Topic: Ignition coil issues with my 78 CB750k

[78texas750]

At least I think it is ignition coil issues. My bike has been acting weird since last night. Cylinders 1 and 4 are not running like they should. they will kick on and off while I am trying to accelerate and will not really run while at speed or while idling. I had this same problem a couple of weeks ago and check through the carbs, so I am 95% sure they are not the issue. When I had the problem last time I couldn't figured out exactly what the problem was, but it started running fine again after I unplugged the 1-4 coil to check them and plugged them back in. I assumed that the problem was just the coil disconnecting while I was riding, but now I have made sure the connection is good and the problem persists.

What should I check next?

[Stev-o]

Welcome. I would check all wiring connections next.   Coils rarely go bad.

I also have a K8, where in TX are you?

[78texas750]

Thanks! I'm near Dallas normally, but I'm actually in Boston for the summer. I have check the wires, but can't find where the problem is. It seems to run fine until I actually take off and get to the end of the road then the problem starts

[Spanner 1]

Loose black/white wire @ coil connection ( sorry , it's under the tank  ); loose wire @ 1-4 point, bad condenser @ 1-4....... check that 

[TwoTired]

When was last 3000 miles tuneup check list performed?  Might be a point's related problem corrected with proper adjustment.

[78texas750]

Loose black/white wire @ coil connection ( sorry , it's under the tank  ); loose wire @ 1-4 point, bad condenser @ 1-4....... check that 

I check the black/white wire under the tank and it is connect as it should be.

When was last 3000 miles tuneup check list performed?  Might be a point's related problem corrected with proper adjustment.

I'm not sure when the last time the points were check since I just bought the bike a little over a month ago. I will check that today.

If the timing is off would that cause 1 and 4 to not be running at all? When I run the bike, or try to at least, it is only running on 2 and 3. The pipes for 1 and 4 are completely cold while the other two are hot like they should be

[TwoTired]

I'm not sure when the last time the points were check since I just bought the bike a little over a month ago. I will check that today.

If the timing is off would that cause 1 and 4 to not be running at all? When I run the bike, or try to at least, it is only running on 2 and 3. The pipes for 1 and 4 are completely cold while the other two are hot like they should be

There are two point sets.  One controls cylinders 1,4 and the other controls 2,3.  If the point set for 1,4 isn't working, cylinders 1,4 will be cold.
I can't say that it IS your bike's problem.  But, with the information given us, it could be and should be addressed as it is part of basic maintenance for the machine that keeps it running on all four.

Routine maintenance is what helps keep major maintenance at bay.  Check the simple things first. A loose point screw, or point contact surface contamination can prevent cylinder function.

[bollingball]

78texas  All thing mentioned so far are pointing you in the right direction. Have you downloaded the factory service manual from here ? When first getting one of these bikes forget anything the guy you bought it from (PO) told you was done as far as maintenance. You cannot even trust most of the shops. If they cannot plug a laptop in it they are lost. It does sound like this could be in the points area of the bike. Look for a loose wire around the 1-4 points or maybe a wire touching ground that should not be. Start looking and post back. Welcome to the madness plenty of good people and help here.
Ken 750 K8

[BobbyR]

I too have a 78K. Check all of the things TT recommended. Then while you are down there I would suggest you follow the wires leading out of the points and along the frame. I had a wires wear through and short to the frame which caused 2 cylinders drop out on and off.   

[bollingball]

I know you said you checked the coils. But remember that black/white wire feeds one coil power then there is a short jumper that goes from one coil to the other coil I have had that come loose so one coil worked and the other did not. The print shows the yellow 2-3 coil fed first and the blue 1-4 fed by the jumper. See what I mean check for 12v+ on the 1-4 coil. Then if need be move to the points Good luck
Ken

[78texas750]

TwoTired - Thanks, I figured that was true, but thought it would hurt to ask to be sure that I wasn't just making things up in my head.

bollingball - Yes, I have the service manual that I downloaded from the forum here. I do typically ignore what the previous owner tells me about maintenance, but so far, as I have been searching though the bike, all of what the previous owner told me appears to be true. I will also check the jumper that goes from one coil to the other to be sure that is not the issue either.

BobbyR - I am thinking I may have a short now like you said. I check the points and everything appears to be good there. The points are nice and clean and the timing is set right.

[lucky]

Check to make sure the points are not arcing to ground on the cover. ride it without the points cover. You will have your answer.

It happens when a condenser has absorbed all the energy that it can, and needs to be replaced.

[78texas750]

Fixed!! It appears that it was the connection near the oil tank and the rear brake light spring

[BobbyR]

Fixed!! It appears that it was the connection near the oil tank and the rear brake light spring

Great news. Some problems just need a step by step analysis.

[Stev-o]

Good to hear. 

[bollingball]

Fixed!! It appears that it was the connection near the oil tank and the rear brake light spring

Good catch When I read that I said WTF I thought I had cleaned every connector on my bike. But I missed that one thanks for posting your find.
Ken

[78texas750]

Thank you all for your help!