Topic: No spark on 2 & 3

[quidger]

On 1975 CB550 I get no spark from the #2 and #3 plug wires. 1 & 4 have a strong spark.
Should I look at anything other than the points & condenser as being a possible trouble source?

[1timduke]

Did this happen all of the sudden, a slowly developing problem, or was it like this when you got it?

The connections between the items in the system are also suspect, are there new plugs in it?   Are you verifying spark by holding the plug to the head or because the headers aren't getting hot?   If you're holding the plug to the head and get no spark, most likely ignition, if you do get spark, but no fire, then you have to look at the old formula... Air/fuel mixture, compression, and spark are the three things.

I thought I had an ignition problem for a few days, turns out I left out the screws in the carb manifold after the carb sync, had mixture too lean to ignite    Keep looking and let us know.

-Tim

[quidger]

The bike came out of a barn after 5 years and I have been trying to get it started.
New battery, new spark plugs, removed carburetors and cleaned. It started once and then it sat for a week until I tried to start again. It started one time. When it started it was like it was hitting on two cylinders for 30 seconds or so and then the other two cylinders kicked in for 10 seconds before it died. Thought it was weird so I put a screw driver in each of the plug wire sockets and there was spark in #1 & 4 but nothing in #2 & 3. I did not change the points and condensers yet and I think that is the issue. Spark is strong to #1 & #4 so I don't think it is a coil issue but I would like some input from more experienced members.
I appreciate the help.
Forgot to mention that I did pull off points cover and turn the engine over and I could see spark at the 1-4 points but did not appear to be any spark at the 2-3 points

[XxDarkEuphoriaxX]

are you supposed to see constant sparks at the points or only one spark on each point every couple of seconds?

[magnum56]

Start with normal tune-up steps, attempting to check and set the point gap and ignition timing as a service manual describes.  It may not be necessary to replace the points and condensors.     

[TwoTired]

Point contacts are not noble metals.  Meaning they will oxidize over time.  The oxidation layer is resistive at best, insulative at worst.
You can make them conduct again by using a points file on the contact surfaces.  Sandpaper will work in emergency if you plan to replace the points near term anyway.
Next are the capacitors which can deteriorate over time as well as disuse.  Can be checked with a DMM, or better yet, a capacitance checker.

Both these items are addressed as part of the 3000 mile/ 3 month tune up check list these bikes should have.

If it's been sitting in  barn for 5 years, it would appear to be well overdue for scheduled routine maintenance, and it has every right to not run properly until it has had, at least, that done.

[quidger]

I checked the valve clearance, changed the oil and statically timed the ignition points. I do plan on replacing the points and condensers. First priority was to get the engine running, time it using a timing light and then check the compression to see how that looks.

I'll lightly hit the points with a very fine sandpaper since I don't have a points file. Wouldn't be surprised if it is something as simple as some build up on the points. The springs on the points do have a significant amount of rust in that area. So it stands to reason that the points could be suffering the same malady.

Thanks to all for the advice.