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Author Topic: CB400F only running on 1 & 4  (Read 204 times)

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Offline jakec

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CB400F only running on 1 & 4
« on: October 06, 2018, 02:33:58 pm »
Been riding my 400 daily for about 6 months. I knew the carbs needed a rebuild but haven't yet because it's my daily and it's been running fine. Yesterday I was riding in light rain and it started bogging down about 1 mile from home. I parked it and was supposed to ride about 40-50 miles today. I did some checks in morning to see if anything had gotten wet that would have caused the bogging in rain but no evidence.

I checked my plugs just for the heck of it, last time I checked was a couple months ago and they were all coffee. Now, they're like this:

1: coffee even though this is the carb that leaks
2: dry fouled
3: wet fouled
4: wet fouled

SO I'm like #$%* better start it up and see what happens. And it's knocking like crazy so I know it's running on less than all cylinders. I try a few times and it definitely 2 & 3 which are cold. I get new plugs and trim my leads and I have a healthy blue spark on all 4 plugs. I also noted that the coils are for 1 & 3 and 2 & 4 which contradicts what I've seen in other posts on the forum. I checked my manual and this is correct.

I know my delivery system is perfect because I've redone it all while I've had the bike. But I strongly suspect that the carbs are pretty bad inside, but up until now it was still running (I thought) pretty well. I'm convinced it's a carb issue so they will be coming off. I guess I'm just wondering how 2 & could go cold simultaneously like that?
1975 CB400F
1972 CL175 K2

Offline Scott S

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Re: CB400F only running on 1 & 4
« Reply #1 on: October 06, 2018, 02:48:37 pm »
 2&3 share the same points/ignition system. While your carbs may very well need work, look at the ignition system.
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Online calj737

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Re: CB400F only running on 1 & 4
« Reply #2 on: October 06, 2018, 02:59:48 pm »
Make dead certain that your coils are running plug wires to cylinders 1&4 from one coil, and to 2&3 from the other coil. And make sure the condensers are in good working order.
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Offline Deltarider

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Re: CB400F only running on 1 & 4
« Reply #3 on: October 07, 2018, 03:55:10 am »
Rain is often the cause of what you describe. HTleads are openly exposed to it and so can loose their capacity to transport the energy needed for a good spark. The diagnosis is often complicated when the bike, after some time, performs well again. Now the wires may be dry, but there could still be mineral residues that will act as parasites and in a next shower the problem may reoccur. So step one is to carefully clean the HTleads with some alcohol or a water displacer like WD-40. Another possible 'rain' cause could be a missing or damaged gasket under the points cover. (A mist of) Water will find its way in there and can cause misfiring. BTW, that water will also remove the grease from the cam exposing the breakerpoints heels to premature wear. The above inspections are very easy to do. Remember: 9 out of 10 carburetion problems turn out to be of electrical nature...  Hence my hesitation to go into the carb section at this stage. In case water has managed to find its way into the carbs however, I'd start with simply draining the float bowls. It takes a tiny often hanging drop of water to mess up carburetion...
Some CB550K3 owners have reported problems with the vent tubes, transporting water mist into the float chambers. Shortening the tubes with an inch or two is the remedy.
« Last Edit: October 07, 2018, 03:59:20 am by Deltarider »
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Online calj737

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Re: CB400F only running on 1 & 4
« Reply #4 on: October 07, 2018, 04:54:41 am »
I also noted that the coils are for 1 & 3 and 2 & 4 which contradicts what I've seen in other posts on the forum.
This is NOT correct. Its 1/4 & 2/3. You are misreading your manual. Fix this and your bike will run heaps better. Has nothing to do with rain.
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Offline Deltarider

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Re: CB400F only running on 1 & 4
« Reply #5 on: October 07, 2018, 09:00:56 am »
Been riding my 400 daily for about 6 months .... Yesterday I was riding in light rain and it started bogging down about 1 mile from home.
This is what I read about the beginning of the problems. Wrongly connected plug wires could never have produced a daily rider that in the words of the owner has 'been running fine', now could it?
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Offline jgger

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Re: CB400F only running on 1 & 4
« Reply #6 on: October 07, 2018, 09:14:11 am »
Delta you are correct about the water issues, but...........................here is what Calj is talking about from the op: I get new plugs and trim my leads and I have a healthy blue spark on all 4 plugs. I also noted that the coils are for 1 & 3 and 2 & 4 which contradicts what I've seen in other posts on the forum. I checked my manual and this is correct.

He may have corrected the electrical issue and now has the plug wires in the wrong place.

Offline TwoTired

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Re: CB400F only running on 1 & 4
« Reply #7 on: October 07, 2018, 09:28:11 am »
If your coil wires have no cracks, and the water seals/boots at each end (coil too) are intact, the engine will run fine with the leads drenched in water.  I've tested this personally.
If you get water under the points cover through a bad points cover seal, water will short/bridge the points  gap and prevent sparking/spark timing.

I made a neoprene gasket for the points cover so I could ride in the rain or splash through standing water without the engine misfiring.  The gasket is also reusable, so you only have to make one per bike.

