Topic: New Member - 1978 CB550 carb sync issue. Lean now, and #2 cyl not firing.

[Calvin]

Thanks. Also no gasoline or gas smell on #2

[Calvin]

So I just got done pulling the slow jets and main jets out and the pilot needle. I use my air compressor to clean out everything and made sure that the slow jets especially were clear and put it back together. Still no fire on #2 at idle.

To recap, I know that I have fuel in the bowls, I have new spark plugs and there is spark coming from that plug and wire at least for sure there is a solid bright blue spark when I pull the plug put while the bike is idling and the other 3 cylinders were running, then ground that plug on the frame I can see it sparking repeatedly.

Was kind of banking on that to fix it actually I thought those jets may have been clogged from the symptoms.

I am now thinking either need those valves adjusted to make sure I have the best compression possible without a rebuild or possibly an electrical coil problem seeing how #2 and #3 plugs look considerably lighter and less fired than #1 #4, maybe it is possible that that coil isn't producing a good enough spark to fire all the time.

EDIT: pulling #3 doesn't seem to change my idle either. It think I hear the rpm drop a small amount but if I pull either #1 or #4 the bike stalls immediately. #2 or #3 won't stall the bike at idle. Starting to really look at the coil now...

At idle, pulling plug wire to #2 is the only one that will cause the idle to drop. It's hard to tell whether or not it is firing while riding or not. There is a lot of stuttering right around 1/3 rpm while idling if I am basically give the bike just enough throttle to maintain speed. I either downshift so that my rpms and throttle are a little higher and it feels pretty good then, but possibly still not firing.

Any help guys  ?

[calj737]

Use a meter and test the coil.

[Calvin]

Use a meter and test the coil.

So basically just measure the resistance of the secondary coil by measure the resistance between the #2 and #3 plug wires?

[calj737]

And the primary.

[Calvin]

Coil #1/#4:

Primary resistance: 4.9 Ohm
Secondary resistance: 27.1 k Ohm

Coil #2/#3:

Primary resistance: 1.2 Ohm   
Secondary resistance:24.8 k Ohm


Thanks calj737.... looks like I found an issue here....

In your experience with a bad coil as low as 1.2 Ohms, would you expect it to fire at all?  Or is that just a shot in the dark?

Either way, it looks like I will probably just upgrade as a package and get the Dyna-S ignition with their 5 ohm coils.


I feel like if it was firing, then it would have been killing the sh*t out of my battery with such low resistance it should have been pulling 4x the current as the other coil.

[DaveBarbier]

You can swap the coils and see if the issue moves to the 1/4.

[jonda500]

You can swap the coils and see if the issue moves to the 1/4.

I see this suggested a lot in here, but I'd love to know how you do this if you have oem coils as the #2.3 coils' leads aren't long enough to use as a #1.4 coil? 
I sure wish honda had made the spark plug leads longer - on one of my bikes I've had to trim the #3 & #4 leads so much to get a good connection to the plug caps that they just barely reach the plugs now.
John

[Calvin]

Ok, I could try that tomorrow but like jonda500 said, I really dont think those leads are long enough to swap from 2/3 to 1/4.

Quick question, do cylinders 1 and 4 fire at the exact same time?  I thought so based on the wiring schematic of the contact/breaker points assembly it seemed the at as the one point makes contact it applies voltage to one coil which then fires 2 plugs at the same time.  Is this correct?  I question because I was told differently by somebody.

Also, does anybody have an experience with a coil with low resistance?  I have seen posts stating that if the coil resistance is too HIGH or if there is no continuity, but I haven't seen anything mentioning low resistance.  I am wondering because I know I could physically see spark on plugs from #2 and #3 but I am betting that they are breaking down under load and not firing.  I would assume that with such low resistance it would have issues.  I know people have issues with 3 ohm coils and I'm running on a 1 ohm coil...

[jonda500]

Yes, the coils supply a spark to both 1 & 4 (or 2 & 3) simultaneously every revolution.
John

[calj737]

Yes, the coils supply a spark to both 1 & 4 (or 2 & 3) simultaneously every revolution.
John

The definition of a wasted spark system. Many vintage 4 cylinder bikes use this.

[scottly]

Coil #1/#4:

Primary resistance: 4.9 Ohm
Secondary resistance: 27.1 k Ohm

Coil #2/#3:

Primary resistance: 1.2 Ohm   
Secondary resistance:24.8 k Ohm


Thanks calj737.... looks like I found an issue here....

In your experience with a bad coil as low as 1.2 Ohms, would you expect it to fire at all?  Or is that just a shot in the dark?

Either way, it looks like I will probably just upgrade as a package and get the Dyna-S ignition with their 5 ohm coils.


I feel like if it was firing, then it would have been killing the sh*t out of my battery with such low resistance it should have been pulling 4x the current as the other coil.

1.2 ohms is too low. Was this test done with both primary coil wires disconnected? Do you have stock coils? Touch the leads of your meter together and see what it reads.

[Calvin]

This test was done measuring the two primary wires right at the coil with the caps still on the spark plugs. They are the stock coils. The resistance between my meter leads alone is only.2 ohms so I am sure I got an accurate reading. It's a very high quality meter also.

Should I be testing the primary restaurants any different way or at a different place?

[scottly]

Check for a short between the primary wires outside of the coil body.

[scottly]

You are measuring the primary resistance with the primary coil wires disconnected from the harness, correct?

[DaveBarbier]

You can swap the coils and see if the issue moves to the 1/4.

