Topic: Cylinder 2&3

[Mitchm114]

Hi everyone,

I have a 76 CF550 super sport that has been running well up until yesterday.

I’m getting intermittent fire on cyl 2-3. The pipes are cold and when I’m running it, it’ll run on 1 and 4 for a while with 2-3 working intermittently. When I’m riding it, it feels like a fuel flow issue, as it behaves like it’s out of gas or is getting restricted fuel flow, but I have fuel getting to the bowls.

Like I said, I have fuel in the bowls. I pulled the main jet out of both carbs and sprayed carb cleaner up through the emulsion tube. When I pull the plugs out, ground them to the engine and hit the starter, I’m getting Spark on both plugs. Granted, they look like the original plug wire caps, so maybe a resistance issue there?

I’m kind of at a loss. Could it be a timing issue or do I need to do more carb disassembly? Could it be an air leak on the intake? Is my coil going bad?

Can anyone point me in the right direction?

[bryanj]

How long since you did points and timing

[ekpent]

 As the guys have pointed out 1 and 4 fire from one set of points and condenser and 2 and 3 from the other. So could be a problem with that point set and condenser for that pair of cylinders. Some Dyna aftermarket set-ups have been known to lose a pair of cylinders also if you do not have the stock ignition components. I would have a couple of new spark plugs handy when you get doing more troubleshooting as you have not done the old ones any favors running the engine without them possibly firing. When you took the old plugs out were they wet with fuel ?

[Mitchm114]

I replaced point and condensers a month ago, which made it run considerably better than it had.

Swapping the condensers worked. The problem jumped to cyl 1-4. Luckily I had one of the old condensers laying around, which is a good bandaid, but the spark on the points is still arcing, albeit not as bad as before. I guess I learned my lesson to not buy cheap condensers.

I didn’t check timing when I replaced points. I just took a photo of what I had before, spaced the points and moved on down the road.

It’s running better now, but I’ll still need to get a new condenser long term.

Thanks for all your help.

[ekpent]

 Do you care to share what brand/seller etc. the new points/condensers were.Might save somebody some grief in the future or maybe you were just unlucky and got a dud.

[DaveBarbier]

I’ll venture a guess. Daiichi. Buy TEC or ND (nippon denso).

And you can’t just slap points on, you need to set the gap and timing as it explains in the manual.

[HondaMan]

I'll vote for a bad coil.

[Deltarider]

Also realise that intermittent grounding of the 2+3 breakerpoints is a possibility. The forked connectors have a crosshead in the vicinity and when not carefully fitted, they are so close that they touch eachother (sometimes intermittently) which will result in some sparking there. Are all the breakerpoints insulator rings  still there and in the right place, including the tiny one in the middle?

[PeWe]

Also realise that intermittent grounding of the 2+3 breakerpoints is a possibility. The forked connectors have a crosshead in the vicinity and when not carefully fitted, they are so close that they touch eachother (sometimes intermittently) which will result in some sparking there. Are all the breakerpoints insulator rings  still there and in the right place, including the tiny one in the middle?

+3
Very easy mistake to be done! It can happen when tighten the nut and the fork connector rotate. The part where wire is attached is very wide.  Done that many times
Almost contact can most likely become intermittent.

[mrbreeze]

Also check for a tight clean connection at the black/white wire that powers your coils. Take the gas tank off and find that wire. It runs from the kill switch and branches to 2 wires that power the coils. I had one that the female socket got a little loose to the 2-3 coil and it would work intermittent. As time went on it got worse.

[Deltarider]

Also check for a tight clean connection at the black/wire that powers your coils. Take the gas tank off and find that wire. It runs from the kill switch and branches to 2 wires that power the coils. I had one that the female socket got a little loose to the 2-3 coil and it would work intermittent. As time went on it got worse.

+1! That female socket on mine also has been loose for decades now and it's certainly something to look after.

[Mitchm114]

Sorry for the delayed reply here. I have a 3 week old over here and my time to work on the bike has been monopolized.

Here's the kit I bought to replace the condensers and points.

LINK: https://4into1.com/ignition-tune-up-kit-honda-cb500-cb550-cb750/

They were a generic aftermarket set. I'm going to get a set from David Silver Spares to replace these.

I think there were a couple things happening here..

1. One of the condensers was definitely bad. I had sparks flying all over the place on one of the points. I switched the condenser over to the other set of points and that problem followed.

2. The points were poorly made and were shorting out on the bolt attached to the cam lobe. I had to bend the edge of the points to keep it from shorting out.

3. I'm still experiencing a bit of additional spark emanating out of the top of the points on one set, but the other looks good.

4. I do think I need to set the timing with a strobe light. When I set the timing before it was mainly by setting the gap with a feeler and eyeballing the timing using the marks and the lobe. The bike runs pretty well overall, but I'm sure it would run much better with the precision of the strobe light.

