Motorcycle Repair: honda cm125, electronic ignition system, competent mechanic

Question
hi..i have a 1982 honda cm125. it has a problem. i bought it in april & it ran like a dream for 2 days. it started ok but when i put it in gear and tried to move it either died or moved so slowly you could walk faster. i changed the plugs and it sorted the problem and ive had problem free riding since..until last week when it started again. i put new plugs in but it hasnt sorted the problem.ive also done an oil change. i tried it few days ago..it popped and coughed and chugged along for 300yrds then cleared and was fine. tried today..it popped, coughed, chugged and died. any ideas? please help if you can. many thanks

Answer
Karyn,

I'll assume that you are not in the US as there were no CM125s over here.... only CM185s and CM200s, but the bikes and engines are all based on the same design. I had a CB125T from the UK brought over in 1977 and the basic design continues to this day, I believe.

What I am not sure of is whether your bike has points and condensor or the usual CDI electronic ignition system. The 1982 CM200s here had electronic ignitions. In either case, if the bike can be started, try to get a timing light on the ignition side to see if the spark advancer is operating correctly. You can check it manually, by removing the 3 screws of the cover and looking at the spring loaded mechanism. Try to twist the advancer unit and see if it turns and springs back by itself. If it is sticking or not moving easily, it needs to be removed, cleaned and lubricated.

I suspect that you may also have some fuel system contamination issues. There is a small drain screw on the bottom of the carburetor float bowl that I would open and drain the fuel into a small cup or container and look for signs of water or debris. The carburetor may need a good overhaul or at least cleaning by a competent mechanic.

Also, there is a fine mesh nylon screen inside the fuel tank, that is part of the petcock (fuel valve) and that should probably be checked and replaced or cleaned. If the bike has been sitting for many years, moisture collects inside the fuel tank and causes water droplets and rust to form inside. The rust particles will block fuel flow and can also work their way down the fuel system into the fuel jets.

The last thing to be concerned about is the condition of the battery. If it is a couple of years old, it may be dying. If the charging system is having issues, then the battery will get low and the electronic ignition may then not have enough voltage to operate the ignition system.

When the bike dies, remove the spark plugs from the head, lay them on the head with the wires attached and check for a good spark. While they are out, look for signs of fuel fouling (black deposits) or oil fouling (wet and more brown). Depending on how many miles are on the engine, it may need some mechanical attention.

You can log into: http://www.powersportspro.com/Partsfish/Login.asp
sign up and then search for the CM200 model Honda for an online reference with illustrations of the parts involved. They should be similar to your machine.

Bill Silver