vacuum advance chattering

[spectra]

i'm getting 12.9 at both the battery and the coils at idle. voltage at both ends rises and falls at the same rate through the rpm range. i trimmed my plug wires back some and took it for a ride but nothing changed. how do i test the coils resistance and what numbers am i looking for?

I have been keeping up with this thread as I have issues and tested mine today 12.75 or so at the battery and 11.09 or so at the coils............not sure if that's good or what?

As for the coils get your meter and pull the tank as the wired are under it. The same wires you checked for voltage you use for the positive the gray one and orange one are the negative. Also pull the spark plug wires why I am not sure. Anyway you should have 1.5 on the coils if 79 and I think its 3.0 or 5.0 on the newer ones? I have a 79 so.......there is a thread here on the forum for it if you look.

[motoman]

Meter set to ohms. Meter leads across coil leads of coils themselves.......should and need to be 3ohms for 81XS and XJ. My cut-off point in this case is 2.9 to 2.8ohms. Even at this point, there is internal voltage leakage and coil replacement is definitely gonna need to happen.....or a long walk, your choice.

Internals of STOP/RUN switch is another area for corrosion resulting in voltage drop.

[motoman]

I have been keeping up with this thread as I have issues and tested mine today 12.75 or so at the battery and 11.09 or so at the coils............not sure if that's good or what?

As for the coils get your meter and pull the tank as the wired are under it. The same wires you checked for voltage you use for the positive the gray one and orange one are the negative. Also pull the spark plug wires why I am not sure. Anyway you should have 1.5 on the coils if 79 and I think its 3.0 or 5.0 on the newer ones? I have a 79 so.......there is a thread here on the forum for it if you look.

3ohms for 81-XJ.

[TopCatGr58]

I have been keeping up with this thread as I have issues and tested mine today 12.75 or so at the battery and 11.09 or so at the coils............not sure if that's good or what?

As for the coils get your meter and pull the tank as the wired are under it. The same wires you checked for voltage you use for the positive the gray one and orange one are the negative. Also pull the spark plug wires why I am not sure. Anyway you should have 1.5 on the coils if 79 and I think its 3.0 or 5.0 on the newer ones? I have a 79 so.......there is a thread here on the forum for it if you look.

Hey Spectra,

The 81 of TJ as Motoman said uses the 3.0 ohms coils, but ALSO it doesn't have a ballast resistor. Your 79 if stock will have 1.5 ohm coils and the 1.5 ohm ballast resistor. Were your voltages RUNNING or just Key On?

When you first turn the key on, the TCI bypasses the Ballast Resistor(BR) and sends the FULL 12V to the coils for stronger spark energy for easier starting. Once the bike is running, the TCI routes the coil power thru the B.R. and this drops the voltage a volt or two to help the coils run cooler, not burn up!

SO...if your values were while running, that's about PAR or a little better. But if it was just KEY ON, then you ARE loosing voltage somewhere, and as has been pointed out before, the Emergency Run/Stop switch as well as the many harness connectors for the ignition system are all points for corrosion and voltage drop.

Here's what it looks like and where it is, the little silver thing just below the tank, near the front left side.



The other measurement is THRU the 2 spark plug leads for each coil. Should be done with the CAP TAKEN OFF, then you're looking for ~15Kohms +/-10%. Check the wires/caps for green copper corrosion. Also the caps have an internal resistor and so there are other corrosion points inside it, as well as the resistor itself going bad, so Ohm checking the caps is also important, should be ~5k ohms.

T.C.

[spectra]

Hey Spectra,

The 81 of TJ as Motoman said uses the 3.0 ohms coils, but ALSO it doesn't have a ballast resistor. Your 79 if stock will have 1.5 ohm coils and the 1.5 ohm ballast resistor. Were your voltages RUNNING or just Key On?

When you first turn the key on, the TCI bypasses the Ballast Resistor(BR) and sends the FULL 12V to the coils for stronger spark energy for easier starting. Once the bike is running, the TCI routes the coil power thru the B.R. and this drops the voltage a volt or two to help the coils run cooler, not burn up!

SO...if your values were while running, that's about PAR or a little better. But if it was just KEY ON, then you ARE loosing voltage somewhere, and as has been pointed out before, the Emergency Run/Stop switch as well as the many harness connectors for the ignition system are all points for corrosion and voltage drop.

Here's what it looks like and where it is, the little silver thing just below the tank, near the front left side.



The other measurement is THRU the 2 spark plug leads for each coil. Should be done with the CAP TAKEN OFF, then you're looking for ~15Kohms +/-10%. Check the wires/caps for green copper corrosion. Also the caps have an internal resistor and so there are other corrosion points inside it, as well as the resistor itself going bad, so Ohm checking the caps is also important, should be ~5k ohms.

T.C.

Thanks and values were taken with the motor off. I have also went through the start/stop switch and it is new also. Ignition was cleaned also at the connectors.

So far so good though bike is still running

[hyperballsmcgee]

just to clarify in case i am misunderstanding, primary test is one dvom lead in each small wire and secondary test is one lead in each plug wire?

[motoman]

Mine has always (13yrs) had about 6-7in. at idle. Valves and everything is adjusted correct. 175psi compression on all 4. Not saying what's right or wrong. Just saying. MHO.

Yup......and your missin' a whole lot of power. Initially needs a CORRECT mixture setting...then carbs re-synced. Vac. ins. should be in the 20-21in. range.

[hamjam]

Refer to post #2. At an idle, vacuum should be 20in. at your near nothing elevation. Here, at my location(elevation 5,000ft.), in. vac. is at 18in. Definitely a low voltage issue AT the coils, in your bikes case.

carb sync vacuum s all have a constrictor or something in the lines to lessen fluctuations so it wont be the same as using a normal vacuum gauge

[motoman]

carb sync vacuum s all have a constrictor or something in the lines to lessen fluctuations so it wont be the same as using a normal vacuum gauge

Incorrect.......only the vacuum port on carb #2 have a built-in restrictor in order to eliminate vacuum pulsations of vacuum advance diaphram.

[hamjam]

incorrect ...my set of gauges come with a restriction plus a valve to settle the fluctuations
the gauges not the bike ones made for syncing not for measuring raw levels

[motoman]

Got it..........initial statement was a bit confusing.

[hyperballsmcgee]

so putting the a meter probe into each small wire, then into each plug wire i get no resistance on either coil regardless which test was performed. kind of why i was wondering if i'm doing the test correctly or not... seems odd that both coils would fail both tests...

[DiverRay]

You need to test the two small wires together, a probe on each wire. If a '78 or '79 it should be 1.5 Ohms resistance. 1980 up should be 3 Ohms, again, this is ONLY the SMALL WIRES that plug into the harness.
The next test is the two spark plug wires. Unscrew the spark plug caps off the end of the wires and test one wire to the other. You should have about 15K Ohms as stated earlier in this thread. Then test the spark plug caps, one probe in the spark plug side and the other in the wire side. This should be about 5K Ohms. If it's above 6K Ohms, it's bad, above 5.5K, I would not be using it, though it would work.

[hyperballsmcgee]

so getting no resistance on primary wires and erratic open resistance in plug wires indicates that BOTH coils are bad? seems odd that they'd both be out

[motoman]

so getting no resistance on primary wires and erratic open resistance in plug wires indicates that BOTH coils are bad? seems odd that they'd both be out

Not particularly. If initial voltage drops below 12v, for whatever reason it tends to mess with coil output and ohms over a period of time.