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Discussion Starter #1
Hi all,
So I bought a -88 shadow with -95 engine. I wasn’t able to test the bike too much when I bought it and now that I had the possibility, I realized that it wasn’t running right. I got the engine running a little bit better with new spark plugs, but my problem is that the 2 cylinder (front?) doesn’t seem to be running as it should.

my concern, and the question really, is that how should the wasted spark ignition work here? I can unplug one or both of the spark caps on the right side without any effect to running. If I have the right side plugged or unplugged and unplug the spark plug from front cylinder (2?) on the left side, the motor runs nicely with only cylinder number 1. However, if I would do the opposite and unplug cylinder number 1 (rear) on the left side, the motor dies. I can get it to run though, if I increase the throttle.

is it possible that the engine runs with only one coil (left side coil) and therefore it runs badly, because only cylinder 1 is timed correctly. I have tested coils and cables and switched them together and nothing changes. I have tested that the primary side gets signal, but I haven’t checked any timings yet.

I am sorry if my English is horrible. I am a Finnish guy.

Edit:

Someone wrote this on this forum and this really confused me, since I have one coil connected to both cylinders.

"
Wasted spark typically fires two separate spark plugs on two separate cylinders.
Wasted spark systems are used because they are cheap to manufacturer,
work relatively well, and have few parts to go bad.
The Shadow's do have a wasted spark system, but they fire both plugs on the
same cylinder at the same time. This is done for a more complete combustion.
Honda is not the first to do this, Nissan has done this for many years on their automobiles.

"
 

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1995 VT1100C2
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If you are getting good spark both sides and coil tests OK, it is likely one of your carburetors is gummed up and I would either try running some Seafoam (carb cleaner) or dismantling and cleaning the carbs. How does it run with choke on or off?

G.
 

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Discussion Starter #3
Right, I'll try that. It sure runs better with choke on, but I have to try if it does the same kind of misfiring or what ever that is that is happening. I am fairly sure that carburetors are in a need for some cleaning, but I am still wondering why the other coil doesn't seem to do anything
 

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1983 Honda vt750 Shadow
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The waste spark system on these bike fires 2 plugs on the same cylinder at the same time.
It sounds like the front cylinder is weak from fuel or vacuum leak problems, or weak ignition. Try spraying around the carb boot with carb spray to see f it changes the idle sound.
Another thing is to spray water on the coils and wires when it is running to see if there are any arcs from bad wires or coils.
Run it up at 2000 RPM for a minute and then take all the spark plugs out to see the color. Are they wet, or too white ?
 

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Discussion Starter #6
Mine is wired like in the attached picture. Is it wrong then or is Honda using both wasted spark and twin spark?

To clarify: mine is wired so that the leftmost coil is for both cylinders on the left side, and rightmost coil is for both cylinders on the right side. Nothing happens or changes if I disconnect both spark caps on the right side when the machine is running. Even the sounds doesn’t change at all.
 

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First don't pull the spark plug high tension leads with a bare hand while the engine is running. Next Stop the engine, remove 1 spark plug and connect it to a high tension lead. Put an old spark plug in the spark plug hole (so no fuel vapor can escape and blow you up.) Lay the spark plug threads on the engine. Crank the engine and look for good blue spark. Easiest in a dark garage. Test each spark plug like this remember: put an old spark plug in the hole.

If you are not getting a spark, switch coils and try the same.

Next, your wiring diagram is unusual. VT1100 1995 has a front ignition coil and a rear ignition coil. Front is on the right side. On each coil the high tension leads run right side of coil to right side spark plug, Left side of the coil to left side spark plug. However 1988 I don't know. 1987 through 1996 there were 2 ignition pulse generators, one for each cylinder. These produce a voltage to the ICM, to the coils, and tp spark. That way you don't adjust timing but just replace failed parts.

1585426091545.png
 

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Discussion Starter #8
I tested each spark plug that way and everything was working. The method in that video was for the clarity of the unusual behavior. As I have been trying to say is that everything works fine, coils, spark plugs etc, but my concern is why nothing changes when I disconnect the cables from the right side and start the engine. But if you are indeed correct on the coil connection setup, then it would mean that mine is connected complete wrong. I wonder how it could be even working then and how did the PO drive it in the first place?
 

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Set the plug wires so each coil fires 2 plugs on only one cylinder. Since the system fires on each revolution of the crank that may be why it is able to run with spark any time the mixture is in the cylinder under compression. Crazy idea .

I think I saw where Harley and maybe others use one coil to fire different cylinders, like a car with waste spark. But not these bikes.

Here is a diagram from 1985-1998 Haynes manual (which is so-so at times) for 1995, but may help with the colors of the trigger wires for each coil.1988 has the same colors.
 

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Unless this is a completely custom ignition system, I would connect coils as per the diagrams provided. Front ignition coil to front cylinder. Rear ignition coil to rear cylinder. Not sure why it was working but interesting
 

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Discussion Starter #11
If you are getting good spark both sides and coil tests OK, it is likely one of your carburetors is gummed up and I would either try running some Seafoam (carb cleaner) or dismantling and cleaning the carbs. How does it run with choke on or off?

G.
Here's a test with choke on completely, video
Here's without choke, video2
 

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Discussion Starter #12
The waste spark system on these bike fires 2 plugs on the same cylinder at the same time.
It sounds like the front cylinder is weak from fuel or vacuum leak problems, or weak ignition. Try spraying around the carb boot with carb spray to see f it changes the idle sound.
Another thing is to spray water on the coils and wires when it is running to see if there are any arcs from bad wires or coils.
Run it up at 2000 RPM for a minute and then take all the spark plugs out to see the color. Are they wet, or too white ?
Here's a picture of one of the spark plugs. All of them looked the same.
285814
 

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Discussion Starter #13
Set the plug wires so each coil fires 2 plugs on only one cylinder. Since the system fires on each revolution of the crank that may be why it is able to run with spark any time the mixture is in the cylinder under compression. Crazy idea .