I see this suggested a lot in here, but I'd love to know how you do this if you have oem coils as the #2.3 coils' leads aren't long enough to use as a #1.4 coil? 
I sure wish honda had made the spark plug leads longer - on one of my bikes I've had to trim the #3 & #4 leads so much to get a good connection to the plug caps that they just barely reach the plugs now.
John

Hmm, you got me, haha. It's a logical test that I guess isn't able to be performed. I'll have to go out to my bike and have a look. I've never actually done this test before, haven't had a need.

[Calvin]

So unless there is something blatantly that I am missing here, it should not matter whether the harness is connected or not when measuring the primary coil resistance.  I am measuring it directly at the wires that go into and out of the coil, as seen on the diagram below. 

It is just resistance, as long as there is no continuity between the points other than through the coil (the positive battery terminal is not shorted to the frame), it is just going to measure the least resistance between the two test leads.

I would also assume I got a good reading because the other coil was 4.9 ohms, measured the same way.  My meter resistance between leads is .2 ohms so if we want to get technical and subtract that it would be 4.7 ohms, nothing some dyna coils shouldnt fix! 



Let me know if there is any reason measuring this coil here while connected should make any difference.  Thanks!

[scottly]

So unless there is something blatantly that I am missing here, it should not matter whether the harness is connected or not when measuring the primary coil resistance.

What you are missing are the points: if you measure the primary resistance on a connected coil whose points are closed, you are also measuring the resistances of the regulator and field coil, oil pressure lamp, etc in parallel. The measured resistance is much lower than even a good coil, isolated from the harness.

[Calvin]

Im sorry but I still have no idea how something on either side of the meter leads could have an effect on the resistance reading as long as they are not shorted. The meter is going to send current from one lead to the other and the current will take the path of least resistance.

A resistance reading should be un affected by anything in the circuit that is in series on either side of the test points. I agree if I those things were in parallel to the two points where I measured from, that It would cause a lower reading .

Sounds like I am going to have to disconnect the coil and measure this because it's still bothering me lol.

[Calvin]

Well damn. You are completely right scottly. I realized the kill switch was off and so I turned it on to disconnect that circuit and each coil was 4.5 ohms. Guess it is true that rarely do coils go bad.

Sorry I am stubborn and sometimes I just need to see it to believe it 

What else could the problem be ignition related?  I still feel ignition may be the culprit, or maybe electrical.

Any suggestions?

[calj737]

Thanks. Also no gasoline or gas smell on #2

Well you have ruled out ignition, how about you return to the "ole fuel delivery" issue sine your post indicates you have none.

[Calvin]

I am just not sure where to even start with fuel delivery. The bowls are all full and level, I cleaned out the inside of the carbs and all the jets and emulsion tubes. They looked fine. So there's gas in the bowl, nothing in the jet. And the compression I thought would be good enough to have a good vacuum to pull the fuel up through the jets.

Did I rule out all of the ignition system by just checking the coil resistance?

[calj737]

Your issue didn't change when you swapped the plug wires, so that tells me your ignition is very likely fine. If I recall from your original post, points, plugs and condensers are new. So with your coils testing good via Ohms, I'd say the fact that at idle, your #2 plug is dry and does not smell of gas, you have a fuel delivery issue. Is it vacuum related? Compression related? I don't think so, I still believe your idle circuit is clogged. I lean toward that based upon your statement that above 1/2 throttle, the bike wakes up and runs well. That indicates the Main and Needle are involved and delivering fuel.

Unless I'm wrong...

[flybox1]

I still believe your idle circuit is clogged. I lean toward that based upon your statement that above 1/2 throttle, the bike wakes up and runs well. That indicates the Main and Needle are involved and delivering fuel.

^^^ Yuup

... it seems that #2 cylinder is not firing, at least not at idle.  When I open it up, it feels fast and I believe that they are all firing.

^^^ an indication (to me anyways) there is something preventing gas flow in the idle/pilot jet circuit in that carb.
When you 'open it up' you involve your needle jet/main jet in supplying fuel to your engine.

[Calvin]

Your issue didn't change when you swapped the plug wires, so that tells me your ignition is very likely fine. If I recall from your original post, points, plugs and condensers are new. So with your coils testing good via Ohms, I'd say the fact that at idle, your #2 plug is dry and does not smell of gas, you have a fuel delivery issue. Is it vacuum related? Compression related? I don't think so, I still believe your idle circuit is clogged. I lean toward that based upon your statement that above 1/2 throttle, the bike wakes up and runs well. That indicates the Main and Needle are involved and delivering fuel.

Unless I'm wrong...

Couple things.

1.  When I have the kill switch on and crank the starter a few times to get fuel into the cylinder and pull the plugs,  none of the plugs have fuel on them, this is not exclusive to cylinder 2.

2.  I can see daylight through all the idle jets and when I cleaned them and reinstalled them, I did not keep track of order so it's likely there is a different jet in it now than there originally was, and the problem did not change.

3.  I only swapped coils 2 and 3 with each other. And those are the two problem cylinders. I have not swapped wires from 2 and 3, to numbers 1 and 4, and vice versa. That would probably tell me the issue but the wires won't reach.

4. If it was ignition related, couldn't it have something to do with the lower voltage at idle due to the charging system?  When revving it up the battery voltage rises. It seems to me right now it will either fire on cylinder 2, or cylinder 3 at idle. Never both, but 1 and 4 are always firing.

I am just pointing towards ignition now because I have taken the carbs apart a few times now and made sure the jets were clear. As recent as Sunday, and I blew 80psi of air through all of them and I watched fuel spray out of the slow jets when I did that.