I'm going to go ahead and check the nut and fork connecters on each points set to be sure they aren't shorting. I'll be sure to check that those rings are there and placed correctly.

I'll also check the connections on the coils to be sure.

On an (sort of) unrelated note, should i change caps on my plug wires? I'm pretty sure they're original. The bike has 16k on it. I haven't noticed any sparks jumping to the head when I run it with the lights off in the garage. I was curious as to whether I should change them out proactively and which ones I should look for.

Thanks everyone for your help.

[Deltarider]

On an (sort of) unrelated note, should i change caps on my plug wires? I'm pretty sure they're original. The bike has 16k on it. I haven't noticed any sparks jumping to the head when I run it with the lights off in the garage. I was curious as to whether I should change them out proactively and which ones I should look for.

You can check them like this. Start with checking the total resistance from one plugcap via the coil to the other plugcap. Realise that new resistor plugcaps are around 5kΩ. When over 8kΩ, replace. The coils secundary itself is around 14kΩ, so with both plugcaps attached you should read 24-30kΩ in total. When you read over 30kΩ, unscrew both plugcaps to be tested individually. Over time the plugcaps resistance tends to increase and a lifespan of 16k in my experience is pretty close towards the end of its reliability. Do not run resistor caps and resistor plugs. When you have the choice, I'd prefer resistor caps over resistor plugs. Verify plugcaps are well connected to the wires. Oh, and here's an a vid showing a good and a bad condenser. I am confident by now you can tell the bad from the good one.

[Stev-o]

I'll vote for a bad coil.

Hey HM...how often does that happen?  I've never had one go bad.

[RAFster122s]

Remove the spark plugs caps and trim about 1/4 inch off the end of each, cut them cleanly. Then replace your caps. Don't trim if you have wires that are too short already... Better then to just replace the coils with a pair of 5 ohm coils from cb750supply... pretty sure that is the set HondaMan recommended.  They are less than $100 for pair of new aftermarket coils with wires built in

[HondaMan]

I'll vote for a bad coil.

Hey HM...how often does that happen?  I've never had one go bad.

Lately (last 6-7 years) I am party to helping someone find their coil(s) have gone bad. The insulation on the wires inside the coils is enamel, and thru some investigation I found that these were intended for a 10-years service life before the enamel might lose its elasticity and start flaking off. The failure mode is: when cold they often work and will idle OK, but won't rev up well: they tend to either resist passing 5500-ish RPM or they just start backfiring and sputtering. Inside, the wires have shorted one to another in layers of the coil. The measured resistance hot was lower than when cold (by about 100-ish ohms on secondary side), which was my only 'clue' to the failure mode.

My brother's CB500 did this on the 2-3 side in 1978 while he was crossing Kansas enroute to Missouri after we had toured the Southwest in August (no, that wasn't smart...) together, and my 750 lost the 2-3 coil in almost identical manner in 2007 during a particularly slow, hot (109 degree day) commute home from work. My 2-3 quit firing, and when I pulled into a gas station to check plugs (after cooling it for 15 minutes) and found them fine, it started right up and ran another 10 miles before doing it again. It took 3 more times of this to get home, had a 50 mile commute in those days. I installed another used 2-3 coil I had and ran it that way until 2018 when I got new coils. The 1-4 was still my OEM one, but upon changing them both, the cold-bloodedness it had developed about 2012 or so disappeared. So, it can have more than one symptom!

[PeWe]

Checked where points wires are connected to main harness?
If the yellow wire sit loose.
Blue 1:4, yellow 2:3.
Work the other way if rotor sit wrong.

One more thing: If using NGK plug caps. They are rather brittle and can easily crack causing intermittent ignition misses.  Usually only 1 cylinder.

I cracked one when testing ignition to see the plug working using an extra plug. I held the wire with  plug in cap, dropped it and it fell hitting the cylinder. I did not notice that the cap cracked then.
Noticed while riding. Remembered what I have done last and saw the problem.
These NGK 5 kohm caps are good to have a spare set of since the can crack really easy.

Maybe thin cracks that will cause problem while raining.

[Mitchm114]

I just wanted to follow back up on the ignition issue to bring some closure.

I went ahead and purchased a NOS points plate with all the requisite parts. Put it on night before last, set the gap, timing, and fired it up. The bike ran like a dream. I don't remember it running so smoothly before or having that much power, so I'm guessing my old set of points were pretty worn, and the condensers weak. I admit, it may just be psychological, but I really noticed a big difference.

I still need to run down the plug caps, but that's next on my list after patching up my exhaust. I have the original header on it, but it's starting to rust through at the point where the muffler meets it. I just have a cheap aftermarket muffler on it now, might upgrade to something else, but I just like the look of the original header.