Topic: CB 400/4 only running on 2 Cylinders

[SteveC]

 Hi, can anyone help me with my 1978 CB 400/4? I bought it as a box of bits. It's now all together but it's only running on 2 cylinders No 2 and No4 but when I swap the blue and yellow wires that come from the points it runs on No1 and No3 cylinders. So everything seems to be working just not all together. Any ideas would be appreciated cheers.


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[calj737]

One coil pairs cylinders 1&4, the other coil pairs 2&3. The Blue wire from your ignition feeds 1&4, Yellow feeds 2&3. So if all that is correctly wired up and paired up, most likely culprit is the points or condensers on your ignition plate.

Have you serviced/checked/set the points gap? Is the timing set properly?

[SteveC]

One coil pairs cylinders 1&4, the other coil pairs 2&3. The Blue wire from your ignition feeds 1&4, Yellow feeds 2&3. So if all that is correctly wired up and paired up, most likely culprit is the points or condensers on your ignition plate.

Have you serviced/checked/set the points gap? Is the timing set properly?

I've serviced and reset the points gap, they look to be in good condition. One of the condensers is new so I've tried swapping them around but that didn't make any difference. Do you think the timing could be out? The engine was a runner (or so I'm assured) before the previous owner removed the engine and all I've done is put it back into the frame.
Appreciate your help


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[calj737]

Well if you confirm you have spark on all four cylinders, and the pairing of the cylinders fires correctly, then an examination of your spark plugs is in order. Do they show signs of combustion? If they are clean and dry, then you likely have a fuel delivery issue (fuel level in the carbs). If they are dark and sooty, then you have a spark quality issue.

If they are dark and wet, you have too much fuel for the quality of spark. It could be a few things, but without further diagnosis and values posted (spark, fuel level, plug readings, cap resistance) we are speculating. But at least now you have some things to check and diagnose. 

[MoMo]

Confirm there is spark as Cal mentioned.  Either dirty points or the wire to points improperly installed if spark is missing

[SteveC]

Thanks for the info
The spark is good on all cylinders (checked when the plug is out). They are quite sooty though. I don't know if they are firing in the correct order but when it's running on 2 cylinders it's 1 cylinder from each coil


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[robvangulik]

From your description i still think you've got the spark plug leads mixed up, one coil for the outer cylinders and one coil for the inner two....

[Bodi]

"it's only running on 2 cylinders No 2 and No4 but when I swap the blue and yellow wires that come from the points it runs on No1 and No3 cylinders"
This seriously makes no sense. Reversing the coil wires shouldn't have any cylinder firing so that the engine would try and run.
I can't think of anything that could do this except - maybe - having the plug wires mixed up, with the 1-4 coil going to plugs #1 & #3 for example.
The points for 1-4 should fire at (close to) TDC on 1 & 4, BDC on 2 & 3. So connecting the wrong points set to a coil should absolutely not have any useful ignition... sometimes the fuel/air is ignited with the intake valve still open on the end of the intake stroke, firing a sweet flame out of the carb.
So reversed SOHC4 coil wires (not uncommon!) gives you no running, with bonus backfiring. Not "running on two cylinders"...

[SteveC]

From your description i still think you've got the spark plug leads mixed up, one coil for the outer cylinders and one coil for the inner two....

Thanks for the reply.

Looking down with no tank on, the left coil goes to the 2 cylinders on the left and the right coil goes to the right cylinders, this is the only way they will fit due to their lengths. Do you think this is wrong??


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[TwoTired]

Looking down with no tank on, the left coil goes to the 2 cylinders on the left and the right coil goes to the right cylinders, this is the only way they will fit due to their lengths. Do you think is wrong?

Most definately.  One coil should route to one and four the other to two and three cylinders.
Sounds like the 1/4 coil was changed out with another 2/3 coil.  That one has shorter leads.

Cheers,

[calj737]

Looking down with no tank on, the left coil goes to the 2 cylinders on the left and the right coil goes to the right cylinders, this is the only way they will fit due to their lengths. Do you think this is wrong??

Yes, this is wrong. The coil (pick one) with the BLUE wire should be running spark plug wires to the two outside cylinders (this is 1&4) and the other coil should have the Yellow wire running to it, and the plug wires running to the two interior cylinders (2&3).

With the tank off, seated on the bike, looking forward, cylinder 1 is left most, then 2, 3 and finally 4 moving left to right. This should help you correctly orient the ignition wires and plug wires.

[SteveC]

Looking down with no tank on, the left coil goes to the 2 cylinders on the left and the right coil goes to the right cylinders, this is the only way they will fit due to their lengths. Do you think this is wrong??

Yes, this is wrong. The coil (pick one) with the BLUE wire should be running spark plug wires to the two outside cylinders (this is 1&4) and the other coil should have the Yellow wire running to it, and the plug wires running to the two interior cylinders (2&3).

With the tank off, seated on the bike, looking forward, cylinder 1 is left most, then 2, 3 and finally 4 moving left to right. This should help you correctly orient the ignition wires and plug wires.

Thanks for all the replies I'll get some new leads (current ones are too short to swap positions)and give it a go


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[strynboen]

you can splice some new vire in the coils..try to go for coils and  new vire. for sohc- honda...on Google..

the idea is to machine in to the coils brass solder point..and solder a new vire on..and epoxy glue the hole..better then bay strange aftermarked coils..