Ignition Coils

[Anonymous]

Is it possible for an ignition coil to be weak or going bad? Or is it like being pregnant, you either are or your not. I have a 79 GS 750E w/18,000 miles, 4-one headers, megaphone exhaust. The bike is super fast for its age. The problem is the 2&3 cylinders appear to be running rich when you pull the plugs and look at them. They do fire most of the time, however 2 fouls out sometimes. Is it possible that the plugs aren't getting enough spark due to a coil problem? The Carbs, Mikuna 26mm have been rebuilt and the tech says that they are not the problem. Could having wrong size jets be the culprit? Does anyone know what size I should use? Love the bike and I don't want to sell it, but I gotta have a bike I can jump on and ride. I don't want a garage dweller.

Thanks, Herco

[Anonymous]

Before you go any further, try removing and cleaning the wires to the coils first.((not the spark plug wires.)) Then check the plug caps to see if the connections are solid. Then use an ohm meter to check the primary and secondary windings of the coils. the specs should be in your repair manual.

[saaz]

If you have points still, also check the condensor and the condition of the points. If there is an intermittent spark then there may be a coil problem.

All the carbs should be set up with the same jets, float levels etc.

[Hap Call]

Coils can start to go bad but normally it is along the lines of functioning properly until they heat up then the coil fails.

Hap

[Anonymous]

You sure they are not oil fouling?

Are you sure you are not getting any oil build up fouling them out. If they are getting crudy after a short period of time the cylinder of that plug may not be in good shape.

[earlfor]

Re: Ignition Coils

I have a 79 GS750E, points ignition and 24000 miles.
The first thing I would do is pull the tank and check all the electrical connections and plugs/wires. specifically the connections for the number 2 coil which runs cylinders 2 and 3. Next, I would check the point gap on the right side point set (cyl 2&3). It must be within tolerances. ( I set .014) The point surfaces also must be smooth....no pits or spikes.
Also check the connectors on the two wires the come from the point case (black and white) and are plugged into the harness underneath the left side cover behind the air cleaner box. If the connector/clips are corroded, that could be the cause of poor running.
The next thing I would do is to put a timing light on it and check to be sure timing is on the marks at full advance.
That will be at about 2500 rpm and it should be on the F3 mark. (To read dynamic timing on #2 and #3, the timining pickup needs to be attached to plug wire #2 or #3.) Timing must be on the mark, either retarded or too much advance will cause dirty plugs and poor running.
If these things are correct, then the next thing I would check is carb balance as unmatched slides will cause incorrect mixtures and can foul plugs. Cylinders 2 and 3 should have slightly less vacum than 1 and 4. This needs to be done with a mercury manometer. If everything is kosher and the bike is still fouling plugs, I then would look into possibly a weak coil. Incorrect vacum/slide settings will result in poor mixtures and poor running and I do not think the problem lies with your jetting.

Earl

Is it possible for an ignition coil to be weak or going bad? Or is it like being pregnant, you either are or your not. I have a 79 GS 750E w/18,000 miles, 4-one headers, megaphone exhaust. The bike is super fast for its age. The problem is the 2&3 cylinders appear to be running rich when you pull the plugs and look at them. They do fire most of the time, however 2 fouls out sometimes. Is it possible that the plugs aren't getting enough spark due to a coil problem? The Carbs, Mikuna 26mm have been rebuilt and the tech says that they are not the problem. Could having wrong size jets be the culprit? Does anyone know what size I should use? Love the bike and I don't want to sell it, but I gotta have a bike I can jump on and ride. I don't want a garage dweller.

Thanks, Herco

[Anonymous]

It is possible for the coils to go bad slowly over time. I had it happen to my 1100G. it felt like it was a clogged fuel jet with power surges on and off. best way to check is to switch positions/plugs and see if it changes.
But you'll get good advise here from others as well.
GY

[Anonymous]

Thanks for all of the info. After the Hollidays I am going to switch some things around and see what happenes. Maybe I do have a bad cylinder, but aren't the plugs usually more ashen than black when that happens? Once the bike is good and warm, and I've cleaned up the number two spark plug, it doesn't smoke a bit.

Merry Christmas all,
Herco

[earlfor]

The color youre looking for is the color on the center ceramic inside the plug. any color between light tan to a very dark brown is OK.
I have my carbs adjusted how I like (on the rich side) and the plug colors are a dark brown. Its safer to run too rich than it is to run lean.

Earl

but aren't the plugs usually more ashen than black when that happens? Once the bike is good and warm, and I've cleaned up the number two spark plug, it doesn't smoke a bit.

Merry Christmas all,
Herco

[Anonymous]

Coils & measuring Ohms

It is possible for the coils to go bad slowly over time. I had it happen to my 1100G. it felt like it was a clogged fuel jet with power surges on and off. best way to check is to switch positions/plugs and see if it changes.
But you'll get good advise here from others as well.
GY

Coils can be a bit tricky. I've had no-start machines with No-spark and perfectly "normal" coils as measured with an ohm-meter on primary windings and the secondary windings,changed out coils then everythings fine so........I tend toward the coils myself.
Rick........