Ignition issue, new GS owner, first time old bike owner.

[Guest]

Oh boy oh boy, I finally got the cafe racer of my dreams, it's a beautiful 79 GS750...had her for 2 weeks and we were enjoying our time together and then all of a sudden smooth idle went to CRAP chunky idle, backfiring, etc.

Made it to work, park'd her up, felt the headers 2 & 3 cold..booo.

Read up and found out how our coil setup works. She has an electronic ignition, but had the standard coils.

So I ordered some Dyna DC1-1 with new plug wires. Being my first ever old bike, and first ever ignition debug....I felt good when I saw that the LEFT coil (1 4) was original equipment, however the RIGHT coil (2 3 not working) was some aftermarket job.

I have no idea when that was put on or by whom.

I put on the Dynas, and cranked her up, and the good news is she started....but the bad news is that 2 and 3 are STILL cold as ice.

Before I ship her off to a pro, does anyone in the great GS Cabal have any ideas of something "simple" to look at in terms of things that send electricity/information to JUST the RIGHT coil?

I don't pretend to know how a full electrical ignition works, have a rough idea, and my guess is that the "magic box" is what is controlling the coils upstream. I doubt there is a fuse or anything JUST for that coil...not sure.

Any info would be greatly appreciated, I miss her already and we just started dating. :-)

Thanks
Eric

p.s. tomorrow I'll pull of a plug wire for 2 and 3 and see if I can get it to arc to the engine......I believe all I need to do is just pull it and put the electrode close. Is it possible that 2 and 3 are just needing a throat clearing from having been ridden a bit with them not firing...fuel etc...backed up in the carb..? totally guessing....I was SO sure it was the coil...it made so much sense.

[fastbysuzuki]

Try taking off the plug caps on the offending cylinders remove plugs, put plugs back in the caps hold by the insulated part touch the threaded part on the plugs (one at a time) on cylinder fins ignition on and press starter you should get a Bunson blue coloured spark at the plugs and a loud crack as the spark jumps the plug gap.

[matt1100]

Check voltage coming into the coils. With the engine off, key on, kill switch in run, and spark plug wires removed (and maybe the plugs too); rotate the crank like your doing a valve adjustment. When it rolls to the trigger spot for cyl 2,3 you should get voltage similar to battery output on the terminals going into the coil, I think.

Your "magic box" may have **** the bed and you may want to consider a dyna-s.

Good luck

[erics75218]

great responses, I'm going to do the spark test tonight.

Unfortunately, my ability to do this work is limited due to knowledge and tools.

And I fully confess to not understanding this ignition system....I believe it's Dyna S.

I need to make sure both coils are getting 12V...but as I said the wiring is a bit CUSTOM *cough* so I don't really have the orange/white wire setup as easy to define. I think the orange/white is spliced into 2 yellow now :-).

Am I right in thinking that each coil has 3 connections (not counting plug wires).

Power - in my case I believe it's orange/white feeding yellow, this wire should come from "the back of the bike where the battery is"

Signal - in my case it's black on one side, blue on the other, connecting to white I believe...and this connection should becoming from the "points", which are electronic now.

Ground - in my case is purple, connecting to the mounting posts.

IF I get spark on cyl 4 AND 3 tonight (I'll check with the plug from 4 on both, since maybe the plug in 3 is now fouled from running with no spark for a bit?) then it's maybe fouled plugs

IF i get no spark on 3 using plug from 4. Then I was thinking of jumping the 12v wire directly from the left working coil to the right coil to assure me that it is in fact, getting power...since 1 4 work fine. IF that works, then I know in the hacked wiring, there is an issue. (I have no voltage tester..:-/)

IF that still doesn't work, then it's something wrong with signal, and beyond my ability and I'll take her to a shop where they have high tech tools like 12v testers and such. :-)

Thanks a bunch guys....and feel free to laugh or poke fun I wont take offense, as I said I'm new to this type of thing. I just got setup here and have almost no tools and such, it blows.

I've attached a picture of the old gal, she's a looker and I need her back on the road, summer is coming...even in London!

[2BRacing]

Nice looking bike you got there!

Maybe there are some other members in your area who could help you, instead of taking the bike to a shop. Most often the shops don't want to work on the old bikes.

There is a UK Facebook page for GSR members, so introduce yourself on there as well and hopefully there will be someone close to you who has the tools etc. to help you.

Good luck!

