Cylinders 1&3 not firing

[Blackdog]

Ran spark test and all cylinders spark, but it is a weak spark. Rebuilt carbs, spark plug caps, checked connectors. Kind of hard imagine 1&3 not firing, but thats what I've got. Am going out right now and check voltage to coils. My guess, just an overall weak system due to what i don't know.

[trbig]

Fuel is cyls 1&2 and 3&4 together. Electrical is 1&3 and 2&4 together. (Usually) Suspect a coil, but also check your pickup coil and p/u coil wires.

Tod

[Blackdog]

resistor

found bad resistor in plug cap, need to replace it but I really don't think that this the ultimate problem, cyls 1 and 3. I doubt I can find a replacement resistor and a couple of days ago I asked at Advance auto and they said they had no caps that weren't fused to the wire. Guess I will have to go online. Don't know why they only had resistor caps on cyls 2&3, but I guess they have their reasons.

[DGXSER]

Had a similar issue, mine was fuel related. If you recently worked on the carbs I am betting on fuel issue.

[Blackdog]

carbs

Bike has been sitting for many years, it was running fine when I stopped riding. Had to clean carbs because they were frozen shut. So it not a case of it ran fine, I cleaned the carbs, and now it doesn't run. Fortunately the bike has been garage kept all it's life, all connectors I checked, spotless. Opened up the tci box and it looks like new. Battery at 11.9 volts, voltage going into coils 10.9.

[Blackdog]

more

resistance of plug wires is 11.9 and 12.09 with no caps.

[TopCatGr58]

Hey Doug,

Okay, had to check your Profile to see that you have an 80 MNS, would be easier to have it listed in your SIGNATURE that shows with every post/reply you make!

Your battery is a tad low, should register a bit over 12 when fully charged. The voltages to the coils, where these measured when it was running, or before you started it? The XS's TCI routes the power directly to the coils for full 12 volt starting power, but once running, it then routes it thru the Ballast Resistor to protect the coils, and so ~9 volts is normal thru the BR.

As Tod rightly stated, 1-2 and 3-4 are usually carbs, and 1-4 and 2-3 are usually ignition components, coils, PU coils, TCI, etc. A member posted problems with the odd pairing of cylinders due to low voltages to ignition coils, enough to fire the primary plug but not the secondary one on each coil.

Those resistance measurements are not within spec! Should be 15k +/- 10%. MikesXS sells a few styles of plug caps, resistor and non-resistor. Do you have a NAPA or Bap/Geon import parts store, might find some caps there?

Even though garage kept, can still develop corrosion, would suggest cleaning all contacts in ignition system.
T.C.

[Blackdog]

coils

Actually its an 81, the voltage to the coils was measured at the pull apart connectors right before the coils, they were disconnected when measured, engine off, key on. It has plenty of power to turn it over nicely. I can't imagine how both coils could go bad by just sitting there. Like I said #3 spark plug cap was toast, resistor burnt out, if that will help. At this point I am just going over the whole system looking for something wrong. If 1-2 and 3-4 are usually carbs, and 1-4 and 2-3 are usually ignition, what does 1-3 mean? Thanks for your help.

[XJOK2PLAY]

[Quote = "If 1-2 and 3-4 are usually carbs, and 1-4 and 2-3 are usually ignition, what does 1-3 mean?"


AS previously posted by Trbig:

Fuel is cyls 1&2 and 3&4 together. Electrical is 1&3 and 2&4 together. (Usually) Suspect a coil, but also check your pickup coil and p/u coil wires.

Tod

Perhaps you maybe confused, which can complicate an already complicated procedure...
Hope the second time around is clearer...


1 coil fires 1 & 3, the other fires 2 & 4... ignition system is a "wasted spark" type system, meaning the coil fires every time, even when the other cylinder isn't ready to fire.

[Ivan]

Actually I think Tod mistyped that. The outside pistons are paired and the inside pistons are paired on the crank, thus the spark has to be as well, so its 1&4 and 2&3 on the ignition.

[Blackdog]

Confused

I just went to recheck to be sure, but on my bike the left coil has long wires with the factory labels on the plug wires that say 1&4. The right coil has short wires and says 2&3. I understand about the wasted spark, and I am going to assume that the 1&2 and 3&4 on the fuel is due to the left and right banks of carbs are fed from two different sources. I surely must be missing something here, why would Yamaha put both resistor caps on one coil. I am just telling you what I am seeing on this bike. I'm not trying to be snarkey here, I really appreciate the help I am getting. As I say I'm just confused. Also this is an 81, would that matter?

[Blackdog]

Sorry

Sorry I had started typing my reply to XJOK2PLAY when I went out to check wiring, came back and finished reply and posted. Ivan must have posted during that time. OK lets get back to basics, should I be getting 12 volts to coil with engine not running?

[DiverRay]

The coils should have 12V. if you DO NOT have a ballast resistor. Look just above the left exhaust cam, and see if you have a 2" long silver box with two red/white wires connected to it. If you do, you have a ballest resistor and will only have about 9V. when running. If you do not have the box, you should have 12V. when running. The COILS TYPE will determine the need for the resistor.
New NGK caps can be ordered through ANY auto parts store that carries NGK spark plugs. Most of the kids don't know how to use a parts book, and just say they can't get them! As you have ONE known bad cap, I would just replace all 4. Be sure to cut about 1/4" off the end of the wire before screwing on the new cap. And if you can't get the "long" caps, don't worry. I use all short caps on my bike with no problems. I also use a 1K Ohm cap, not 5K Ohm like factory. This allows me to use the resistor plugs with no problems, and gives me a choice of what plugs I use. I just put a set of BPR6EIX NGK plugs in daily ride yesterday, after installing mikesxs green coils.

[Blackdog]

resistor

I have no ballast resistor.

[Blackdog]

caps

Just ordered new caps, will arrive in 2 days. Anything I can do in the meantime besides check more connections?