4R0 ignition swap to '79

[BA80]

It doesn't need the BR, and all he has to do is make a jumper wire to plug into the harness bypassing the BR for the time being.

T.C.

Like Scott said, running the 1.5 ohm coils without the ballast resistor will fry something. Probably the TCI.

Scott says it should be OK with the BR so............

I would still rather swap out the mechanical parts over the electrical.

[Dbshea]

Like Scott said, running the 1.5 ohm coils without the ballast resistor will fry something. Probably the TCI.

Scott says it should be OK with the BR so............

I would still rather swap out the mechanical parts over the electrical.

Greg, I've got the 3 ohm coils that came from the same bike as the engine. IF I was reinstall the 4R0 ignition it would be the whole kit and kaboodle. As best I can tell the ONLY difference between the 79 tci wiring and the 81 is the lack of red/white wire that feeds the ballast resistor. So, if I was to use the 4r0, I would remove the ballast resistor completely.

We are in agreence that the 79 ignition will not play well with the 81. So one way or another I've gotta remove it from the 81 engine and install something in its place. My two options are to either reinstall the 81 equipment or open up an '80 parts bike and use that. Obviously the 4r0 is less hassle as its sitting on a shelf... Now, as to curves, if I can use the 4ro box with the 4ro engine, is there any reason not to? Aside from the road side failure (which is theoretically negated by carrying my spare yellow box) i can't see why I wouldn't run the matching set. Am I wrong in assuming that while the 80 curve is a good compromise, the 81 would be exact and the best option?


3phase: I have a 79 standard, swapping in an 81 engine. So all 79 wiring, 81 components.

[BA80]

I was just worried that running that TCI with the resistor may cause an issue with the electrickery part. I know that the 81 coils work great on the earlier bikes if that resistor is removed, that's how I have my bike, just wasn't sure about the other way around.

Yeah, just take that resistor off and plug the red/white wires that go to it together to run the 3 ohm/81 coils. As long as the wiring in the harness for the TCI is the same.

That's what I'm worried about but, 3Phase should know. That's his thang.

[3Phase]

Tanstaafl

Yeah, electronics is my 'thing'. Truth is, I hate electronics and computers but I spent gobs of money, went back to school, worked hard and had to study my ASCII off because it does not come easily or naturally to me. "There Ain't No Such Thing As A Free Lunch."

3phase: I have a 79 standard, swapping in an 81 engine. So all 79 wiring, 81 components.

You should be fine if you use the 4R0 TCI and timing assembly including the vacuum advance can. The TCI is designed for ~ 3 Ohms so it doesn't matter if you use 1.5 Ohm coils with a 1.6 Ohm ballast or just use 3 Ohm coils: 3 Ohms is 3 Ohms.


Don't worry about the Red/Yellow and White/Red wires in your '79 TCI harness connector. I did some digging and it looks like the '81 schematics in the fine manual are worng and the wires were deleted from the '81 harness and their pins are empty in the 4R0 TCI .

Here's an old picture of the '81 TCI wiring with no Red/Yellow or White/Red ballast resistor bypass wires:




Just for grins and giggles, the XJ1100 TCI may not work with the XS1100 and vice versa because the pick-up coils are different but I'm pretty sure the TCIs are electrically safe if you mess up and plug in the wrong one.

The major difference between the harness connections for the XS and XJ TCI is the XJ11's Black/Red wire for the Boost sensor is in the same position as the XS11's ballast bypass White/Red wire for the ignition coils.

[TopCatGr58]

Hey Scott,

Well, I know an 81/4RO TCI has been used on an XJ11 and it had the same amount of power as the XJ TCI according to the seat of the pants perception of the owner that couldn't find an XJ TCI, couldn't get his repaired, and tried a 4RO box, since it also has the Cent. Adv. curves programmed in it like the XJ's. And he didn't report horrible fuel mileage either despite that he didn't have any vac. adv. input. And since the ports for the boost sensor on the TCI are the same ones that are blank/missing on the 4RO TCI, you are right, it is/was electrically safe to use on the XJ.

Now, because of the lack of boost sensor on an XS11, and especially since on an 81, there's no wires connected to those boost sensor tabs, I would expect the XJ TCi to work and perform just like the 4RO Tci providing just Cent. Adv. adjustment, but not vac. adv. but the 4RO bike would have the mechanical vac. adv. and so might still perform adequately?