[Spiff]

Three? I have a 78 GS750 and coils on that bike only have two wires, one is power (orange/white) and the other is ground(white for left coil, black for right). Ground wires black and white are connected directly to the points, or in your case the dyna replacement which grounds the coils at 180degree intervalls triggering the coil and thus firing the plug. It's really simple.
The dyna ignition has a red wire too, this is a power feed to the magnetic pickups on the dyna, it connects to the power feed to the coils(O/W) OR another source of switched 12V. but if something was wrong with this then the engine wouldn't fire at all.

Here you can see the dynatek wiring scheme:

http://www.powercommander.com/downloads/Support-Released/Dynatek/Manuals/DS3-1_3-2.pdf

If someone has hacked up the wiring, then it might be a bad connection to the coil(s).

[erics75218]

Three? I have a 78 GS750 and coils on that bike only have two wires, one is power (orange/white) and the other is ground(white for left coil, black for right). Ground wires black and white are connected directly to the points, or in your case the dyna replacement which grounds the coils at 180degree intervalls triggering the coil and thus firing the plug. It's really simple.
The dyna ignition has a red wire too, this is a power feed to the magnetic pickups on the dyna, it connects to the power feed to the coils(O/W) OR another source of switched 12V. but if something was wrong with this then the engine wouldn't fire at all.

Here you can see the dynatek wiring scheme:

http://www.powercommander.com/downloads/Support-Released/Dynatek/Manuals/DS3-1_3-2.pdf

If someone has hacked up the wiring, then it might be a bad connection to the coil(s).

This is great info, from memory while at work, I believe this is what I'm seeing on my setup. I do have 3 wires each for sure...the 2 you talk about, orange/white battery, white and black from dyna....but then 2 purple going to the post.

I'm also going to pull the plug wires off, and swap the black and white wires...putting the one from the coil that's not firing on the one that currently is, and see if it fires. If it doesn't, then something is up with that wire / "points" thing

Great info, I really appreciate it!

The rotor that goes in place of the points, again not sure how it ACTUALLY works, but does it have seperate 1/4 and 2/3 pickups on the rotor? It'd be strange for one of those to go off. I'm putting my eggs in the no 12V power...or bad connection somewhere.

Under my seat, there is a magic box.....out of this box

[Spiff]

Not quite sure what I'm looking at in the last picture

But yeah try and swap the black and white wires around, if the problem follows the black wire then it's a problem with the dyna most likely.
How does your sparkplugs look? Are all sparkplugs working? I.e firing...

[Spiff]

Here you see the stock points setup on a GS.

https://www.youtube.com/watch?v=YIFTrwtfxus

The rotor is connected to the crankshaft and spins with it, the rotor has a little cam on it which pushes on the points to make them open and close at certain intervalls, in this case every 180degrees of rotation. Imagine the workings of the camshaft and valves on the head opening and closing.
There is one point for each coil.
The dyna s system replaces the cam with a rotor that has a little magnet on it and the points are replaced with a magnetic pickup.
The little magnet on the rotor is like the cam lobe on the old points system, it passes the pickups every 180degrees and triggers the pickups like the old cam lobe would trigger(lift) the points.

Hope this made some sense

Here is a guy doing the switch from points to dyna: https://www.youtube.com/watch?v=wWl3g1XMMb4

[OldVet66]

The violet and yellow wire are the only necessary wires in the picture of the coil. It looks as if someone attempted to ground the center mounting point of the coil with the black wire. It is not necessary. Trace it back and see if it is a ground wire. The 12V+ to both coils come from the same orange/white wire in the original wiring. The other two are ground. Since you have replaced the coils with the Dyna green coils + and - is marked and that shouldn't be a problem to check out. That leaves a trigger module to check out. After you sort it out, you might want to consider the coil relay mod so you don't have to rely on a possibly reduced voltage coming through the kill switch to feed the coils with the orange/white wire. That orange/white wire would then be used to close the relay contact (voltage drop would not matter) and feed fused 12V+ directly from the battery to the coils. If it is a bad trigger module and is a Dyna-S, Dyna will sell you a new module plate for cost if you call them and get a RMA number and return the old module plate for testing. Might save you a few bucks. It should be somewhere in the $75.00 price range.

[erics75218]

Just to clarify on the photo as it's somewhat hard to see. We're looking down from the front of the bike on the coil that was no longer firing.

The violet wire is connected to the post and I'm not exactly sure it's origin
The black wire (from rotor) to one contact on the coil
The yellow wire (from orange/white) to the opposite coil

In the Coil instructions, they say the dual coils have no polarity so it doesn't matter which way it's hooked up.

