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

[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

[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?

[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?

[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.

[flybox1]

#1 - Neither do mine, nor would I want to do this for an extended period of time.
#2 - reconfirm they are all stamped with a Keihin K, and are all the same size, AND, your emulsion tubes are just as clean as your pilot jets.
#3 - unlikely as your plug wires probably are not long enough.
#4 - . . .

Do you have a carb slide installed backwards, or have a really off bench sync? 
Can you hook up your vacuum sync tool and see whats happening?
Take a picture of the intake side of your carbs so we can see the intakes (choke plates open and slides down)

If the vacuum is really off on #2, it wont kick in until the slide starts moving.

[Calvin]

All the jets are the same size and stamped with the funny looking keihin k. I bought them brand new about a month ago.

The carb slide is installed correctly, because all of the adjuster nuts are facing up. When I did the carb sync with the dampers all of them were pulling the same vacuum when I was done, but the fluctuation of each gauge was way different, which I thought was due to cylinders not firing. 


I will tear them down again and get a lot more pictures of everything.

[Calvin]

So I just took the carbs off to take pictures, everything looked good, slides looked pretty even, jets all the same, then I started looking at the wires and I realized that if I stretched them to the limits I could swap 1/4 and 2/3, so I excitedly put the carbs back on to test swapping wires.

With the wires swapped, the bike didn't even start. I put the wires back where they go and started it up, ran fine. I started taking a video and pulling plug caps one by one to see the idle change when they were pulled. Pulling 1 or 4 killed the engine, then pulling 3 just dropped the idle but didn't kill the engine, then I pulled 2 and the idle actually dropped unlike every test before. So it seems all the were firing.

I put the air filters back on and hooked up the carb sync tool and did another carb sync. This time I had to raise the rpm to around 2500 for a steady idle because some cylinders still fluctuated too much like before, so I kept the idle higher for the sync. They were not perfect when I started so I had to make some small adjustments, I could hear the idle changing everytime I adjusted an individual carb. I got them all close and put it back together.

Bike seems to run pretty good now it doesn't have as much power around the high range, about 3/4 throttle and is still a little poppy with the d7ea plugs, but overall runs better than before. I am not sure why they are all firing right now.

I think i need to richen it up over all by adjusting the needle clip settings.

I still don't feel comfortable that out of nowhere it's firing again, I'd like to upgrade the ignition in the future still. I will update this again if this problem persists, about to go for a long ride!

Thanks everybody for the help. 

[Calvin]

I didnt confirm the needle because that requires individually  disassembling each carb which I did not do tonight. I just took the carb back off and took the caps and bowls off and the jets out.

And yes, last time I cleaned the jets (Sunday) I cleaned the emulsion tubes too.

I did not notice if all pipes were equally hot, they seemed to be.

Not sure about your field of play comment, I understand it, but I was not going to completely remove the throttle slide shafts and disassemble each carb to check the needle position as it has not changed since the bike was working fine. Also. Last time. Thoroughly cleaned the emulsion tubes.

I have read on here mostly that d7ea plug is recommended, should I run the dr7 instead?

[scottly]

Timing was ''just done" by the honda shop before I got it according to the PO.  I believe him, and I have only looked at the points to verify how the points looked because he said the points and condensers were just replace and timed by the honda shop, the points did look very new.  I believe the timing is good, I can check that last.

Have you checked the timing yet??

[DaveBarbier]

The carb rack does not need to be disassembled to adjust needle height. Open the top caps and with a small JIS driver unscrew the two screws holding the arm to the slide. Can actually be done with the carbs on the bike but it's a little cumbersome.

Regarding what Fly said about the slides being in wrong: On your PD46C carbs the slides can be installed with the angled cutaway facing the motor instead of the correct way which is facing the airbox. There is nothing to prevent this on these carbs, one just has to be mindful.

The slide adjuster nuts would always be facing up regardless if the slides were in correctly or 180° out.

Maybe take and post some good pictures of your carbs under the bowls of the jets and in the inlet mouths like Fly suggested. Could be something the old timers could point out that's incorrect.

[DaveBarbier]

Timing was ''just done" by the honda shop before I got it according to the PO.  I believe him, and I have only looked at the points to verify how the points looked because he said the points and condensers were just replace and timed by the honda shop, the points did look very new.  I believe the timing is good, I can check that last.

Have you checked the timing yet??

Agreed. As others have said it's such an easy thing to do it's stupid not to verify. Even if you're 100% sure the guy said it was done. All it takes is a test light and 5 minutes or your multimeter set to continuity if it has a beep.

[Calvin]

The carb rack does not need to be disassembled to adjust needle height. Open the top caps and with a small JIS driver unscrew the two screws holding the arm to the slide. Can actually be done with the carbs on the bike but it's a little cumbersome.

Regarding what Fly said about the slides being in wrong: On your PD46C carbs the slides can be installed with the angled cutaway facing the motor instead of the correct way which is facing the airbox. There is nothing to prevent this on these carbs, one just has to be mindful.

The slide adjuster nuts would always be facing up regardless if the slides were in correctly or 180° out.

Maybe take and post some good pictures of your carbs under the bowls of the jets and in the inlet mouths like Fly suggested. Could be something the old timers could point out that's incorrect.

No I have not checked the timing yet.  I will do that next.  Hopefully you guys can tell me if this looks right like your PD46C carbs!

Here is #s 1 and 2, the slide height looks pretty even, the choke butterfly valve works well when installed, no blockage



#s 3 and 4 (didnt have a great pic of all 4 slide height at the same time


All 4


Throttle slides (upside down?)  Haven't been changed since this issue started.



Carb #2 cylinder head side:  Had fuel on it just like all the other ones when removing.  Seems like fuel is getting into it.



Thoughts? 

DaveBarbier I will check the timing next with a test light.  I have the cover off  and can tell the points look very new, have not tested the timing yet, but I will check that shortly.

I think I will just individually disassemble each carb to get the needle settings, I am thinking going one clip setting richer.  Last disassembly the two screws at the bottom of the slide that need removed were on there very tight and I did not want to risk stripping them because there wasn't a problem before or a need for me to check.  Now with the new plugs its just a little bit poppy in the midrange.


Thanks for all the help once again guys.