No spark on Ignition coil 2/3 no idea what it could be

Hey guys,

So my Dad and I have recently restored his old Yamaha Seca XJ750 and put in a new motor on the old frame. The problem is there's no spark on the Ignition coil 2/3, we've replaced one and tested this one with a multimeter discovering it works fine as it had a resistance of about 2.8ohms on the primary and 30 0hms on the secondary wires. We've replaced the TCI as well as checked the pickup coil which had about 700 ohms meaning it works fine aswell. Battery is fully charged, we checked and made sure there's a solid ground to the bike frame. We have continuity between the battery and the plug which connects to the ignition coil.

Also something weird is that the turn signals stay on at all times. We took the grey cord out of the plug which connects to the ignition coil and they turn off. We've checked the wiring diagram and there's no solid way that we see how the TCI and the turn signals are even connected. Seemingly only by the battery itself.

Important to note cylinders 1/4 work fine however when we try to pull the throttle it stalls out.

We dismantled the carbs and soaked each one in a chem bath for about 7 hours each. Reassembled them and they work fine. We even used a different set of carbs to ensure that it wasn't them.

The bike can start and idle with turn signals on and cylinders 1/4 running, but we don't even get a spark on the coils 2/3. If you can help us figure this out it would be GREATLY appreciated because we have run out of options. We've also checked the wiring on the bike and can't find any significant pinches or damage to any wires.

 

disconnect the flasher relay for now
on tci disconnect the black/white wire. at bullet connector.​

have you tried new sparkplugs for 2 and 3 or swap 1 and 4 plugs into 2 and 3
next step would be swap ignition coils.

30 ohms on secondary?? is this a typo? out of spec.

coils with caps on them should read 21K ohms

ohm out the spark plug caps seperatly from coils trim wire back about 1/8 to 1/4 inch incase they are corroded.

when you measure the pickup coils also measure the 3 wires to ground that would be the orange gray and black wires from tci plug and disconnect the plug.
can you photo the tci connectors to see it plug is in upside down?

ignition specs
XJ750 air-cooled models:

Pick-up coils:
650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range


Ignition Coils:

Primary side (input from main wiring harness):
2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

Secondary side (spark plug wires, without their end caps):
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range


Spark plug caps:
1981-83 models: 5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range
1984 RL models: 10K +/- 20% = 8,000 to 12,000 ohms per cap acceptable range

Spark plugs:
0 ohms per plug

 

turn signal on all the time ? on and flashing or solid on
both sides or just 1 side
also when bike starts measure running battery voltage

 

Kind of a WAG, but have you done any work in the headlight bucket? It is possible to inadvertently reverse the tach and turn signal indicator connectors as the two connectors are identical. Is the tach working? If so, then likely not the problem. Note 3 pin tach connector BR / Gy / Blk, turn signal indicator Br / B / Sb.

 

I can't even explain my gratitude. That was the problem!! It was so simple and yet it had us running in circles, after we switched them the turn signals came off tach started working and all four pistons were pumping. Hearing that baby rev was music to my ears. I'll send pictures in here of the rebuild for anyone curious and I hope this helps anyone in the future with the same problem.

Thanks to everyone on this forum!

 

keeping any bike related issues in this thread will help.

 

Strange things are happening with this bike. It ran fine yesterday, yet today only pistons 1/3 are pumping. We've replaced the spark plugs and checked and all spark plugs are getting a spark, yet pistons 2/4 aren't pumping. We didn't change anything except put the dash back together yesterday.

The headlight also stopped working, we inspected all the wires inside the front and they all seem to be snug and in the right places.

It's strange how there's a spark at the spark plugs, but the pistons aren't moving. We completely cleaned the carbs and soaked each one in a chem bath. Made sure it wasn't the ignition coils either as we checked them with the multimeter and they have the right ohms. Also pistons 2/4 aren't working which have different ignition coils going to them. STRANGE.

Does anyone know what else might be missing if there's a spark and adequate fuel why the pistons won't move?

 

How have you determined that the pistons aren't moving?

Pistons are a physical connection that don't rely on anything electric, if you have a pistons that's not moving you have a VERY serious issue.

