Topic: Question for the experts

[dudeman750]

Guys, I have a wierd problem. I have a 1982 CB650SC. Before winter I put new plugs in, new copper core wires, new boots all around, new connetors at coil, new plugs, rewired the coils carefully. I am an electronics tech, and a DIY mechanic. Oh yea, new NGK 5K caps. Anyway throughout winter I noticed when I fired it up that the headpipes on the 1 and 4 were cold. Yesterday I got to looking at the plugs. After 5 mins, the 2 and 3 head pipes were hot and 1 was just barely warm. 4 is dead cold. Pulling the 4 plug and grounding the electrode I get no spark. The weird thing is if I pull the plug away from the head I get a major spark to the head from the threads of the plug. Same thing on #1 but on num 1 I get weak spark from the center electrode back to the ceramic insulator. If I take the plugs out of the caps, I get an arc from the coil input terminal to the mounting bracket. (yes I know you shouldnt do this) I have the 2 ohm (grey) dyna coils, some napa copper core wire, 5k NGK caps, and the DR8ESL plugs. Is it just a bad coil? I can swap them around with some work... but this should be easy for an expert to figure out by the probs. I was really confused doing the ingition due to the resistance factor in the caps, plugs and wires. I never found a post with a definative DO THIS IT WORKS solution. I have had ignition woes ever since I got the bike last summer. 2 and 3 run fine so immediately I would think coil, or something in the 1 and 4 pickup circuit. Is the resistor plug/ 5k cap thing bad? I couldnt find any other easy solution with todays availiable parts.


Any thoughts? I would like to ride the thing soon.

[bryanj]

From what you describe it has to be a bad plug and/or high resistence in the HT side, I do know that the ignitors can fail but usualy they work or not, they dont fail a little bit. Also not sure if those coils are suitable for the honda electronic box 650 was not so common over here in UK so didnt see many faulty ones

[Bodi]

That's a classic fouled plug symptom, firing from the threads to frame without firing the gap. There's something (usually carbonized oil) conductive between the centre electrode and the shell - it should be pretty obvious on the centre insulator. Very rarely a plug is bad inside, but I've only seen one bad plug in 35 years that was actually shorted internally.
Resistor plugs plus resistor wires isn't the best situation but should still spark OK. The spark you saw from the wiring/cables is a bother, possibly this is happening - and bypassing the plugs - all the time?
Whatever, try new plugs and see if you get a spark in the gap when tesing with the threads held to the frame. If not, look for trouble with the cables and/or caps. Testing the actual coils vs ignition box is easy, just swap the coil input wires. This won't run the bike, but you will see if the bad sparking is with the 1-4 coil or the 1-4 ignition electronics. Running the engine in a dark garage (not too long so you die) lets you see any sparking from wires/coils.