Topic: '74 CB550 Misfire - What else can I check?

[TPIGroove]

Hello all. I have a 1974 CB550 that I rebuilt and have been riding around this summer. I had everything dialed in and it was running great for a little while, however when I went for a short ride into another town last week, it began to bog down on me. The engine began to misfire for some reason, and I was barely able to limp it back home. Since then, I've taken a good look at it.

-Cleaned the tank cap vent
-Checked the coils and caps
-Swapped to a fresh set of sparkplugs
-Adjusted the air screws
-Ran the bike without a filter and with the choke on separately
-Took off the carbs and did a through check and clean to make sure nothing was clogged
-Checked and readjusted valves
-Re-tightened cam chain tensioner
-Did a compression test, compression is still good (120-118 at cold crank)

There's only a small handful of things I've noticed that might be related, but I'm not sure if these are one-off issues or symptoms of the current problem. When I did a vacuum sync a short while back, cylinder one would misfire a smattering of times before normalizing. On top of that when I checked the fresh plugs after trying to run the bike, all the plugs were clean except cylinder one, which had some soot on it.

As it stands I'm stumped what else to check without opening the top end.

[scottly]

when I checked the fresh plugs after trying to run the bike, all the plugs were clean except cylinder one, which had some soot on it.

You have a problem with the #1 carb.

[TwoTired]

What brand and points and condenser?

[RAFster122s]

I am betting on the condenser being a diachi and it failed...

[TPIGroove]

What brand and points and condenser?

I'm uncertain, but they're from 4into1. What's the best way to test them?

[TwoTired]

What brand and points and condenser?

I'm uncertain, but they're from 4into1. What's the best way to test them?

My understanding is that 4into1 sells Diachi parts that have quality control issues.  Unless you have access to a capacitance checker, the alternative is to substitute a new or known good condenser to observe run differences.  Sometimes swapping from side to side will make the problem follow the part location.

[TPIGroove]

What brand and points and condenser?

I'm uncertain, but they're from 4into1. What's the best way to test them?

My understanding is that 4into1 sells Diachi parts that have quality control issues.  Unless you have access to a capacitance checker, the alternative is to substitute a new or known good condenser to observe run differences.  Sometimes swapping from side to side will make the problem follow the part location.

What would be the capacitance value of a good unit? On another note, does 4into1 have other poor electrical components? I got coils and points from them, too.

[TwoTired]

IIRC. .22 microfarads for the cap with stock coil inductance.  But, they have to withstand 400-ish volts back EMF from the coils without breakdown.  The latter is what usually makes them fail.

Diachi points have a poor reputation.  I've avoided them, using only TEC or Denso units.  I don't know about 4into1 coils.  Do they have a brand name or manufacturer name?  I think 4into1 doesn't make anything, just resell brands at a profit.

[RAFster122s]

Open your points cover in low light if it is a sparkling show beneath the cover at night on the cylinders that are misfiring you likely can be assured it is a failed condenser, provided the cylinder is firing...

[Deltarider]

A check of the 1+4 ignition would include:
Make sure none of the plugcaps and/or HT wires arc to the head. This is best detected by having the bike idle in the dark. All CB500/550s will suffer from this, sooner or later.
Replace a suspect sparkplug by a new one or switch #1 and #4 sparkplug to see if the problem follows.
Are both plugcaps firmly connected to their wires and are resistances correct?
In case you have the stock ignition, it wouldn't harm to have a look at the ignition plate to check for possible arcing of the 1+4 breakerpoints which could indicate a faulty condenser. Having said that, this would also have a negative effect on the #4 sparkplug. Anyway, this vid may be helpful.

At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner

[TPIGroove]

Alright, went into the garage and got the big 'ol box of parts (never throw away old parts unless you know they're broken). Dug out the old condensers that were originally on the bike, and I tested them with my ESR meter. No ESR, one had a capacitance of about .28uF and the other was at .246uF. I then took the two newer ones off of the bike, one tested at .22uF with no ESR, but the condenser hooked up to the 1-4 coil gave me a reading of just under .22uF and a whopping 18 ohms of resistance. Swapped the condensers with the originals, and the bike was able to idle with absolutely no issue whatsoever. At least I know I'm not going crazy.

Now, what's a good source for quality condensers? I'll use the old ones for now, but I'd rather hold them as backups.

[RAFster122s]

Use the old ones until you need new ones...no point throwing out or not using them...

[Deltarider]

[,,,] but the condenser hooked up to the 1-4 coil gave me a reading of just under 22uF and a whopping 18 ohms of resistance. [...]

With that your 1+4 points must have shown pitting.

Now, what's a good source for quality condensers? I'll use the old ones for now, but I'd rather hold them as backups.

If you look carefully, you'll find somewhere on your bike what brand it is. On mine more than just one spot. Could that be a clue where to order parts from?
What is ESR?

[TPIGroove]

[,,,] but the condenser hooked up to the 1-4 coil gave me a reading of just under 22uF and a whopping 18 ohms of resistance. [...]

With that your 1+4 points must have shown pitting.

Now, what's a good source for quality condensers? I'll use the old ones for now, but I'd rather hold them as backups.

If you look carefully, you'll find somewhere on your bike what brand it is. On mine more than just one spot. Could that be a clue where to order parts from?
What is ESR?

I actually forgot to put decimals in the right spots for the UF readings, oops. On top of that, I just did a reading for fun and the ESR was different, although still over 1 ohm. My tester has issues pulling readings from this one, only giving me a result sometimes, so there's definitely something wrong on the inside. ESR (equivalent series resistance) is just a capacitor's internal resistance, which should ideally not be there at all. The condenser is just a capacitor, but if it has internal resistance, it can't discharge the correct amount of energy.

As for purchase, I don't really know if honda dealerships will still be willing to get the parts for me. I suppose I could ask around, but an online source would be more helpful in the long run.

[RAFster122s]

South Sound Honda in Olympia WA has been a great source for lower prices on Honda, Suzuki and Polaris parts and their shipping costs are as economical as they can make them...
Highly recommend them.
I learned to avoid 4 into 1 for most stuff the hard way.....

[Kevin D]

I have replaced Daiichi condensers recently and they are the bargain condensers $7? a pair, instead of the genuine $25 a pair. There was a thread last week and a photo of the three petal flower Daiichi logo.
 When I have ohms checked a good condenser it goes to zero then climbs to infinity as it charges. Don’t give yourself a poke.
It has been said the proof is in the pudding, and the big blue spark at the 2-3 point led me to change that condenser and the bike ran like it was supposed to afterward, and no blue spark at the 2-3 point.
 Even the bad condenser passed the ensuing bench tests including 1000vdc megger. I might have put it in the oven for a bit then repeated the bench test but it’s in the trash.
These days I carry a pair of spare condensers with the spare fuses.

[TPIGroove]

I have replaced Daiichi condensers recently and they are the bargain condensers $7? a pair, instead of the genuine $25 a pair. There was a thread last week and a photo of the three petal flower Daiichi logo.
 When I have ohms checked a good condenser it goes to zero then climbs to infinity as it charges. Don’t give yourself a poke.
It has been said the proof is in the pudding, and the big blue spark at the 2-3 point led me to change that condenser and the bike ran like it was supposed to afterward, and no blue spark at the 2-3 point.
 Even the bad condenser passed the ensuing bench tests including 1000vdc megger. I might have put it in the oven for a bit then repeated the bench test but it’s in the trash.
These days I carry a pair of spare condensers with the spare fuses.

I'm still looking around for a good pair. There's a place near-ish me in Washington, MO that supposedly has OEM honda units, but they're charging about $45 for a single one.