Bad, Weak points Spark - HELP PLEASE

Guys - I'm in need of some help here. I have a Commando 850 - I have a weak spark only one side (left Side) of my Commando - I've changed the points - new backing plate - condensers and we switched sides with the coils. Nothing makes a difference. it's always the same side. I set the gap at .015 for both points and on the weak side I set the timing to 28 degrees and it shows very steady 28 degrees @3000 rpm. As far as the good side (right Side) where I have a strong spark @ the points the timing is set at 28 degrees as best i can - It's some what erratic. I mean the timing just kinds jumps around much more so than the weak side.

In other words --i'm getting a strong spark at the points on the side it's hard to set timming and on the side with the weak and erratic spark i'm able to set the timing dead on @28degrees. Anybody have guess what's gong on? The only things I have yet to change is the wire and advance weights and springs.

I just dont know where to go from here. The side where it is weak fires the cylinder some of the time when i test ride. You can feel it kick in. And then it will go just as it came- All along I thought it was the spark plug - after a test ride a week or so ago It was not firing and so then I pulled the cap off the points and could see the weak spark. That's when I checked the gap - points looked good timing was a little off so I got that right - And the points are in great shape. I changed them any way -

Also we have new carbs and valves have been set correctly. Compression is the same on both sides. Pleas any help or ideas would be most appreciated. Any thoughts?????-

bertscommando850 said:

The only things I have yet to change is the wire and advance weights and springs.

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I suggest you replace both coil to points wires (Black/White & Black/Yellow) before you try anything else?

(right Side) where I have a strong spark @ the points

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You shouldn't have a strong spark at the points if you have the condencer is goosed.

Cash

hi bert,its a long time since i had points but from what i remember i would,nt be looking for a strong spark at the points,i beleive its the condensors job to prevent arcing at the points, i would suspect a faulty condensor or maybe the wires that connect them to the points,also check the insulating washers on the points

Swap the condensor, coil and spark plug lead from the good side to the bad. See what happens. If it sparks well, then through a process of elimination put the bad side parts in one by one until the defect appears. That's your bad part to replace. If none of this works, and you still have a weak spark on the left side, its in the ignition wiring. Note that soldered joints, like those on the coil connectors after many years get brittle. Corrosion under terminal connectors makes resistance too. Remove and inspect all of the ignition wire connectors. If the joints are still firm, clean up to bright metal with emery paper. Also make sure you got the right insulating washers under the points pivots.

Mick

Would second ML in the checking for corrosion. It's absolutely amazing what the seemingly slightest bit of corrosion can do to a circuit. Pull apart all connectors and check em out. Sand up contacts with emery paper or the like. Reconnect with some dielectrical grease (better yet, solder and shrink wrap). Works wonders.

This may not be your problem - or all of it (amazing how often there are multiple causes that need to be eliminated). Good luck hunting down and eliminating the problem.

Even though the fault seems to be only on one side check your kill switch for high resistance. The feed for the coil has to pass through this connection and often looses voltage here, perhaps exacerbating other bad connections. I always bypass the kill switch with a relay and use the switch only as a trigger for the relay.

I always bypass the kill switch with a relay and use the switch only as a trigger for the relay.

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An excellent suggestion, especially for any bikes with handlebar mounted master cylinder! However, in this case I would suspect the condensers. Years ago before I threw the bloody things in trash and went electronic, there were a number of replacement condensers that would develop shorts to ground. My experiences with this was total failure, however, not just weak spark, so I would follow Les' suggestion also and make certain that the trigger leads have good clean tight connections and no frayed or broken wire.