Coil/TCI Ohm Gremlin like no other .....

[Barbarosa]

Haven’t read anything that’s similar to this problem so putting it out there to see if anyone has run across something like this in their troubleshooting. I recently picked up a 1980 SG that sat for an extended period of time and was said to run when parked. PO had a good story for the scooter and 2nd gear repair had been done. Got it home and did compression test readings and found 105 to 108 across the cylinders. Low, but acceptable to me as my 1980 Standard was 110 and ran very strong. Can’t remember for sure, but a couple of the plugs were sooty when pulled. No indication of catastrophic problems though. Pulled the bowls and found NO varnish or residue. Fresh fuel, new battery, clean plugs and it fired up. Bike ran with normal power off and on, pulled well through the gears and it seemed to be healthy enough to continue on. A local tech friend cleaned the carbs and the only thing odd he found was a mismatched needle and seat on #3. Put in new bowl kits, set the floats at 23mm, and synced them in. Still have misfires, mainly on #3 and #4. The plugs are not gas soaked, but have carbon on them. It will start easily and idle like before the carb work, and runs about as it did earlier. Now it also has a problem returning to idle after blipping the throttle as well. No vacuum loss or boot leaks. I trust the work and skill of this 20+ year tech so hear out the ignition test results before directing me back to the carbs.
Power at the TCI is 11v and the pickup coils read out 722 and 728 ohms with the tug and jiggle step. Wiring splice was very well done; in fact the whole wiring system looks like it has been well attended to other than the fuse box upgrade which I will do before I button it up. When I checked the ignition primary it read 9.8 and 10.3 ohms at the TCI. Way out of spec so I thought I found a problem and pulled the coils for a closer inspection. With the coils isolated the primaries read 1.6 ohms each and the secondaries were 15.2k and 15.4k minus the caps. Caps tested at 5k. I plugged the coils back in and got 14 ohms at the TCI for the primary this time. Long story short, multiple checks for primary resistance at the TCI with coils hooked up ranges from 9-15 ohms and the coils bench test at 1.6 ohms. The schematic shows the primary wires from coils to TCI as a straight shot and both wires show no resistance when tested. How can the coils read 1.6 ohms unhooked and then 10+ ohms when put back in a single wire circuit?
I haven’t ran the bike very long at one time, but it did “catch hold” on occasion and indicated it really wanted to go. The sooty plugs not being soaked and the coil reading at the TCI are what I think make this an ignition issue. Any advice from the gurus?

[BA80]

Sounds like you are having an intermittent pick up coil issue.

[Barbarosa]

Hoping it's not the pick ups since I don't have known good spares. Checking out the on-off switch next to see if that's where the extra ohms are coming from. These old eyes just picked up the switch being in circuit and it makes sense that the voltage would be effected by the resistance created by poor contact there. Start/run circuits? Will be a while before I can get back to it though. BTW this motorcycle is supposed to be from Kansas City and one of the top XS11 guys there has wrenched on it. Would any KC people recognize a black and purple flame with yin yang symbols paint job? It's signed by Spakes.

[motoman]

From what you have initially stated, the voltage is to low. should be the same as checked at battery itself, 12.5v-13.1v. That IS the first issue causing low voltages TO coils.
Second issue is no matter who your using as a supposed 'mechanic' or however long they claim to have been one, the hang idle at start-up IS from carbs not being synced and idle mixtures not set correctly nor evenly across all four carbs.
Low votage issue and a GOOD place to start is to remove and carefully take apart kill switch. This IS the notorious place for a voltage drop. Careful the teeny internal spring in it doesn't jump somewhere into no-mans land when taking switch apart. The kill switch completes the electrical circuit whether it is used or not.
Also, for secondary electrical issues(coils, plugs, etc.), remove the right side cover, unbolt the fuse panel from frame. Now unplug all five plug-ins, clean both connection pieces using a high quality electrical spray cleaner, or better yet a small bottle of De-Oxit that has the small brush attached to screw-on lid cap. The larger flat five-wire plug-in being important, as current thru that feeds the pick-up coils. Doing those things mentioned will eliminate possible issues bike is now having.
For added precaution, remove left side round ignition cover and using both hands try tugging in order to stretch ALL of the wires in that location. Any one that stretches has broken wires internally ans HAS to be cut and re-attached using a really short piece of butt conector and real short piece of shrink tubing over the fix.......BTW, another common area of a problem from the wires constant movment of the vacuum advance.

