CDI Swap

[jfgood]

Can i swap the CDI from a XS into a XJ will it work ?
how hard is it to find a used XJ CDI

thanks

[crazy steve]

Short answer, no...

The '78-80 XS used the same TCI, the '81 was a one year only part, and the XJ is different from both.

The difference is the '78-80 bikes used a mechanical advance unit along with a mechanical vacuum advance. In '81, Yamaha moved the 'mechanical' advance into the TCI (but retained the vacuum advance), then for the XJ they moved both functions into the TCI (using a vacuum 'switch' to add advance via electronics). There's several other differences between the XS/XJ ignitions, enough that no parts will interchange.

It is possible to install the '78-80 ignition on the XJ, but you'll need to change everything except the coils; add the mechanical advance, swap to the early pickup coils/vacuum advance plate, TCI, and timing cover. The wiring plugs in the harness are the same (a bit of luck), but you'll need to verify if the pin positions are the same.

[jfgood]

Thanks for the info sounds like a pain to do the swap . I have a XS with no paper work
and next week i will be getting a XJ with paper but bad CDI .The motor and trans are good
in the two bike so i need to do some swaping around to get one good bike . what to do ?

[TopCatGr58]

Hey Jf,

Yeah, lots of questions to ask yourself. What year is the XS, and how many miles on it vs the XJ engine? If it's one of the earlier 78 or 79's with low miles, those engines are stronger than the XJ's due to detuning for emissions with the XJ.

But the XJ has a stronger charging system, and needs that for all of the electronics it has/uses vs. the XS, and since the XJ is papered, it would probably be easier to swap the ignition components from the XS to the Xj engine, rather than swapping the entire XS engine! The XJ's carbs still use the #2 carb vac. adv. port that you will be able to connect to the mech. vac. adv. pot vs. the Vac. Sensing box that is under the tank. And this way you get to keep the stronger charging components of the XJ.

The earlier XS's ignition system used a ballast resistor for the ignition coils, but the 81 and 82 XJ don't, their coils are 3 ohms, so you'll want to keep the XJ ig. coils. I can't recall the exact pinouts for the XS's TCI(transistor controlled ignition)...it's not a CDI..(capacitance discharge ignition), but there are 2 ignition coil power circuits....one that is powered during starting which bypasses the XS's ballast Resistor, and then 1 that is powered once it's running which routes thru the B.R. via the XS's harness. The XJ's TCI sends the full 12 volts to the coils all the time, so the harness will probably NOT have wires going to the pinouts for the starting coil power pins.

As an aside, the 81 TCI "Can" work in the XJ, because it does have the cent. adv. timing curve programmed into it, which will give you plenty of power, but you will loose the vac. adv. curve which provides more adv. for low load "cruising" type running which helps save fuel! A member posted about doing this swap, and his bike runs fine with plenty of power, and I don't think he posted much of a mileage drop....but I don't think he "cruised" it much!

However, the 81 TCI's are almost as rare as the XJ's because they were only made for 1 year, like the USA's XJ....but the XJ was made for 2 more years for Canada.

Good luck, hope you get a working bike out of it before the riding season is over!
T.C.

[jfgood]

Topcat i am sure the XS is a 79 32000 ks on it I just picked it up this week cheep
no carbs or paper work . the XJ will come later nexted week have not had a look at this bike yet the owner says it was running good till the TDI quit he says it is running on 2 cylinders i will find out more when i get the bike i also have a 3rd motor that i think is early XS . not sure how i keep finding this stuff but haveing fun so why not . My riders are
84 XJ low ks and a 86 Concours so got the summer covered

[ag9123]

XJ1100J Maxim TCI

I have a brand new never used Hypertek unit for sale on EBAY if you're still looking

http://www.ebay.com/itm/251068452438...84.m1555.l2649

[WMarshy]

Topcat i am sure the XS is a 79 32000 ks on it I just picked it up this week cheep
no carbs or paper work . the XJ will come later nexted week have not had a look at this bike yet the owner says it was running good till the TDI quit he says it is running on 2 cylinders i will find out more when i get the bike i also have a 3rd motor that i think is early XS . not sure how i keep finding this stuff but haveing fun so why not . My riders are
84 XJ low ks and a 86 Concours so got the summer covered

You might just get lucky, sounds like a bad coil to me. I dont think you would have any cylinders firing if the TCI was bad.

[Axel]

Tci

A typical TCI failure is the loss of 2 cylinders . Either 1 and 4 or 2 and 3 indicates an ignition system issue . A series of tests can eliminate everything up to the TCI . A 81 4RO TCI can be adapted for an XJ in a pinch . I have just had my first success in reviving a XJ TCI by reflowing every solder joint on the board . Thanks to the ppl here .

[CaptonZap]

And for those that do not have any luck reviving their's by resoldering, let me know.
I am set up to do more intensive surgery on the '78 to '80 TCI's.

CZ

[jwhughes3]

Could be a broken pickup coil wire. Same symptom running on only 2 cyl and way more common than TCI going out.

John

[MaximPhil]

Or a wet coil or loose wires into or out of coil.
Phil