I suspect the headlight issue is important as a lot of connections happen inside the headlight bucket

 

I'm using the wrong terminology, my dad told me the correct way to say it is that it's skipping or missing on cylinders 2/4.

 

OK. That could still be spark. One important thing to check is that the correct coils are hooked up to the correct cylinder pairs.
The left coil goes to 1 and 4. The right coil goes to 2 and 3.
This may just be an issue of improper spark timing, which would ocur if the plug leads are not in the correct locations.

There is alos the possability that the plug wire insulation (or the coil case) has pinholes or cracks, which would cause an intermittent spark due to the magic pixies leaking out from the wires and onto the head instead of dancing down to the sparkplugs.

 

So I typed the following on my phone, but by the time I was done, k-moe had already responded, but dang-it that was hard typing so I'm posting anyways!

(also, left is seen as if you were sitting on the motorcycle)

Ok, as we are seeing the terminology is super important to diagnose things through the internet.

How have you determined that 2&4 are missing?

Have you checked your spark ( pull plug 1, rest the threads on the metal of the motor, press starter button, see spark, put plug 1 back and then onto 2, etc)

 

can you retest the secondary on the coils and spark plug caps individualy? caps unscrew from wires
you test secondary from plug wire to plug wire.

30 ohms is wrong and 30k ohms is way to high for oem coils.

 

Hello all we've figured it out.

Earlier on this rebuild we had to clean the petcock on the gas tank because it was really clogged up. This was after we soaked the carbs in the chem bath. Thinking that the dirt from the petcock might've made its way into the carbs we took the carbs apart again and cleaned them with BG throttle body cleaner put them back together and adjusted the pilot screws on top of the carbs. They were strangely turned so we put each screw to 2.5 screw turns out. Put the carbs back on and viola she worked like she did yesterday. Although the headlight still isn't on...

For those wondering how we diagnosed that it wasn't the spark plugs or ignition coils we started the bike with a plug in each coil and observed a spark in each one. Also while the bike was running we took off the top of the coil on the spark plug and noticed that when we took it off of 2/4 nothing really changed in the engine, however when we took it off 1/3 it was noticeably less loud. Checked the coils with a multi-meter and measured the right ohms on each coil's primary and secondary wires.

Once again thanks to everyone on this forum, probably am not in the clear to be done with this bike yet; but I couldn't have come this far without you all.

 

Yeah typo I meant 11k ohms don't know where 30 came from

 

Carbs was the next place that I (and probably everyone else) was going to send you, precicely because of the crap that can be inside of a fuel tank.
I mentioned spark because that's easier to check, and it's not uncommon for the plug wires to be switched around.
Fit an inline fuel filter between the carbs and the petcock to prevent needing to take the carbs off again anytime soon.

 

Another day another problem...

trying to figure out why the headlight isn't on my dad got some wires and was attempting to bypass the headlight relay to see if the headlight would come on. When doing this he put one end of the wire in the light blue wire socket and one in the black/yellow wire socket. When he did this there was a spark and the neutral light went out and now the bike won't turn over or start at all.

We used a multi-meter and all the fuses have good voltage. Ones in the fuse box and the headlight.

I read that the light blue wire is runs to the neutral light, so this may have a part to play, but I don't understand how it would short out like that or what even happened to it.

Anyone got any ideas for this one?

 

Your dad very likely killed the igniton safety relay or the diode block.


Do you have any sort of service manual or wiring diagram?
If not, get one before trying to bypass anything.
Better yet reference this thread:The Ultimate Relay, Switch, Sensor, and Diodes Guide

The best way to test a headlight to see if it works it to unplug it and hook it up directly to battery voltage.

 

We have the original service manual and I just went through it. You were correct he was messing with the starting circuit cutoff relay instead of the headlight relay. He put a wire between the Sky Blue wire and the Black/Yellow wire.

Are we going to have to replace the ignition safety relay?

 

Maybe.
Turn the ignition on and listen for an immediate click. That is the igniton safety relay energizing. It's no guarantee that the relay is still good, but it will let you know that the solenoid coil was not burned out by the short. As long as the coil is still good the relay should work.

 

Tried it and no click. Does this mean the relay is bad or the coil was burned out?