[OldVet66]

The picture is a little hard to see. As long as you know the source of the wires that is not a problem. You are correct about the Dyna instructions. I just looked at a spare set of mine and they are not marked + -. Just for grins I would still put the 12V+ opposite the spark plug wire terminal like the single coils. Reversing the wiring still might determine if the plug fires from the center or ground electrode of the spark plug and you want it firing from the ceramic insulated center. At least hook them up with the + the same on both coils.

[erics75218]

Update

Ok I got a plug checker and a multimeter and went down and did some more poking around. I think I may have found the culprit of woes, but I need ya'll to guide me :-)

A confirmation of wiring:
OrangeWhite goes to power both coils through a yellow wire each
Each coil, voltage checked, is getting very close to 12V

Each coil has a purple wire at the post, maybe this isn't needed but don't think it's harming anything, I'm assuming this is ground.

Out of DynaS
Black wire goes to right coil via connector that also has some red wire split off and this red wire goes somewhere in a big wrap of cables. I checked this voltage with ignition on and it's reading around 10 volts at the contact point on the coil, as well as before and after the connector.

White wire goes to left coil via a connector. I checked this voltage with ignition on and it's reading around 1.2 volts both at the contact point on the coil, as well as before and after the connector.

I have no idea if I'm checking those voltages right or if it's even relevant, I just wanted to check for symmetry. I was putting the negative probe on the post, which I assume is ground, and the positive on the contact point of the DynaS wire on the coil. I checked these voltages a few times after turning the engine over and what not, trying to make sure that it wasn't "parking" the points in the same spot..maybe it would flip flop the voltages the other way, not sure if this voltage is "showing" me the on/off of the distributor.

With this setup I checked for spark on all 4 plugs, as before 1 and 4 are hot, 2 and 3 are cold.

I switched around the Black and White wires, Black to Left coil, White to Right coil and tested for spark again. This time 2 and 3 are hot, and 1 and 4 are cold.

So this tells me, someone who knows nothing, that the wiring to both coils is ok in terms of power as both coils seem capable of producing spark. For some reason, the black wire coming out of the DynaS has more voltage than the white one and seems to do nothing.

I poped open the cover where the points were, and there was in fact a DynaS thing, first time I've seen that so that's good! Nothing was dangling off it, everything looked ok, but there are really no parts to it really, so I don't know where to go from here.

Was my method of diagnosis stupid?
Did I come to the right conclusion?
Does a simple looking device like the DynaS really fail that much?
Why did one DynaS wire have 10 volts, and the other have just 1.2?

What do ya'll think?

[posplayr]

This is great info, from memory while at work, I believe this is what I'm seeing on my setup. I do have 3 wires each for sure...the 2 you talk about, orange/white battery, white and black from dyna....but then 2 purple going to the post.

I'm also going to pull the plug wires off, and swap the black and white wires...putting the one from the coil that's not firing on the one that currently is, and see if it fires. If it doesn't, then something is up with that wire / "points" thing

Great info, I really appreciate it!

The rotor that goes in place of the points, again not sure how it ACTUALLY works, but does it have seperate 1/4 and 2/3 pickups on the rotor? It'd be strange for one of those to go off. I'm putting my eggs in the no 12V power...or bad connection somewhere.

Under my seat, there is a magic box.....out of this box

Based on that picture I would say someone abhorred soldering or really did not do a good job on the electrical up to par with the rest of the bike.

If there is more of that you might want to get some quality crimper (they are not too expensive) and some open barrel crimps and crimp, solder, shrink tube connections that look like that one. Get some Deoxit spray as well and us it on all connections.

There are a few other, but Vintage connections have an excellent crimper for the money ( I bough two)

RTL Crimping Tool

http://vintageconnections.com/

[Spiff]

With this setup I checked for spark on all 4 plugs, as before 1 and 4 are hot, 2 and 3 are cold.

I switched around the Black and White wires, Black to Left coil, White to Right coil and tested for spark again. This time 2 and 3 are hot, and 1 and 4 are cold.

So that tells you that BOTH your coils are working. Good!

Your problem then lies in the path of the signal going from the dyna s to the coil. Either something is wrong with the black wire, or something is wrong with the red wire going to the pickup with the black wire.

I read dyna s has a 1 year warranty, how old is you unit?
Might be worth contacting Dynatek about this, maybe you can get a new one by sending in yours.