1982 XJ750 Seca - Ongoing

if your coils are acting up from heat, it's going to be in traffic, stop n go, heat comming up off the engine type stuff. out on the road they would stay cool from the breeze. if it it coils your going to lose two cylinders at once
what's up with #1 plug?

 

That first pic is of the oil drain plug.

 

It was carbon... wiped right off

Colortune will take care of it when I'm done

 

Was this done with the spark plug caps still attached? If so, you could have a problem with the caps or the connection with the caps to the plug wire. Will see what you get with the other meter but I suspect it will be the same. If so, remove the caps and check individually and check the coils with the caps off. You may just need to trim a 1/4 inch or so from the plug wires and reattach the caps if the parts ohm out OK individually.

Those plugs do look a bit old and tired. It also looks like you are running the BPR version (resistive). That probably wouldn't matter much but Yamaha calls for BP7ES (non-resistive) for the 750 Seca.

 

A coil changes low voltage to high voltage, like a transformer and they do produce heat.
They can get worse with heat and run time, the wires inside separate, I'd replace the one coil that is out of spec.
Consider doing both as the have the same hours on them, also, unless they are new change the caps with the new coil(s)
The resistors in them can break down and cause coil damage if they overdraw (resistor shorted) too much juice thru coil, or under draw (resistor too high) not enough juice, it builds up in coil.
Side note you can test the caps 5K ohm resistance +\- 10%
Hope this answers your question.

 

As per resistor plugs, they suppress RF interference, they may foul easier, but won't hurt if it calls for non-resistor.
Never! Run non-resistor if it calls for resistive, it can damage coils or worse CDI...

 

It was with the caps attached as they are the original and not removable and the hayes says should be 11K ohm with caps, so if that's wrong I would expect 21K, or 11+ caps...

I remember asking for regular plugs, must not have noticed the guy at the store gave me the "R".

 

You can't even buy non-resistor plugs here anymore, unless you can find some old stock. I have to order them online.

 

Well, Haynes got that from the Yamaha FSM, so both are incorrect. You should get as you suggested, 11K plus plug caps.

The caps are removable (turn CCW and pull lightly) and should be 5K each on the Seca. Once again the FSM gets this wrong saying the 2,3 caps are 10K, Len gets it right as usual. For whatever reason it seems the 1, 4 caps are most prone to failing by going above spec. The longer 2, 3 caps can actually be dis-assembled and cleaned.

https://www.xjbikes.com/forums/threads/the-ultimate-relay-switch-sensor-and-diodes-guide.27543/

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

 

Caps are removable from end of wire?? I had tried... didn't seem to be.

 

Yes, and some aftermarket and OEM coils
are interchangeable, and have removable wires too
(GPz900R Kawasaki springs to mind, only 'cos I had one of those, eons ago, and succesfully used a set of those coils/wires on my XJ's.......)

 

They screw into the copper strands.

 

Well, I went to the shop and got non-resistive plugs... will save the others as emergency back-ups.

 

Thanks a bunch gang... believe I found it.

Now I see how the plug caps are attached (Not a fan I must say). Removed caps from suspect coil and clipped back leads to where I got solid copper with tight insulation. Ohmed out at a perfect 11K. Put caps back on... nothing. Found one cap had no resistor that I can find. Really looked and don't think I dropped it? Anyone think I could have been riding around missing a resistor completely? The spring was broken in half and the bottom of the brass plug was black instead of shiny like the other so I think so...

Anywho… took another cap off my parts bike that guts looked really good and now perfect 21K through caps and coil. Will do the other one tomorrow as it's reading 30K. Looking forward to Colortune and sync since I have it apart anyway and weather is supposed to be awesome later this week.

 

So the bike seemed great for a couple days... then the same thing started up again. On doing the other coil / caps mentioned above, I never got the assembly down to the 22K ohms required. It was 28K.

I'm going to pool all the parts with the other bike I have and see if I can get the real 22K I'm looking for through each coil.
Then if she acts up again start looking at the TCI. Or at least take the time to measure when it's hot and actively exhibiting the problem. Maybe I will only get wonky readings then.

The correct plugs are brand new and gapped so shouldn't be that... Oh, and found that resistor I thought was missing and it was open resistance and 1/2 brown / burnt, so thought that was most of the original problem but I guess not.

 

Done dealing with these old plug caps and resistors...

Suggestions on inline splice plug cables?

 

If I had to do it I would either go with new Dyna Coils or the Honda coils that are a good match. Splicing just seems half a##.

https://www.xjbikes.com/forums/threads/dana-coils-a-must-upgrade.118318/#post-592895

https://www.xjbikes.com/forums/threads/yes-dynatek-coils-make-a-difference.117797/#post-589572

 

Agreed, it "seems" so, but my $1,300 bike is now a $2,000 bike, and when it becomes a $3,000 bike I'll be pissed enough to just buy a $7,000 bike and not have to fix it every two months.
I spent $32 connectors, $30 caps, and $15 wire. With coils the connectors turn into at least another $80 for those coils. I have four original coils off two bikes I have, each of which ring out to in spec at 2.5 ohm and 11K ohm so I have to believe two of them are good.

And if I do end up getting coils eventually, I still need the wire and caps and the connectors go in the toolbox for the next bike . The caps are what is falling apart on my bike... that last post was after mixing and matching for an hour and not being able to get stable cap and resistor readings.

 

FWIW, new caps from Yamaha aren't bad. I think I did my bike for $25-ish. They are really simple to replace. Unscrew the old ones from the wires, snip 1/4" off the wire to get fresh copper and screw the new ones on. Job done!

Edit: I say from "Yamaha", but from a dealer's parts counter, I got the NKG caps. 2-90 degree, 2-60 degree.