Cold Cylinders 2&4 totally stuck

[VB_cb750]

1980 CB750
I have two cold cylinders, 2&4. 2 plug is dry and looks like it’s not getting spark, looks completely unused. 4 is wet but not firing. Looks like the PO wired the coils directly to the battery through a relay. Not sure thats stock but seems odd.

1. Carbs have been cleaned and have fuel both in bowls and the intakes. The two center seem to have a little bit less fuel in the intakes
2. Checked vacuum with carb sync and all carbs are close to 5-10lbs
3. Valves have been set and are in spec
4. Timing has been checks, no chain slip
5. Spark units units have been checked by swapping them around
6. Pod filters but have been upjetted 10 higher for primary and secondary. Needle shimmed up
7. Compression is good in all 4
8. Spark looks good across all 4, even swapped out the 2&4 coil

Any direction? Looks like a may have 2 issues spark and fuel?

 

[VB_cb750]

Stupid question if I'm looking down at the coils which wire goes to where? Maybe the PO switched them around.

 

[dirtdigger]

cylinder pairing is cylinder 1 & 4 share coil and 2 & 3 share coil. you mentioned swapping out the 2 & 4 coil which is either a typo or you have plug wires going to wrong cylinders. If a plug is dry it is either firing or not getting fuel to that cylinder, if its wet its not getting spark, has low compression or is flooding.

 

[VB_cb750]

Might be a typo. Here is what I have sitting on the bike

Left Coil (1) to cylinder #1
Left Coil (2) to cylinder #3
Basically the two outside cylinders

Right Coil (3) to cylinder #2
Right Coil (4) to cylinder #4
Two inside cylinders

Thats with the assumed cylinder order of 1,2,4,3

 

[pidjones]

But, Honda numbers them 1,2,3,4.

Might be a typo. Here is what I have sitting on the bike

Left Coil (1) to cylinder #1
Left Coil (2) to cylinder #3
Basically the two outside cylinders

Right Coil (3) to cylinder #2
Right Coil (4) to cylinder #4
Two inside cylinders

Thats with the assumed cylinder order of 1,2,4,3

 

[dirtdigger]

looking from the top cylinder left to right is numbered 1234. firing order is 1243 though it really doesnt matter because coil (1,2) goes to cylinders 1 And 4 and coil (3,4) goes to cylinder 2 &3 so going by the previous post not sure what you are saying exactly think you are confused by the cylinder number. put the left coil to the two outside cylinders(1,4) and the right coil to inside cylinders (2,3)

 

[VB_cb750]

looking from the top cylinder left to right is numbered 1234. firing order is 1243 though it really doesnt matter because coil (1,2) goes to cylinders 1 And 4 and coil (3,4) goes to cylinder 2 &3 so going by the previous post not sure what you are saying exactly think you are confused by the cylinder number. put the left coil to the two outside cylinders(1,4) and the right coil to inside cylinders (2,3)

Yep. I think we are all on the same page. That’s what I got.

 

[dirtdigger]

Might be a typo. Here is what I have sitting on the bike

Left Coil (1) to cylinder #1
Left Coil (2) to cylinder #3
Basically the two outside cylinders

Right Coil (3) to cylinder #2
Right Coil (4) to cylinder #4
Two inside cylinders

Thats with the assumed cylinder order of 1,2,4,3

you said above you had left coil on cylinder 1, and 3 and right coil on 2 and 4, which isnt right. maybe take a picture would help clear things up?

 

[VB_cb750]

Here you go

 

[pidjones]

Here you go

View attachment 8717

That looks right.

 

[VB_cb750]

Yeah I tested the spark again with an inline steamer this time and everything looked good. Went back into the carbs, everything clean. Odd thing was one of the diaphragms with the needle didn’t come down as fast as the others. The needle had some scale and so did diaphragm causing it to bind slightly. Quick buff and now the cylinders all seems to fire. Who would have thought. Now it’s time for the break down of the bike and then rebuild