[Barbarosa]

On-off switch is next up on the menu. Thanks for the flying small part heads up! As far as the carb work goes if I didn't watch the carbs being synched and see the header pipe temps match up as it ran I would totally agree with your assessment. Only revved up one time and sort of freaked me out is why I mentioned it. Sat and idled great, but started misfiring and crapping out when driven a few miles. I'm a one carb guy when it comes to knowing much about how they work, but I did gain some experience with duals a while back with a an old Honda 450. Makes a HUGE difference when dialed in right. Medical problems prevent me from working around gas fumes (and such) now and is the reason I didn't take these on myself. No biggie if they do have to come off again for whatever reason, but I am sure hoping when the ignition is brought up to snuff the rest will respond accordingly. Thanks for the input and I will post results when I get back at it.

[motoman]

On-off switch is next up on the menu. Thanks for the flying small part heads up! As far as the carb work goes if I didn't watch the carbs being synched and see the header pipe temps match up as it ran I would totally agree with your assessment. Only revved up one time and sort of freaked me out is why I mentioned it. Sat and idled great, but started misfiring and crapping out when driven a few miles. I'm a one carb guy when it comes to knowing much about how they work, but I did gain some experience with duals a while back with a an old Honda 450. Makes a HUGE difference when dialed in right. Medical problems prevent me from working around gas fumes (and such) now and is the reason I didn't take these on myself. No biggie if they do have to come off again for whatever reason, but I am sure hoping when the ignition is brought up to snuff the rest will respond accordingly. Thanks for the input and I will post results when I get back at it.

Like I stated previously, the pick-up coi wires under the round, left ignition sideove(metal on motor portion)r being broken internally is likely the problem. Also associated with that, removing the right plastic sidecover and removing back as far as wires will allow the bolted in place fuse panel. Then unplug ALL five plugins and spray electrical contacts on both sides of plugins.
The revving one time allowed the mechanical and vacuum advance to rotate, loosing internal contact of wires under insulation. Then, riding it, being somewhat under load became the real tell-tale sign of voltage losing contact with rotation of vacuum advance assembly.

[TopCatGr58]

Hey there,

As stated, the voltage to the TCI is a concern. The 80 uses the ballast resistor system. During starting the coils get the max battery voltage for easier starting due to stronger spark, but once the bike starts, the power is then rerouted by the TCI to go thru the ballast resistor a(1.5 ohms) and then to the coils, and this drops the volts to around 9 volts. But if you have less volts to begin with, then the B.R. can drop the voltage even lower, and that can cause WEAK spark and a low rpm idle miss due to weak spark energy. Once the bike is revved up to around 2500 rpm or more, then the ALT is providing full charging power and so more of a chance to get more voltage to the coils.

Clean harness connectors can really help alleviate a lot of the gremlins.

T.C.

[Barbarosa]

Schematic makes more sense now that I know the TCI switches the circuit. Will keep plugging away till I get good voltage everywhere it's supposed to be.

[Barbarosa]

After some cleaning and TLC there is now 11.8 at the TCI. Losing a volt at the main switch and will get to that asap. Bike started easily, idled and came off idle well, and made 4 black plugs. I'm thinking progress since now all 4 are doing the same thing. Anyway, carbs are off now and I get a ultra sonic cleaner for my birthday. Just what I needed for my OCD.

[motoman]

After some cleaning and TLC there is now 11.8 at the TCI. Losing a volt at the main switch and will get to that asap. Bike started easily, idled and came off idle well, and made 4 black plugs. I'm thinking progress since now all 4 are doing the same thing. Anyway, carbs are off now and I get a ultra sonic cleaner for my birthday. Just what I needed for my OCD.

Coil ohms across coil poles should be 1.7ohms. 1.6 is on the low side and coils IMO have internal fractures in the hardened epoxy fill. after that many decades of heating/cooling cycles, tends to be a common problem with the original coils.
Low voltage at the ignition(less than the voltage reading across battery terminals) causes coils to deteriate their rated ohm(1.7) reading, and just gradually get worse. Savings of money from buying new after market coils can be had purchasing used Honda VFR coils of 1.7ohms(check with multi-meter before purchase). They are also matching bolt hole bolt on replacement, also using separate 7mm high temp plug wires of your choice!
Low voltage has two major cause areas,,,,,,,dirty ignition switch contacts and dirty, not clean contact sliders(copper) inside RUN/STOP switch. The later completes 12v circuit ALL the time, and IS a common voltage loss location.