Coils

[Edisto]

I have my fuel system all set for my 79' F. Carbs are clean, tank is clean, filters are in place. She takes a while to warm up, and when she does, everything seems ok. While test riding, she bogs down around 2-3k rpms, occasionally she will hiccup (backfire) and then she takes off. If I am reading the other threads right, this is a symptom of a coil or fire issue. In fact after riding, header 2 and 3 are significantly cooler than 1 and 4.

I pulled the coils and I am trying to test them according to the thread in the maintenance forum. I am a novice with a multimeter, but after pulling the caps off of the plugs, I tested the resistance by setting the multimeter to 20k--I got an acceptable reading of 5.2. I don't follow which other wires I am supposed to test.

Check that the primary wiring (the small wires attached to the coils) attachment points are all clean and free of corrosion. While you are at this point you can also check the resistance of the primary and secondary sides of the coils with a volt/ohm meter.

.... Measure the resistance across the wires coming from the primary side of the coil. It should read 1.5 ohms ± 10% (Note the 81 XS and the XJ use a 2.5 ohm primary coil). The Yamaha manual says these measurements are made at 68 degrees Fahrenheit (20 degrees Celsius). With those connections still apart you can test the resistance of the secondary side of the coil. Measure the resistance across the two spark plug connectors. This measurement should be 15k ohms ± 10% at 68 degrees F. (20 deg. C.). If either of these readings is infinite resistance or past the ± 10% mark, you probably need to replace the coils.

I am pretty dense. I can't get a reading no matter where I stick the leads. Can someone put this in idiot language? Thanks for the help.

[Rasputin]

Do you have access to a manual? On page 169 of the clymers it has a good picture and write up of the test. Pages 6-11 and 6-12 of the Yamaha service manula also has a good write up. If you do not have a manual you can download it from Catatonicbug's signature line.
The primary coil check is testing the two small wires that go into the coil that resistance should be at 1.5 ohms (+- 10% at room temp) unless you are running the 3 ohm coils.
The secondary coil check is from one plug wire (caps removed) to the other which should be 15Kohms (+- 20% at room temp). If you do not remove the plug boots the numbers will be different because of the resistance built into the plug caps. Hope this helps.

[DGXSER]

Also, you might start with the pick up coil wires. This is a very common failure point and could be the source of your problems.

[Edisto]

I do have the manual--I will check it out. I will check the pick ups as well.
When I pulled the caps off of the wires, one of them looked a little fried.

[DGXSER]

Well, that could also be the problem. The "wasted spark" system employed on these bikes uses both wires from the coil to complete the circuit. So if one wire is bad, it will most likely miss on both plugs from that coil.

[petejw]

could be ur float levels,
what did u set them at?
25.7mm are the stock settings for the earlier carbs.

also check u havent broken a mixture screw tip,
these are easily broken on the earlier model carbs.

[planedick]

Testing

I think what you are missing is the place to hook the other test lead. On lead from the multitester goes to the wire and the other goes to the ground (laminate stacks or mounting holes).

[natemoen]

I think what you are missing is the place to hook the other test lead. On lead from the multitester goes to the wire and the other goes to the ground (laminate stacks or mounting holes).

No, there are 2 small wire back there. IIRC there is a red/white going to both coils and then a gray on one and an Orange on the other.

[Edisto]

Good news--When I trimmed back the plug wires and tested their resistance, they measured 15.65 k ohms, and the primary wires (when cleaned) measured about 1.5 ohms. I am going to get new caps just in case and reinstall, then check out the pick up coil.

Thanks for the advice and help.

[natemoen]

Good to hear!

[cywelchjr]

That sounds good. In theory, if one knew how, you could rehab old caps by cleaning and replacing the carbon resistor with a new one, but at the price of the caps, and the time needed to clean them, disassemble and reassemble them etc, it doesn't seem worth it, and I'm an electronics tech by training (and by trade until I switched to computers in the 90's), plus the new caps just look nicer than the old grubby ones anyways.

[Edisto]

I am having a heck of a time finding boots. None of the box stores have them unless I buy a whole wire kit. I guess I will be checking online.


On another note. I cleaned my boots the best I could, rechecked resistance, reinstalled coils, and then tested. No fire on cylinders 2&3. I borrowed a spark board to verify--no spark coming from cylinders 2&3. She will crank, but 2&3 are not firing.

Back to the "search option".

[natemoen]

WWW.mikesxs.net has caps

[DAVINCI]

Nate,

Mike's also has those stainless cyl head nuts, their part#49-0247

[Edisto]

Excellent--Just ordered some for both XSs. Thanks!