QuestionThe last couple of times that I was riding in the rain on my 1980 Honda CB750C, my bike suddenly started running really rough. Checking around on the bike I wetted my gloved hands and tested each of the exhaust manifolds. The center two pipes cylinders 2 and 3 were cool. Is there a likelihood that this is a bad coil or bad connection to the coil? If not is there anything that I should check?
I have pulled the spark plugs and they are clean and firing correctly when it is dry out. There is a little carbon around the base of the plugs but by no means heavy deposits.
AnswerHi Erik,
Cylinders 2 & 3 are on the same ignition coil.
It's possible that the 2/3 coil is defective, has a defective spark plug lead, defective plug cap, or defective or loose wiring on the primary side (low voltage side).
Added that the problem occurs when it rain, I suspect the problem is caused by water shorting. Current leaking somewhere and shorting to ground via conductive water.
Do you have a VOM (multimeter)? Do you have the service manual?
If you want tech files on testing and troubleshooting, send me your email address as requested and explained in my instructions. I'll return several tech files to assist you. See sample files below...
Respectfully,
Mark Shively
Dielectric Grease Therapy
Here’s a fairly quick and inexpensive way of preventing electrical problems and other miscellaneous diagnostic codes on your motorcycle.
Water is a great electricity conductor. Sometimes, water can find its way into a connector producing a temporary short circuit which will then give an error code to your computers. Dielectric grease prevents water shorting at connectors. Also prevents corrosion formation on connectors.
A loose connector doesn’t make a good conductor and may produce heat which can melt plugs and connectors. This is the main cause of regulator/rectifier failure.
Buy a tube of silicone dielectric grease and go through the entire wiring on your motorcycle. Work dielectric grease into each connector. All wire connectors should be serviced for best protection. Removing the tank and bodywork may be necessary in some cases, but its well worth it. Dielectric grease will get rid of the problems, or at least help prevent them.
Afterwards, you shouldn’t get false error diagnostic codes just because you simply washed your pride and joy.
You may discover loose connectors that could have been troublesome if left unattended.
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Intermittent Electrical Problems
By Mark Shively
The symptoms you're experiencing are likely a loose electrical connection causing poor conductivity under certain conditions.
Electrical diagnosis should be performed to verify the integrity of components. For example, I've found broken solder lines on printed circuit boards before causing similar symptoms. Keep an open and investigative mind.
Disconnect all electrical connectors one at a time and clean as necessary. Apply dielectric grease and then reconnect connectors. This may identify the source of the problem.
Some connectors become greasy or oily, corroded, burned, or otherwise dirty. This poses a threat of electrical flash-over (more common with ignition spark plugs and plug caps). Current takes the path of least resistance. A flash-over condition exists when grimy build-up becomes conductive, resulting with intermittent supply of electrical current to components.
Dielectric grease helps to prevent water shorting caused by rain and washing.
