again?
It had been sitting for close to a year, apparently, so the battery was stone-dead and needing replacement. Once the neglected machine was brought back to the shop, a new battery and some spark plugs were picked up at the local dealership and a few checks made on the overall condition of the bike and engine. The compression readings were both right about 150 psi, which is on the low end of specifications, but should have been good enough to make it run okay. These are not overly-powerful machines, but should run up to redline in lower gears without issues.
After experiencing a “wrong coil” issue with a CR93 Tribute bike a year ago, the first thing to check, once the fuel tank was removed, was the new ignition coil. Honda’s OEM coils are no longer available, so you have to go with the only available options; new aftermarket coils made in China.
Sure enough, when the coil was checked with an ohmmeter, the primary side resistance was 1.5 ohms, instead of the normal 4.5 ohm readings for a bike with points and condenser ignition systems. I ordered a correct 4.5 ohm coil and looked over the fuel system while I waited for the ignition coil to arrive from SFO distributor 4int1.com
I expected to see a set of reversed carburetor slides as a possible contributor to the reported problems, however they had been installed correctly. The needle clips were in the middle position and the needles were K marked OEM parts. Very often carb overhauls are done with aftermarket branded kits which have poorly engineered replacement parts, but this was not the case here. Despite laying up for many months the carbs and fuel tank petcock were still fairly clean and not obviously causing problems.
When the coil arrived, I installed it and screwed the spark plug caps into the wire ends, which were NGK branded parts. The bike fired up with the new battery, even on the old fuel, but the engine stuttered and balked as the throttles were opened much past half way. The engine sounded like it was choking from excessive fuel, so it was shut back off and the float bowls removed for inspection of float levels and any blocked air passages. The right side bowl came off only to find the idle jet lying in the bottom of the bowl! That explained the over-rich condition that had carboned up the spark plug on that side. The jet was reinstalled and fresh spark plugs installed. The bike restarted, sounding better, but still had a mid-range stumble. The plugs were removed for another look and it appeared that the engine was still running somewhat rich. When the plug cap was removed, I was startled to see that the inside of the spark plug cap hardware was still stuck to the end of the spark plug! Well, that would explain some misfiring!
These small Honda twins have a single, dual-lead ignition coil, so both spark plugs and caps must be secured to the spark plugs in order to fire properly. An open circuit on one end or the other causes the spark to break down immediately. New plug caps were purchased and installed after the plugs were cleaned and the bike restarted once again. More blubbering sounds were apparent and this time the left side carburetor’s idle jet was discovered to have had unscrewed itself and was lying in the bottom of the float bowl! The jet was still open, so was reinstalled again and the start-up routine repeated. The bike would start and run okay, but continued to mis-fire beyond mid-range throttle openings. Now what???
Going back through the ignition system, I checked the ignition points contact faces, which were a little dished from wear, so they were cleaned up and re-gapped to specifications. The spark advancer was checked for proper advance/retard functions and some point cam lube applied to the advancer cam surface. The ignition timing was reset to the F mark and checked on both lobes of the point cam. The opening of the points was within a degree or two of each other, so well within reason. The voltage was checked on the points when the engine was off and then running. Initially the point voltage readings were around 9 volts, but then climbed back up towards 12 volts as the engine speeds were increased. Typically, the ignition voltage should be close to battery voltage, however these 1975 and later twins have “always ON” headlights, so there is an immediate voltage draw when the ignition switch is turned to the ON position.
I opened up the headlight shell to check the wiring color matches and found the black/white stripe power lead for the kill switch (which feeds the coil) plugged into a rogue brown wire, normally used for lighting purposes. Shifting the wire back into the 4 way black connector gave a better voltage reading, however the headlight feed was also plugged into that junction. The right side handlebar switch was not the correct one for this application and normally has a blue white stripe feed going into and out of that side. The wiring was not present in the switch, so the feed wire had to be plugged into the main switched black wiring junctions, as well.
The bike was test-ridden numerous times in the local area, but no matter whether it was going downhill or uphill under load, the same high-speed cut-out misfiring remained. I rechecked the fuel and ignition systems once again, eventually replacing the ignition points and condenser, although they really didn’t appear to be defective. Most of these components are relatively inexpensive, but I don’t like to keep throwing new parts into a bike as a process of elimination to cure a problem. After many hours of checking and rechecking everything from the gas cap venting to possible muffler back pressure issues, nothing new was found.
The remaining clue was that when a dynamic timing light was connected to the spark plug wires, the light flashes started to become intermittent when the engine began the mis-firing routine again. Despite the presence of a “new” ignition coil of the correct impedance, the symptoms continued to indicate a failing secondary voltage issue at the plugs.
In desperation, a hopefully good used OEM Honda CB200T coil was purchased from eBay sellers to prove or disprove whether the misfiring is still coming from the coil or some as yet undiscovered nuance which has not been recognized. The coil arrived in just a couple of days and I was holding my breath about whether this really was the final solution to the mysterious misfire…. Honda coil installed and the bike went right to redline without any hesitation….. a LONG and winding road leading to my first inclination that the “new coil” from China was not up to specs. Apparently of the 100 or so that 4into1 has sold, I got the bad one!
Well the bike has been gone over with a fine-tooth comb and is now ready to return to its owner, ready and raring to go once again. There is no way I can get reimbursed for all of my time expended on this repair, but I have the knowledge that my troubleshooting observations were ultimately correct. Another day at the office at Casa del Honda.
Bill Silver aka MrHonda