I think I saw where Harley and maybe others use one coil to fire different cylinders, like a car with waste spark. But not these bikes.

Here is a diagram from 1985-1998 Haynes manual (which is so-so at times) for 1995, but may help with the colors of the trigger wires for each coil.1988 has the same colors.
Today I tested this. I took both coils out and wired them so that they match your drawing. With this setup, only cylinder 1 worked. Cylinder 2 misfired very loudly. The cables were also cut so that they wouldn't have enough length to be wired like that in the first place. (see attached picture)

After that I tried another test. I took one of the coils out completely and tested how the motor would run with only one coil.

I connected coil 1 secondary side to left side of the machine, so that another high tension cable went to cylinder 1 and the other to cylinder 2. Primary side was connected to Black/White and Yellow/Blue. Motor ran "fine". It ran but just like in the previous videos, but that is most likely due to carburetor or mixture problem. I did the same test with the other coil with the same result.

After that I swapped the high tension cables to the right side of the machine and tested with both coils so that the primary side was now connected to Black/White and Blue/Yellow .. Nothing.. Motor didn't run. It did misfire a bit, but didn't start. Plugs gave spark though.

Then, and this is interesting, I tried the same thing again but now with Black/White and Yellow/Blue and the motor ran nicely again.

So, to me, this proves that the wiring is correct (mine is wired EXACTLY like in the attached picture), but the "coil 2" primary side doesn't work as it should. Could it be timing or something else? It does give spark though.

I will continue this tomorrow with an oscilloscope and try to figure out the timing and the signal levels.

285815





285816
 

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Discussion Starter #14
Oh, and the PO had obviously tried to fix this because the spark generator unit was opened and the taped back together. Nothing on the circuit board was touched though. I checked the connection from the unit to coils and the resistance to cam pulse generator. Everything was fine.
 

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Hi Swifty,

As far as I know, this bike should not be firing front and rear spark plugs right side from one coil and then firing both front and rear spark plugs from left side. Can it even do that modified? My understanding is we have a front coil firing both front plugs and a rear coil firing both rear plugs.

In the photo of his coils, looking at his front coil (on the right) the high tension leads are reversed but that should not matter.

When he pulls the left rear high tension lead the bike stops which indicates that is the only spark happening on the correct stroke. Right rear is likely sparking but on the wrong stroke.
 

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Discussion Starter #16
Anyway,

this is how the ignition fires. This is measured from the primary sides, so that the red line is coil 1 on the left (YELLOW / BLUE).

285882


also, now that I run the motor a while with everything put back together as they were. I could hear a misfire here and there and after a while both front cylinder plugs were black.

285883


so my take on this is that ignition is working somewhat as it was meant to, but I just don’t understand the idea of the other coil firing that much late. The real problem with the engine must be related to the carburetor, and likely to diaphragms, since the PO just mentioned that they were in bad condition. This would explain the excess fuel in cylinder 2 and black ignition plugs, right?

I will take the carburetor apart this week.
 

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It looks rich in general but the front plugs are too much for sure. Maybe a high float level even.
I am no expert in which years are single pin and twin pin offset motors. My 1983 is an offset pin crank and the coils are fired staggered like that, with 2 pulse generators controlling the firing of the cylinders.And it fires on each revolution of the crank. Dual fire/dual spark .
 

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Discussion Starter #18 (Edited)
Thank you all for your help!
I took the carbs out and cleaned them. One jet was a bit plugged and one A/F valve was missing an o-ring. Other than that everything was fine. This, however, had no effect at all.

here’s how the motor sounds. What do you make of this?

 

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Discussion Starter #19
I opened the crankcase cover to see if the pulse generator is okay and found out that the pulse plate is actually from the -88 engine, not from the -95.

286214

1988 pulser is like this.

286212

1995 pulser is like this.

I suppose the pickups are aligned correctly, because you can't change the orientation, so the timing should remain the same. I changed the plate and then connected the coils as they should be connected. Coil 1 both spark plugs to cylinder 1(rear) etc. I fired up the engine and realized that cylinder 1 runs perfectly, but cylinder 2 misfires and almost doesn't run at all. The engine actually got a lot worse. This made me wonder if the person who mounted the new engine actually didn't ever get it to run and then just played with the ignition until it ran somehow and sold the whole thing. The person who sold this bike to me said (eventually) that he never actually got the bike working, even after multiple attempts to clean or adjust the carbs, because he thought that it would be the problem.

I checked the engine label and it says: SC32E-2005980, which to me tells that this should be 1995 VT1000C2 ACE engine and the old one was 1988 VT1000C. What is the real difference with these engines, because I suspect that this is indeed a timing issue, which could come from wrong ICM, but did they make it any different between those models? I tried to check the timing with a timing light today, but the engine blows so much oil out from the timing hole that I couldn't read the marks.
 

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Surprised you found an 88 IPG. I would have thought that with the 1995 engine, the PO would have left the 95 IPG in place. So my guess is all the ignition is 1988.

You will have to cross reference the wiring harness but the actual differences between 88 and 95 ignition are IPG, ICM (part number difference), harness and coils (resistance). Perhaps find a Haynes manual that covers all those years and you can get it to work.

G.
 
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