Order of spark plug wires incorrect?

[seestheday]

Hi,
I was reading the FSM and noticed that the order that the spark plugs should be hooked up from left to right off the coils is 1,4,2,3 (page 233 of 442).

I will have to go home and triple check, but I'm pretty sure that the PO had mine hooked up 1,3,2,4.  

I personally put about 3K on the bike with it set up like this.  

Have I (and the PO) done serious damage to the engine because of this?

I suspect that it will run a lot smoother once I set them up correctly.

I thought to check because just finished adjusting my cam chain tensioner and checking my valve shims (they were all within tolerance).  I had to pull the spark plug wires to remove the camshaft cover and wrote down the order I pulled the wires off.  I was curious as to why it just wasn't 1,2,3,4 so I looked it up in the FSM and found the discrepancy.

[LukeM]

If memory serves, one coil fires for cylinders 1 and 4, and the other for cylinders 2 and 3.  When the piston is at TDC for the power stroke, the coil fires, and the spark for the other cylinder fires during the exhaust stroke.  Wasted spark, simpler operation, no need for distributor.

So, a firing order of 1-2-3-4 would not make sense, as the coil would not recover quickly enough to fire #3 after #2, and for #1 after #4.  Plus, I think cylinders 1 and 4 are offset 180 degrees from cylinders 2 and 3 on the crankshaft ( like a twin, only doubled ).  That's why they can fire like they do.

My guess would be 1-3-4-2 or 1-2-4-3.  And to answer the other question, yes, if your wires are misconnected, then it SHOULD run quite a bit smoother, and your mileage and performance SHOULD improve.

Luke M

[shinyribs]

Luke is right, 1&4 come up together and so do 2&3.The firing order would have to jump from one pair to the other,whichever that may be.Luke ,you said it best when you said its like a twin,only doubled.Four plugs but they fire two coils together so its not 4 independent sparks,but two sets of two


You mentioned valve shims,so you have a DOHC.I only have a little experience with my SOHC but im assuming they are set up the same as far as ignition and firing order go.For starters,whatever is in the FSM is probably correct,though typos DO happen.But 1 &4 fire off one coil and 2&3 off the other,but they fire together,whether on the exhaust or compression stroke.As long as you have the 2/3 coil going to the 2/3 cylinders,and likewise for 1/4.Then its good.If you reverse the 2/3 wires o the 2/3 coil there will be no difference.Its just two wires hanging off the same end of the same coil.Same for the 1/4 coil.    Or did I miss the question completely?Because if you take the 2/3 coil and put one of those wires on cylinder 1 or 4, I would imagine that would be beyond a smoothness factor.That should create a misfire and a dead cylinder at the same time.Two cylinders dead on a four cylinder engine will be 100% noticeable.Noticable,but unless it shook itself apart i dont think it will create serious engine damage.

[seestheday]

Hi Guys, sorry I wasn't clear in my post.  I completely understand why it isn't 1,2,3,4 after reading the FSM.  No questions about that.

I know that it is supposed to be 1,4,2,3 (going by the FSM).  What happened was that the PO put one of the 3 from the 2/3 coil onto spot 4 fromt he 1/4 coil - which is the switch that shiny mentions.

When I was riding it there weren't constant misfires and I recall checking for dead cylinders using the spit test on the headers (they all sizzled becuse they were hot - and got hot fast).

Maybe I'm being an idiot and am just confused, because from shiny's description the bike would have run at est very rough if this indeed was happening.  I'll double check tonight.

[shinyribs]

Sees,it is all conjecture on my part.I'm sure you are not an idiot.Take my advice with at least 4 grains of salt

[TOOLS1]

I doubt it would run if they were switched. Two dead cylinders are a lot to pull.
TOOLS

[Lucky 1]

The Honda CB750 has a firing order of 1,2,4,3  but each time #2 fires #3 fires also.
When #1 fires #4 fires also.
Every time the engine turns 360º one set of points fire.

Very unusual engine.
What that does is to burn unburned gases in the combustion chamber of the cylinders not on their compression stroke.

It does not matter if #2 and 3 or if 1 and 4 plug wires are mixed up because those plug wires come from the same coil. It will still fire  2 and 3 at the same time (same coil) and 1 and 4 at the same time (same coil).

Go to http://www.salocal.com/sohc/tech/tech.htm and CLICK ON "Firing Order" middle of page.
If you watch close you can see the blue combustion chamber fill and empty and the all red combustion chamber fill and empty on the compression stroke.

Side note: By having this firing order the CB750 engine was better balanced and it keeps pollution lower.
               At the 1977  Tokyo world motor show in Los Angeles,  Honda re-designd the cylinder heads on a 327 chevy v-8 engine to meet modern pollution standards WITHOUT a catalytic converter!

[seestheday]

Thanks for the link lucky and thanks everyone for all of the replies.  I'm sure I must have written down the order incorrectly or am just confused, I'll double check tonight.

Lucky - very cool graphic on that link.  Great visualization of how it burns unburned gases at the end of the exhaust/start of the intake stroke.

It also really clears up what is going on with the engine.

[Peterwh]

I think 1,4,2,3 is the same as  1,3,2,4.  It doesn't matter.  Providing the first number is 1 or 2, the second number is 3 or 4, the third number is 1 or 2 and the fourth number is 3 or 4 it will work fine.

Referring to an earlier post in this thread, I think you will find the points fire every time the crankshaft rotates through 180 degrees, not 360.

[Re-run]

Do not worry about firing order, it does not matter 1 bit. This system is quite common in older bikes so don't let that fool you. All you need to do is find out which coil fire which cylinders, nothing more. Once you have that, you take the 2 leads from it and plug them onto the spark plugs, it does not matter which order as the both fire anyways. It is called a "wasted" spark system.

For example, on my 78, while sitting on the bike, the right coil fires 1 & 4, the left fires 2 & 3.
I therefore take the leads from the right coil and hook them up to 1 & 4 in any order. Same with the left coil.

That's it, you are done.

As for emissions, I don't know, BUT if your engine is tuned properly, emissions are not much of an issue. So I would not worry about things burning on the exhaust stroke.

[Lucky 1]

Please go back and look at the flash file on that link that I posted
 and you will see that each set of points fire every 360º.

But you are correct in that when I said,"Every time the engine turns 360º one set of points fire. ",
I should have said, "Everytime the engine turns 360º BOTH sets of points will fire."

My mistake.