Question
cb125s
I bought this bike about a year ago (my first bike), and have about 3 hours total drive time on it.....I have taken it to 2 mechanics, and have beaten my own head into a wall trying to get this thing to work properly. I took everything apart cleaned everything, pained it, and put it back together.... after that I rode it around the block once.... got it back to San Diego and it wouldn't work..... tried cleaning carbs, buying new coils, buying air filters, even a new carb.... Nothing worked. Took it to mechanic #1 he got it to run, and rode it back to my house (about 4 miles) and the bike died half a mile from my house.... he told me it was a fuel problem and left with money in his pocket, and I was back to square one. I cleaned the petcock, changed fuel lines and inline fuel filters still nothing..... It sat a while more and I took it to my dad in Orange County left it there for several months for him to figure out... he couldn't detect the problem so we took it to mechanic #2. This guy helped a little.... told me I had to run the original air filter or re-jet the carb to get it to work, and found a switched wire and a blown fuse.... I got it back to San Diego and rode it to my work (1 mile away from home) for about 2 weeks, and then BAM! NOTHING! no spark... so tried to clean my connections.... charged the battery, checked the float, checked everything I can think of.... I just don't know what to do. is there something I need to know about this bike? why is it so temperamental? Any advice helps.
Much thanks,
Nikki
AnswerNikki, From 1975 onwards, the bikes were wired for Headlights ON, anytime you turned the ignition switch to the ON position, whether the bike is running or not. That takes a big surge of juice from a 6v battery, so if the battery isn't fully charged and load tested, then the power to the ignition system suffers and the bikes become hard/impossible to start. Some people have put a toggle switch in the headlight wiring to give the system a break from the big drain.
On the other hand, if the wiring isn't done to factory specs, either the charging system will overpower the lights, blowing them out and blowing the fuse due to excessive voltage/current.
You do have to look at the whole picture, as you have various components which can cause poor performance. The whole fuel system must be clean and the venting for the gas cap needs to be operable. The petcock should be cleaned and the rubber components replaced.
http://www.cmsnl.com/honda-cb125s-1976-usa_model413/partslist/F++11.html#results
You must have: Spark, compression, fuel and air to make an engine run. Spark, sufficient at the right time, fuel ratios correct, compression around 150 psi and clean air fed to the engine to make it reliable and consistent.
From your photo, anytime fuel tanks get painted, there is usually a chance that overspray has landed inside the tank and then flakes off into the fuel system/petcock/filters, lines and jets.
If the handlebar switch wiring has been altered into the harness connectors, you may have too little or too much voltage in the system.
If the valves haven't been adjusted they could be too tight to allow for full compression.
Altered air filters will change the flow characteristics of the air/fuel ratios being fed to the carburetor. If the jetting is too lean, you can seize the piston. Too rich and you foul spark plugs.
I built a 1974 CB125 into a reliable roadracer that ran over 80 mph and won two championships with it in one year. It isn't the "fault" of the bike's design, but probably a lack of competent modifications done to it which is troubling you now.
I'm here in San Diego area, so keep in touch if you haven't figured it out soon.
Bill Silver
