Dyna S sapping voltage?

[Jim Cosenza]

Hi, I'm currently working on a 1977 Gs750. It's the first Suzuki I've owned, but not my first vintage bike by any means. I'm a Honda man at heart, but I was suprised at the power and smoothness this bike has over my '75 Cb750.
Anyway, to my question. I recently checked the voltage at my coils, and it measured 9.76 volts. The bike runs well, but I figured it might run better with the coil realy mod and a full 12 volts at the coils.
So I prepared to do the mod, and just for kicks, I checked the voltage at the coils with the Dyna S ignition unhooked( it is spliced into the stock coil feed wire, as per the instructions). With the Dyna unhooked, the coils got 12.37 volts. Hooked it back up, back down to 9.76. Has anyone had a Dyna sap voltage like this? Thanks, Jim

 

[salty_monk]

Not a Dyna but I've had a stock Ignitor sap power like that, turned out it was resistance in the main plug that runs to it. (I tried to use the same plug to power the DYna S with the same result so in the end I routed it a different way).

Dan

 

[Jim Cosenza]

Well the only power wire that leads to the Dyna is the one that connects to the coil's power lead, and it's giving a full 12v, until I connect the Dyna. Weird. Any idea on maybe another switched 12v source for the Dyna only? Thanks, Jim

 

[salty_monk]

If you put a relay in you can switch both from there. You can pull a switched live from several locations on the bike but I would think you have some kind of problem for the Dyna to be causing this.

How do you have it connected to the Orange White coild power lead? Is the Dyna new? Has the Dyna power wire been overheated at any time? (had that issue on a vehicle once before, was the resistance of the wire itself that was through the roof & causing the issue).

 

[posplayr]

Well the only power wire that leads to the Dyna is the one that connects to the coil's power lead, and it's giving a full 12v, until I connect the Dyna. Weird. Any idea on maybe another switched 12v source for the Dyna only? Thanks, Jim

From what you are describing, either your battery is dead of your Dyna=S is hosed. A relay will not help either.
The Dyna-S should pull very little current although I can't claim to have ever measured it. I would think it should be even less than a stock ignitor.

 

[Jim Cosenza]

The battery has 12.58 volts at the posts. The Dyna isn't new(it was already installed when I bought the bike). The bike seems to run great, except rich running down low, but that's because three of the four pilot fuel screws were over-tightened by the PO. I can't afford $20-30 a piece to get them in the rebuild, so I just ground the broken ends to a point and messed with the settings until it ran the best. But really, besides that it has good power and has performed well on numerous short, low-throttle trips and a few short, ramhousing type ones. The plugs are mostly black, but they still fire. I just though there might be some untapped potential, and the voltage drop still confuses me, but as long as it runs I guess I'll leave well-enough alone (although I don't like it). Oh yeah, anyone got any pilot fuel screws for cheap? Thanks, Jim

 

[salty_monk]

I think you can buy individually at www.z1enterprises.com

 

[posplayr]

The battery has 12.58 volts at the posts. The Dyna isn't new(it was already installed when I bought the bike).

Is that voltage at the battery whenthe Dyna is installed and the key on? And you still have 9.76V to the coils and Dyna.
or 12.37 to coils alone?

Bottom line is the voltage at the coils will drop because of bad connections upstream of the coils as the coils pull a fair amount of current. The Dyan should be almost nil as compared so something must be wrong for the DynaS to pull it further down.

 

[Guest]

Is the headlight on or off?

 

[Jim Cosenza]

When the key is on and the bike isn't running the battery post voltage slowly drops to 12.08 volts then stabilizes. The voltage to the (dyna 3ohm) coils is the same. The headlight is off. I put the bike back together today and rode it. It starts right up and runs well. I'll probably just continue to clean up any un-necessary splices, connections, etc in the wiring and periodically check the voltages to make sure this isn't a slowly worsening condition. I'm still open to suggestions on finding the cause, if anyone has an idea. Thanks, Jim

 

[salty_monk]

Check any connections from the Dyna S to the loom & also make sure the resistance of the wire leading from Loom to Dyna isn't sky high...

Other than that I'm out of ideas.

Dan

 

[posplayr]

Check any connections from the Dyna S to the loom & also make sure the resistance of the wire leading from Loom to Dyna isn't sky high...

Other than that I'm out of ideas.

Dan

Dan,
The issue with the apparent observations is that the voltage is dropping when the DynaS is attached.
Considering the 2 (3-5 ohm) coils should be pulling about 3 amps a piece when energizing, for there to be an even bigger load put on the battery to pull it to 10 volts you are talking close to a >1 ohm short.
This seems excessive, but I'm not there to double check the measurements.
Jim

 

[salty_monk]

Jim,

I understand but I had something similar on my 1000G once. Put the Ignitor plug (into the plug on the loom) or connect anything such as the Dyna S to the O/W switched live at the loom end of the igniter plug (resides behind the battery box) & it would pull the voltage down by a couple of volts.
I never fully understood it, what I did do was re-route the Dyna S to pick up it's power from elsewhere (relay for the coil mod from memory), block that plug on the loom for ignitor off (used the old plug with the contacts removed & opening epoxied over) & then it was fine.

Dan

 

[Jim Cosenza]

Checked voltage at Dyna with key on, approximately the same as coils(about 9.7V). Checked Dyna feed wire resistance, .6 ohms(the same as resistance at two points six inches apart on my Kerker). Checked voltage at the Dyna while running, 11.99 volts. I think that means I'm good? Jim

 

[posplayr]

Checked voltage at Dyna with key on, approximately the same as coils(about 9.7V). Checked Dyna feed wire resistance, .6 ohms(the same as resistance at two points six inches apart on my Kerker). Checked voltage at the Dyna while running, 11.99 volts. I think that means I'm good? Jim

Not clear what your voltages are (is 11.99 at idle or something else?)

At least your Dyna and Coils are reading the same thing now (tha tmakes more sense).

Sounds like you need a coil relay mod. My ED was a had start with 10V at the coils.

 

[posplayr]

Jim,

I understand but I had something similar on my 1000G once. Put the Ignitor plug (into the plug on the loom) or connect anything such as the Dyna S to the O/W switched live at the loom end of the igniter plug (resides behind the battery box) & it would pull the voltage down by a couple of volts.
I never fully understood it, what I did do was re-route the Dyna S to pick up it's power from elsewhere (relay for the coil mod from memory), block that plug on the loom for ignitor off (used the old plug with the contacts removed & opening epoxied over) & then it was fine.

Dan

Dan,
We may be talking about different situations but I would guess either and ignitor or a Dyna would only pull a few 100's of milliamps while a coil will pull 3 amps which is maybe 5-10 times that of the ignitor. Sure if you have a dirty lead supplying current to the ignitor it will get pulled down.

However if the there are also coils on the same lead, they are going to do most of the damage dropping the voltage. So a coil ignitor combination on the same circuit should always read the same.

Jim