From what I've read/seen in diagrams showing the XJ's timing curves, they display separate curves for both the Cent. and the Vac/Boost curves, and so I would expect with no vac. sensor connected, the circuit would just not get any signal, so it wouldn't adjust the Vac. advance, but would still make the Cent. Adv. changes due to being able to sense the RPMs.

And so to further this mental masturbation exercise, because of the presence of voltage/POWER on those 2 wires/prongs on the 78-80 harnesses for the BR, I would be concerned about it causing problems with the XJ's boost sensor circuit, and would think removing the wires from the TCI plug would be the thing to do to get an XJ TCI to work on a 78-80 XS11...along with possibly also needing to swap out the PU COILS and reluctor parts....unless the XJ TCI can use the existing PU coils signals if they are within the same ohm range?? On a 78-80 XS11 if the PU coils could be used, would be to lock out the Cent. Adv. parts, but still allow the Vac. Adv. plate to work/move.

As I stated, not sure why someone would want to use/put an XJ TCI on an XS11 when it would be easier to either get a cheaper replacement 2H7 TCI, or even make one yourself out of AUTOMOTIVE parts....again probably much cheaper than an XJ TCI??

Phew....was it good for you, too?

[3Phase]

You're right, I know exactly what you mean and they're both rare so really it's not a good to idea experiment. I gave the TCI I pulled from my salvaged XJ to SoccerMike so I don't have it to check for clue and safety as I should before I go flappin' my soup-coolers.

That's good info about the 4R0 on an XJ with no Boost/Advance. I'm surprised it worked with the 'wrong' pick-up coils but that's one reason I've wanted a 'scope. I believe the XJ's 10M will handle the reduced voltage from an older, stock, XS11 ignition between the ballast and coils but the full 12V from a modified ignition with 3 Ohm coils like Accel or Dyna and no ballast resistor might kill it, I just don't know. I have seen apocryphal Google results that I can't find now from people that may have done it and lived to tell the tale but they could have just been trying to jack up the price on 10M ignitions.

The Black/Red Boost wire on the XJ11 is the one that signals the 10M TCI that the throttle plate vacuum is 0mm Hg with 2.0V ~ 2.4V or 200mm Hg with 1.6V ~ 2.0V. If it can handle the XS11 ignition voltage then it's always going to stay greater than 2.4V and the TCI will add no boost/vacuum advance, just RPM advance.

Now, why someone would put an XJ TCI on their XS?
An inexperienced owner may buy the wrong TCI or a mislabeled TCI.
It could be an emergency and it's the only one available.
"Hold my beer and watch this!"

[CaptonZap]

Scott, if you have a transistor catalog, you can look up the current capacity of a MJE5742G, which will tell you how much current you can run through the TCI before it melts the switching transistor carrying current through the coils. Each coil is controlled by one of those. They were the ones in the later model (1980) TCI. The earliest models had metal cased Darlingtons, and I don't have the number handy for those.
If I remember correctly, and being in my dotage, there is some question about that, I replaced the metal cased one with the MJE5742G's in a unit, and they worked just fine.

CZ

[3Phase]

I used to have some ignition transistors for an electronic ignition project I was working on for my old '71 GMC van. One weekend I saw a used MSD box and coil setup in the paper for less than it would have cost to finish my own ignition so I gave up on the project and ditched the Darlingtons.

[jwhughes3]

This picture is NO help because ALL 3 look exactly the same to me.

John

Electrically there is no problem and any XS11/XJ11 TCI will plug into the harness without leaking smoke but as T.C. and Greg said, match the ignition advance setup to the TCI, engine and cams.

The camshafts are the same for '78 and '79 with the 2H7 cams and from '80 to '82 they all use the 1980G 3H5 cams. Crazy Steve took pictures of the three different parts for a mechanical advance interchange guide:-


XS11.com Forums > Repairs > Interchange Guide: Mechanical Advances

[BA80]

Look here John...... http://www.xs11.com/forum/showthread.php?t=37189

[3Phase]

This picture is NO help because ALL 3 look exactly the same to me.

John

Thanks, Greg!

You have to click on the picture or the text to do the link-thing to the full explanation/thread, John.