Coil Problem?

[Guest]

Hey guys, new guy here with a problem. Imagine that. I have a running 1977 GS550 that I am tranforming into a cafe racer for my niece. In trying to improve the starting I began checking out the electrical system. I searched this section for information and I'm very pleased with how much I learned. Here are my findings: Voltage at battery 12.4. Voltage at coils 10.2. I tested voltage at various places along the hot (orange) lead up and through the starter button, down (orange/white) to (2 red) the Dyna S ignition, back up (1 white 1 black) to the coils. As long as I have everything connected I get 10.2 volts along the route. If I disconnect the coils I read 12.2 volts along the route. I performed an ohms test on the coils. Primary 4.4 ohms. Secondary 24.8k ohms. On the electrical odds n ends page Mr. Billy Ricks writes that 3-5 ohms is acceptable for the primary side. 30k to 50k ohms for stock secondary side. Can anyone troubleshoot my problem from this information. Oh yes, I have cut out all of the old connections and isolated the lead. If I have left out any information needed to make a educated decision let me know and I will provide it.

Thanks.

[tom203]

You probably want to do the coil relay mod (this improves voltage to coils) - the dyna might not like the drop that you got now.
But this is likely just one of many issues involving hard starting

[rgtrough]

Hey Tom, thanks for the reply. I am sure there are other issues with this 38 year old scooter, the electrical system just became my starting point. I am still baffled by the voltage drop. Will old coils cause the drop. I guess I will bite the bullet and replace them. They look as if they need to retire.

[JTGS850GL]

I wouldn't jump on replacing the coils yet. A 2.2V drop between the battery and the coils is too high. The coils are not out of spec and are not known as a high failure rate component on these bikes. If you can't identify where the voltage drop is occurring, then doing the relay mod will bypass the problem area and provide you with a good voltage at the coils. As identified by tom, you need to go through all the general maintenance first. Dirty carbs and tight valves will cause hard starting issues. Bite the bullet and do what's been needed for 30+ years.

[tom203]

Your coils are likely fine-it's the long winding path from battery to coils that causing the drop with the ignition coil energized. Mine has about same drop, but the stock ignitor doesn't seem to care.

[Brendan W]

A bad contact only drops volts if current is flowing. Somewhere in the ign supply there is a bad 'un. Have you checked the voltage at either side of the main fuse ( ign on) , the voltage at the return wire ( orange usually) from the ign switch and the voltage at either side of the 10A ign fuse.
The main suspects for me in a case like this are the ign switch itself, it's plug, the fuses and the connector from the fusebox to the harness.
Fuses, especially the glass ones can look ok but the solder joints inside crack. In some cases you will even feel one end of the fuse is warm.

[rgtrough]

Hey guys, again thanks for the replies. As I hoped to explain in the orginal post, I isolated all of the wires running upstream off of the orange wire. as long as the coils are connected I will have voltage drop after a 3 wire connector in the headlight. Downstream from this connector, no voltage drop even with the the coils connected. I cut out the connector wired straight through, still voltage drop at coils. dissconnect coils no voltage drop. Voltage remains steady at 12.2 all the way through system even with coils connected until after the transition from o to o/w in the kill switch. Both sides of the fuse, both sides of the starter relay. I am happy to hear that you all feel that the coils test ok. I did also. I ran a jumper from the battery directly too the coils. (Relay for dummies). Of course 12.4 volts at coil engine fires much better. I will be installing the coil relay mod today (Sat.). I will post results. One question, is there any benefit to running a larger gauge wire from the relay to the coils?
Again thanks for the help.

[posplayr]

The problems are all in connectors and switches. There is no reason to increase wire size over the stock 18 ga when doing a coil relay mod. Go 16 gs if it makes you feel better but the coils only draw 3 amps. Generally the wire size is not the issue.

[posplayr]

You need a chemical cleaner like Deoxit

[JTGS850GL]

Voltage remains steady at 12.2 all the way through system even with coils connected until after the transition from o to o/w in the kill switch.

You may have found the source of your problem. Sounds like your kill switch is dirty. Pretty common problem. Measure the voltage across the switch and I'll bet you find your missing voltage.

[rgtrough]

Hey JTGS850, I wish you were right. Took the switch apart, cleaned it, still have voltage drop with the coils connected. So today I did the coil relay mod pretty easy and straight forward installation. Now I have 12.6 volts at battery and 12.6 volts at coils. Now for the bad news. In my haste to fire the engine and try to dial in the carbs I did not insulate the two leads coming from the Dyna S ignition module. You got it, screwdriver touched the bare connection and fried my module. Anybody know if there is a fix for these?

[posplayr]

Hey JTGS850, I wish you were right. Took the switch apart, cleaned it, still have voltage drop with the coils connected. So today I did the coil relay mod pretty easy and straight forward installation. Now I have 12.6 volts at battery and 12.6 volts at coils. Now for the bad news. In my haste to fire the engine and try to dial in the carbs I did not insulate the two leads coming from the Dyna S ignition module. You got it, screwdriver touched the bare connection and fried my module. Anybody know if there is a fix for these?

It is possible to get rid of the drops buy chasing down all the connections, but is many respects the Coil relay mod is the path of least resistance. Not sure how you would have damaged it except you raked it across the +12V. Make sure it is not working and then call Dynatech to see if they will exchange it.