What would cause 2 and 3 to not fire?

[FastCletus]

Still cant get bike running right.  working on carbs and on stand it runs nice.  get it on street and barely moves.  Came in a checked compression  (see other post) checked plugs  1 and 4 were white on plug end, and 2 and 3 were oily.  I have firing order as 1 4 2 3.  Can 1 coil just go out?  

[TOOLS1]

"Can one coil just go out?" Yes!
TOOLS

[icerigger]

FSM says the firing order is 1-2-4-3. Try checking the wiring on the right side coil.

[TOOLS1]

As long as 1-4 are on one coil, and 2-3 are on the other your good. No need to worry about firing order.
TOOLS

[FastCletus]

Bike has never run that great, but I bought it non running so I hav never really known if its normal or not.  What are the odds this bike has always run on 3 cylinders and finally the coil just let go completely?

[shinyribs]

I'd say 50/50. Anything's possible. Usually when these bikes (at least the SOHC's,I imagine the DOHC's would be similar)are down a cylinder they have almost NO power and they run very rough. They'll shake like they're out of balance. They really rely on all four pulses to balance out,without it they shake and make all sort of bad noises.

[icerigger]

Also be a good idea to check the spark units behind the battery. Make sure they're wired up and grounded well. The FSM has a simple procedure for checking them.

[LukeM]

Actually, this engine operates like a twin, where two pistons move at the same time, just 180 degrees out of phase.  When one piston fires (top of compression/start of power stroke), the other one has finished its exhaust stroke and begins the intake phase). Honda did this so they could use dual coils, and not have to use a distributor.

I would trust the FSM as far as firing order and stuff.

My DOHC 750 had a bad #4 for a while, and it rode like it was down on power (which it was). It still ran OK, just no really good pickup.

Luke M

[FastCletus]

checked coil and it is listing 2.4 ohm on multimeter.  to my knowledge thats too low.  correct?

[FastCletus]

New coil is 40-60. since I am already this far. Think I should switch to dynatek.  If so which one for a cb750 dohc 1980

[Lucky 1]

First I would get a timing light ,clip it onto each spark plug wire, one at a time, and see if the coils are firing.
Otherwise get PROOF that the coil is not working.

OR if you want to take #2 or#3 spark plug wire  and plug a extra spark plug onto it and ground it to the cylinder head take your hand off of it and see if it fires.

IF the extra spark plug does fire then remove the spark plug from one of the cylinders that is not firing(cold exhaust tube), and check the gap.

Coils very rarely ever fail.

[shinyribs]

Correct Luke,they are 180 degrees out. Not a staggered crank setup like some of the high winding modern I-4's. But pull any one plug wire off an otherwise perfectly healthy bike and try to ride it. It'll turn into a glorious turd.SOHC,at least. Apparently the DOHC's are less responsive to it.

I lost a cylinder (plugged needle) one day and was only ~3 miles from home. Barely pulled the hill to my house.

[FastCletus]

New coil and carb tool should arrive today.  Hoping it will be a plug an purr exchange.  Maybe a little of carb adjustment.  Tired of looking at my baby on the lift and not under then sun

[FastCletus]

Coil Didn't arrive today, so I thought i would tinker a bit more.  Here is what I have determined

I swapped coils from drivers left side (the side that worked, cylinders 1 and 4) to the other side.  Guess what cylinders 1 and 4 still fire fine, but cylinders 2 and 3 still wont fire.  So that tells me that coil is not the issue.  I checked coil is getting power by checking yellow wire and black white wire with volt meter with engine on.  Dont really know how to work volt meter but I think with engine running it says 18-19

I think this is all thats holding me back from riding this weekend

[FastCletus]

BTW I pulled spark wire and checked against head with another plug, and no spark

[FastCletus]

Power 18-19volts going to coil for cyl 2 and 3.
checked plugs to make sure not fouled
swapped plug wires to see if wires were faulty
even swapped coil wires to see if i wrote #'s down wrong. nope

[Piute]

     Since you swapped everything else have you tryed swapping con.& points
     What can it hurt right needing to check mine (gap)is why it came to mind

[shinyribs]

18-19 volts seems awfully high. DOHC's have CDI boxes,right? Is it possible the overly high voltage took out a box?

[FastCletus]

Am I an idiot (wait don't answer that)  I didn't think my bike had points? I followed shop manual regarding ignition and I seem to think that this issue might be beyond my pay grade.  I hate electrics

My new coil should arrive today, I cant think that it will remedy the issue, but I will try nonetheless.

What would cause engine to just all of a sudden produce too much electrical power.  The bike ran fine prior to changing plug wires?

[Piute]

            Well it probably don't ,SEE there's your prob.
          Shiny corrected me,I have a s.o.h.c.(ya-no a real bike)SORRY about any confusion.
          Damn computer Modulars (electronic bull box).had 1 go bad on my H.D. got full of water.
                                   Will you just get it right