1981 Cb750 only #2 cyclinder not firing

[evan_51]

So I am new to this form and have been searching for any solution to this problem.  I have been researching this for several days I am hoping someone out there is smarter than me.  Here goes;

1981 Cb 750 DOHC only cylinder #2 not firing also rough idle at 1k rpm (possible due to no fire)

I have spark on all four cylinders, along with four new NGK plug, boots and wires.
Compression on all cylinders are within 10psi of each other at 150ish
Battery is fully charged during testing
Timing is spot on all four cylinders
One coil is wired to cylinder 1&4 The other coil is wired 2&3
Swap plugs same effect
Swap wires and boots same effect
Swap coils same effect
swap wires to coil from igniter box and change the plug wires to right firing order same effect
Swap igniter boxes same effect
Exhaust pipe 1,3,4 about 450 degrees exhaust pipe 2 about 200 degrees

Carbs have been gone through 3,4,5 times
All jets sizes are the same on all four carbs
I have switched the air cut off valves from cylinder 2 to cylinder 1 same effect they are in good condition
When the cylinder 2 plug is pulled it is wet so it is getting fuel
All float levels at 15mm
Pilot screws all set to 1.5 turns then i tried 1.75 turns per manual
pilot screw then were set to 2 turns, 2.5 turns 3 turns same effect
Carbs have pod filters and have been switched to see if that effected anything
Tried also without any air filter
Carbs do not overflow with gas
Sprayed carb cleaner, brake clean, starter fluid, on all boots from carb to cylinder head to check for leak, no idle change, no leak

Lastly I snipped the wires from the igniter boxes to the coils, pulse generator, grounds, and soldered new wire encase of high resistance, open, or short. cylinder 2 still 200 degrees and the rest 450+
Continuity is found through pulse generator 2&3 and 1&4 about same Ohms

If any one can provide any info that would be great, web page on how the pulse generator works, inter diagram of igniter boxes, anything even if it is something stupid like did you have the choke on, or make sure the plugs are all screwed in.  And yes I checked that. Also extra info on the accelerator pump, and air cutoff valves would be great

[TOOLS1]

Have you taken it's temperature with the engine running at 1/2 throttle (4-5 K RPM)? I have had this same scenario happen to me. Just because the plug is wet does not mean that it is getting fuel at idle from the pilot circuit. Then when it is revved up it will pull from the main circuit, and it might catch, and run, or it might not, and just make the plug wet.
TOOLS

[LukeM]

Relocated this posting to a more appropriate location.

Also, that may be the best and most thorough description of a problem I've seen in a LONG while.  My compliments. One thing to check, since you've done just about everything else: look at the diaphragms inside the carbs. Hold them up to a strong light, and look for pinholes or cracks.  That little leak could cause problems, especially at idle.

Luke M

[MSUM8]

Hi Evan, did you ever find an answer to your problem?  
I am having the same issue on #1 and just cant figure it out.  I have run out of diagnostic tests to try and find the problem, so I would be very interested to know if you found the problem and how you fixed it.
Thanks.

[evan_51]

Right so I pushed this bike to the side for the last few months, and now the problem has fixed itself magically.  All cylinders fire.
 
A new problem though has arrived after looking at this yesterday.  Cylinder two and three are not timed right , yet 1&4 are spot on.  The info per-manual only talks about timing 1&4.
 
1981 Honda cb750 dohc.

A link to info about adjusting the timing other than what the manual says would be perfect.  And tools I think you were right about the idle circuit being messed up originally.  

[NickleNdime]

You ever figure this out I have the same thing going on .