just bought an 81 xs1100 special. need help with ignition coils....

[navy528]

hi,

just bought my first bike, an 81 yamaha xs1100 special. it ran the first day, but then #2 stopped firing, then shortly after #3 did too. now i dont if #1 and 4 are firing. i suspected the right ignition coil but how do i check the coils. i bought the clymer manual, but it doesnt go into depth of how to check the cdi box and what kind of plug caps id need if thats the problem. thanks. sean

[mro]

Pull a plug wire
stick a screw driver in it and lay it on the head where you can see it
(screw driver shaft just less than a 1/4 inch away from head)
Crank, look for spark, or lack there of

mro
BTW
have you bothered to clean all the electrical connections?
(including plug caps and maybe trim the plug wire if any corrosion present)

[Cobia]

MRO is right about checking for spark individually accross all your cylinders to determine coil performance. Another method that works for me is to remove the plugs and inspect them for color and 'wetness', if any. Wet plugs tell you that those cylinders are running rich or are just not firing at all and accumulating unspent fuel.
Then just plug each one into it's respective wire, ONE AT A TME, ground it on the head or jugs, and turn the engine over while looking for the spark the plug is supposed to create. No spark from cylinders that share a coil tells you....
This method helps you eliminate a few things at once;
If you have spark and the plug is wet.... it points to a rich condition (carbs).
If you don't have spark, and try another plug, if still no spark.....could be a bad plug, coil wires, or coil.
I would then try the 1/4" spark plug wire trim procedure, and check again for spark. If you get a spark it was the wire to plug cap connection failing.
If still no juice, clean the connections of all the wires that connect to the coils..... check again for spark.
You can be fairly certain that it's a defective coil if you still have no spark after this routine. It really doesn't take very long to do this.

Good luck

[navy528]

thanks!, this is what ive done....

thanks mro and cobia,

you are a great help and much appreciated,

i have all brand new correct spark plugs (ngk) on (gapped correctly according to the manual), the carbs are off because i found that the air filter box was full of fuel. i dont know if this is because the floats are stuck or the fuel keeps going thru as normal and its just not being sparked because the plugs arent firing. i have taken the plug caps off, cleaned them, trimmed back the wires and inch and screwed the caps back on.

mro, i did the test you said to do with each individual wire. 1 and 4 produced shock....haha trust me i know. however neither 2 or 3 did. does that mean that the right coil is bad? also, in the manual it speaks of a ballast resistor...i dont see it on the bike and the coils on there are original and do not have an internal one. how often do the coils go bad?

i have cleaned all the electrical connections on the bike with electrical cleaner and added a very lil electrical diode grease to each to prevent corrosion. none of the connections where corroded.

this site is great, and that message was my first, ill help others as you help me! when i get a hang of the bike of course.

[DGXSER]

i have all brand new correct spark plugs (ngk) on (gapped correctly according to the manual), the carbs are off because i found that the air filter box was full of fuel. i dont know if this is because the floats are stuck or the fuel keeps going thru as normal and its just not being sparked because the plugs arent firing.

Its the floats. No amount of un burnt fuel in those cylinders will turn into gas in the airbox. And the flooding carb will cause an overly rich condition in its cylinder and could be why it will not burn.

mro, i did the test you said to do with each individual wire. 1 and 4 produced shock....haha trust me i know. however neither 2 or 3 did. does that mean that the right coil is bad? also, in the manual it speaks of a ballast resistor...i dont see it on the bike and the coils on there are original and do not have an internal one. how often do the coils go bad?

Bad coils is not uncommon. You can check them by measuring resistance on both the hi and lo sides with the coils unplugged. As Cobia stated, it could also be dirty or corroded wiring. although you stated you checked and cleaned those. It also could be a bad pickup coil or more likely broken wires on the pickup coil that fires that ignition coil. Or worse case is it is in the TCI. If ti were me, I'd check the coil itself, then go to the pickup coil which is the next if not more likely suspect.

[navy528]

could it be the spark plug caps?

could it be the spark plug caps alone?

[DiverRay]

If it was the caps, it would probably be just one. They can also be measured with a VOM. If you don't have one, Harbor Frieght tools has cheap units that will work. Just watch the battery on it, the original 9v. will only go for about two hours. Replace it with a good 9v., and it will go for months.
Cap resistance should be about 5K Ohms, and between 4K and 6K Ohms should work, as long as the pair (1&4, or 2&3) are close to the same resistance.
I DO think the carbs are the FIRST thing to look at, though.
Welcome to the site.

[TopCatGr58]

Hey Navy,

Welcome. The 81 doesn't use the ballast resistor, and the ohm readings are different when testing them vs. the 78-80 series, your manual will have a supplement in the back for the later model/years.

The 81 doesn't flex the PU coil wires as much as the earlier years because it doesn't have a cent. adv. mech. The pu plate only moves with the vac. adv. pot action. The cent. adv. timing curves are programmed into the TCI...not a CDI! Also, the TCI connections can have problems...solder joints on the TCI can go bad, and resweating them can restore it.

Other diagnostics for the ignition coils is to swap their primary connection plugs with each other, and then retest for spark. The TCI will now be firing opposite pairs. IF the same 2-3 wires don't spark, then you've pinpointed it to a bad ignition coil. IF the 2-3 sparks, and the 1-4 doesn't, then the coil is good, and further testing of PU coils, and TCI are required!

T.C.

[navy528]

thanks!

thanks DGXSER, DiverRay, and TopCat,

man, this site is great, im so glad i found this. the amount of help ive recieved here has saved me alot of trouble and money. also, thanks for welcoming me here. ive ordered new dyna dual output ignition coils today (the old ones were recieving power but the right one was not working), plug wires, and caps.

thanks for letting me know that the '81 doesnt have a ballast resistor, that was worrying me alot. i began to think that the previous owner parted that out on the bike.

i cant wait until im knowledgable enough to give advice on the xs11's.

[TopCatGr58]

Hey Navy,

Not knocking the Dyna coils, but if you had looked around here or asked, you could have possibly found a cheaper alternative to the Dyna's!?

MikesXS sells a few aftermarket high and higher output coils that will work on our bikes, the black ones...rated at ~35KV, and the green ones, rated at up to 45Kv provided the coils are seeing 14+ volts!

As to the Dyna's, did you get the 3 ohm style, or the 1.5 ohm? You would have wanted the 3 ohm ones since no ballast resistor on the 81.
T.C.

[lsskitch]

I just picked up on this conversation.

I just bought a 79 xs1100. I've been through much of the same issues. I've recently noticed however, that the missing spark in one cylinder is transitory. In other words one day it'll be cylinder 1, next day 4, then 3, then 2. I've observed it (by feeling heat on the exhaust) in each of the cylinders, but only one at a time.

I'm thinking there is something where it can't spark 2 at a time, lack of voltage or ?

Have you checked to see if your lack of spark on one cylinder moves from cylinder to cylinder?
LSS

[petejw]

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[motoman]

Gas in the airbox..........pretty much a giveaway to wet fouling the plugs...........bet it didn't take long to start dropping cylinders either..........also bettin secondary ignition is workin fine........keep it simple, pull and clean up insides of those carbs, install and re-set and sync.........ride it.........pretty simple, yes?