Need spark on a 1981 Yamaha XJ750RH Seca w/ 'custom' wiring

I just bought a 1981 Yamaha XJ750RH Seca. It is very well used and does not run. According to the PO the engine is fine. Only problem is, the wiring harness is trash.

This has prompted me to attemt to wire the bike myself. I'm having 1 little issue though - No sparks.

From my limited understanding, the pickup coils signal to the TCI when to power each ignition coil. I have 3 wires coming from the pickups to the TCI. The TCI has a ground wire, a shared positive wire to both ignition coils, and a seperate ground lead to each.

I found a wiring diagram for a bike similar to mine, and all was well, except that there were four wires from the pickups to the TCI. Mine may only have 3, or it could be missing one.

Another possibility I see is that there is a switch that is supposed to be attached to the TCI that I am missing.

Thanks for the help everyone, it is much appreciated and I will post pics when she is presentable!

 

See here and here for wiring diagrams. It does show just three wires going to the pickups.

 

Re: Need spark on a 1981 Yamaha XJ750RH Seca w/ 'custom' wir

Thanks for those. Is the 550 wired exactly the same as the 750?

I believe my wiring matches that diagram, but I will double check it all just in case.

 

Ya, sorry about that. I sent you the wrong diagrams. To answer your question, yes.

Here and here are your diagrams, but you'll need the component key.

 

Mind if I ask about what a few of the components do?
I'm unsure about

5. Starter circuit cut-off relay
6. Diode Block
25. Dip Switch
33. Canceling Unit
37. Diode
47. Check Switch
48. Warning Control Switch
50. Computerized Monitor

 

the starter cut-off relay is part of the interlock system that only lets the bike start and run in certain "right" conditions. (in neutral, stand down) (in gear with the clutch disengaged, stand down) (Stand up, N) (stand up, in gear, clutch disengaged) etc, etc and prevents your bike from riding away of it's own free will.

the dip switch you're likely looking at is the one for turning on the "fog lamp/aux light". If your '81 came with a yellow lens on the fog lamp note there was a recall on those as they're illegal in most US states. I don't think we can still take it back to the dealer. I think I'm gonna turn a relay for my heated grips on and off with the dip switch when I get around installing some.

The cancelling unit is part of a mechanism that turns the blinkers off after a given distance of front wheel travel. There is a little magnetic leaf switch (forget the proper name) up in the speedo that counts the number of times the speedo cable has turned and sends pulses to the canceler which then uh, cancels power to the turn signal relay.

The way it's supposed to work is that it keeps you from being that old man in the right lane with his left turn signal on for ten miles by automatically shutting them off after travelling X fraction of a mile. The way it actually works is that it the 30 year old electrics go out and you're stuck having to cancel the blinker manually like most mere mortals. Also it generally doesn't work with replacement blinker relays which are needed with age or with the addition of LED blinkers.

The warning control switch is that button on the Atari dashboard that cancels the blinky red light of eternal annoyance. It is very important to push this button when the light comes on so that when you go around a corner and the gas sloshes in your tank the red warning light can come back on alerting you that you're low on gas (about a third of a tank left)
That way you can divert attention back to the light and taking your hands off the bars to push the button again. Riding like that for several miles is part of the airforce training program to be a fighter pilot.

The Check switch is the button next to it (my friend says it's her favorite feature) that while the bike is running makes the LCD panel go through it's check list of possible problems. Refreshing your info regarding important stuff such as whether your battery fluid is low or whether or not your kickstand is down.

If I remember right some of the diodes are for the blinkers too. I'm sure I would know more if mine have ever gone out.

I talk a lot of trash about my bike. It's out of love. We're like family or at least very good friends.

 

Thanks for the info!

Unfortunately, it looks like my wiring is good... Guess that means something is broken. Anyone know how to test the pickup coil, TCI, and ignition coils? I have a DVOM and pretty decent set of tools available.

 

testing coils. Haynes says:
primary resistance = 2.5 ohm +/- 10%
secondary resistance= 11k ohm +/- 20%
US models evidently have plug cap resistors of 5k ohm on 1&4 (outside cylinders) and 10k ohm on 2&3 (inner pair of cylinders)

pickup coil resistance = 650 ohm +/- 10%

If I were a betting man I'd gamble that it was the TCI if for no other reason than it is the mysterious black box inside which VERY few wrenches dare venture.
I'd test the IGN coils and if they're good I'd toss a coin between bothering to test the pick-ups and just sourcing and ordering a TCI.

Note, my advice in this matter is quite unscientific, your results may vary.
This is based solely on my own anecdotal experience with my own and friend's bikes over the last few years. Never seen pick-ups go bad, even when others INSIST they're to blame.

The stats from the Haynes book are accurate though

 

Correct me if I'm wrong, but I believe you'll want to first unscrew and remove the plug caps from the coil wires when you test the secondary coils.

 

yes. there are resistors in the plug caps so in order to test the coils do just exactly that. Test the coils separate from the wires with caps.

 

I'm having similair issue with my 81 seca, except mine the start button wont crank over the engine I have to apply power to the starter solenoid to get it to Crank over. Still no spark either way?

 

Bo your problem is you removed the atari package answers on where to start are posted in your thread you started.
http://www.xjbikes.com/forums/threads/1981-xj750-seca-no-start-no-spark.116712/#post-583772