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Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #8 on: October 07, 2018, 09:38:14 am »
I appreciate your responses guys. I should clarify that the rain I was in was very light, when I get home I always wipe down the bike and this time there wasn't even anough water on the bike to justify grabbing the towel. I did check the points cover though and the cork gasket is toast. However the points were very dry and there was still grease on the cam lobe.

As for the leads, all I can say is I've been riding with the as is for months?? Also I can confirm that the manual shows them routed the way that I have them. The coils are stock (TEC) and have he leads labeled 1,2,3,4. The caps are also shaped differently for the inner and out cylinders. Tonight I will post a photo of my set up as well as the manual which shows the routing.

Is it a 180* non- wasted spark system? If so I don't see how it could run at all with the leads swapped.
1975 CB400F
1972 CL175 K2

Online calj737

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Re: CB400F only running on 1 & 4
« Reply #9 on: October 07, 2018, 10:37:07 am »
It will run if you plug the wires into the coils incorrectly. It will produce the plugs you describe because your spark is occurring at the wrong time.

Install the wires as they shuold be:1/4 from one coil, 2/3 from the other. Then go ride. I’ll bet you discover a wholly different bike.

Your SOHC 400 has exactly the same ignition timing and setup as every other 350F, 500/550/650/750 made before 1978. And they all run quite well with an airbox in light rain... ::)
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Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #10 on: October 07, 2018, 11:09:34 am »
Ok I feel pretty silly but you guys were of course correct, it is 1&4 and 2&3. I think that I just assumed 1&3 and 2&4 would be the way the cylinders fired but had nothing backing it up. In any case, the wires are plugged in correctly and always have been. So, unfortunately it seems that I won't be discovering a whole new bike :( and that isn't causing my current problem.

« Last Edit: October 07, 2018, 11:13:44 am by jakec »
1975 CB400F
1972 CL175 K2

Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #11 on: October 07, 2018, 11:18:27 am »
I also noticed that while I have been doing these starts, when the bike dies the starter clutch makes a loud ZIPPP! Noise as it stops the crank. I don't remember hearing this unless I used electric start ( I always kick start unless I am sitting at a green light or something). Not sure if this is relevant but it has been very noticeable as I have been starting it a lot and having it die while trying to diagnose this issue.
1975 CB400F
1972 CL175 K2

Online calj737

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Re: CB400F only running on 1 & 4
« Reply #12 on: October 07, 2018, 11:22:47 am »
Now that the ignition is sorted out, check that the bowls are getting nearly the same amount of fuel. Most conclusive method is the Clear Tube method. This will allow you to verify the exact fuel height within each carb. It should be 3-4mm below the seam of the bowl.
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Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #13 on: October 07, 2018, 11:54:58 am »
Unfortunately the drain screws are all completely stuck - and I don't have a tool that would let me open the bowls while the carbs are on. So if we have it narrowed down to a likely carb issue then I think I'll have to take them off. I read another post here where a guy had the same problem and the press in jets had fallen out on the cold cylinders.
1975 CB400F
1972 CL175 K2

Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #14 on: October 10, 2018, 09:27:25 am »
I pulled the carbs last night. interior of the float chambers looked pretty clean. #2 & 3's bowls had the most red dust, but not a lot. All 4 hinge pins were replaced with trimmed length of a paperclip. And #1 was missing the butterfly spring.

All really weird and the sign of a shoddy rebuild. But what really surprised me was this:



1975 CB400F
1972 CL175 K2

Offline Don R

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Re: CB400F only running on 1 & 4
« Reply #15 on: October 10, 2018, 10:58:47 am »
 The paper clips will change the float operation for sure. Dang, that was some nasty fuel. Maybe someone here has a set of carbs reasonable.
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Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #16 on: October 10, 2018, 11:10:14 am »
Is the corrosion from sitting with fuel? All of the jet ports seem to be in fine condition, it's just the exterior that is chewed away like you can see in the photos. I think if I'm careful when installing the hinge pins I won't break anything.. do you really think I should consider new carbs?
1975 CB400F
1972 CL175 K2

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Re: CB400F only running on 1 & 4
« Reply #17 on: October 10, 2018, 12:54:22 pm »
Cant tell from the pictures, did you bump out the emulsion tubes too? Now is the time to do it while they're off the bike and stripped down. Careful, careful, careful with the force.

Worst case for your carbs, send them down to Jim French in GA (I think). He does micro welding and can restore the posts to nearly perfect condition. Cheaper and a better guarantee than a used eBay set.
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Offline jakec

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Re: CB400F only running on 1 & 4
« Reply #18 on: October 10, 2018, 01:32:17 pm »
One of the emulsion tubes fell out on it's own, the other three are still in there but move around freely. I haven't disassembled the top end yet so I haven't tried bumping them out from the top. My main worry is the hinge pin post.

Most of the carbs had a tiny bit of seepage, with #1 being the worst, I don't know what was different about it other than the fact that it was missing the leaf spring. The corrosion gets progressively worse from #1-4 with 4 being the worst. Hopefully I can reassemble with a real hinge pin without damage, if not I will look into repair.
1975 CB400F
1972 CL175 K2

 

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