 

The coil is part of the relay.

I'd like @Rooster53 or @XJ550H to chime and double check my thinking, but if the relay isn't engaging with voltage applied (double check that you have 12 volts at the R/W wires. both should be hot when checked against the frame ground) then the realy is dead.

That does not rule out damage to the diode block. Both are part of the circuits that were jumped.

It may be that damage to the diode block is preventing the relay from having access to ground so it can engage.

 

it depends if the other safety switches and relays are in the correct place and working

you can test the diode block it is a bunch of diodes and 1 resistor.

 

confirm relay inked 4H7-00, 4H7-01, or 12R-01 on the top face

test coil of relay for ohms per manual

then do a battery test


with meter set to diode you should get reading in one direction only

 

Think this is what I need to do, checked the voltage at the R/W wire and there was nothing, on one of them and about 12V on the other R/W wire.

The R/W wire coming from the TCI has voltage, but the one leaving doesn't have voltage.

I did the test described above and everything went as it should've. This leads me to believe that the diode block is where the problem is.

Going to test it and will report back

 

If your dad truly jumpered just the B/Y and Sb wire that should not have hurt anything. The key here is that the neutral light is not illuminated, and the bike is not going to crank without being in neutral. I would investigate the neutral light first by:

Do the horns and flashers work which indicates signal power is present?
If the horns and flashers work, then either the the bike is not in neutral or there is a problem with the neutral switch, wiring, or bulb.

The bike should also crank in gear, but only if the clutch is pulled in AND the side stand is up. You will need a working clutch and side stand switch for this to happen. Note also that you don't technically have to be in gear as this method could be used to start a bike in neutral that had a defective neutral switch.

You really can't burn up the coil in the relay as it normally receives the full battery voltage across the coil, therefore there is no way it can be connected to damage the coil. Now you can damage the diode in the Starter Cutoff Relay and the Diode Block if the Starter Cutoff Relay is inadvertently installed into the location for the headlight relay or through some other creative jumpering. Unfortunately, all 3 relays have the same pin configuration so care must be taken to ensure the correct relay goes to the correct spot. Yamaha did this by providing a visual aid on 2 of the 3 relays by marking the relay with a yellow and blue dot and wrapping the main harness with a corresponding matching color.

 

Just tried this and the bike started when doing this! Already ordered a diode block so will probably put that in anyway. But now I am going to investigate the switch, wiring or bulb.

 

We've done some testing and determined that the bulb is good, the wires going to the bulb and the neutral switch have continuity, but how do we test the neutral safety switch?

Bike will start and run if clutch is pulled in and sidestand is up. Also the lights on the dash work fine, turn signals flash and warning light works.

Cancel the first sentence above, we connected a wire from the neutral switch to the frame of the bike to ground it which should've turned the neutral light on but did not. This leads us to believe the only thing left not working is a diode in between the clutch switch neutral switch. does anyone know where this diode is located?

 

neutral makes ground when in neutral, hook a meter to it and battery ground when in neutral you should get 0 ohms when in gear meter shold have no reading .
or you can use a test light hook to neutral switch and positive on battery.
if good hook to the connector that is at end of wire going to neutral switch repeat above tests

 

you would have to hook wire from harness to ground not wire from switch for your test

that diode is in the diode block

 

This is what I would suggest for checking the neutral switch:

Set the DMM to the 200 ohm scale
Remove the starter cutoff relay and place one lead of the DMM on the Sb wire
Place the other lead on battery negative or to engine ground
Place the bike in neutral, you should have a reading close to zero ohms, although often times it will be quite a bit higher and may bounce around if the shift lever is wiggled a bit.
If it reads open then take the lead from chassis ground and touch it to the terminal on the neutral switch to verify the wiring is OK - you can also jumper that terminal on the neutral switch to chassis and the neutral light should illuminate. Note accessing the switch is a pain as it is buried up under the exhaust and behind the frame.

Note also there is a bullet connector between the starter cutoff wire and the neutral switch that connects the neutral switch to the main harness. Since you did an engine swap it is possible the wire is not connected or was damaged during the engine install.

You do not need a good diode block to illuminate the neutral light

Neutral switch