Does an '78 XS11 engine fit in my '82 XJ11?

[rickmcdougald]

The title asks it all!
I've been offered a '78 XS11 that runs, but that's all. I'm thinking of replacing a run-out XJ engine with the XS. Can I do it?
All opinions are accepted.
Thank you,
Rick

[bikerphil]

Yep it will go right in, just switch over the components under the left side ignition cover and also use the XJ's alternator.

[rickmcdougald]

Hmmm 'a bit too vague. 'need more input ...

Dear bikerphil (and anyone else that's listening),
OK. But I need more details:
So you say that the engine suspension points will line up? How about the drive train, Fuel, air intake, and various controls (throttle, clutch, and electrical)? And there needs to be some modification of the electrical system? Which electrical system? Consider the electronic ignition and other "digital stuff" on the '82. How many other important things will need to be "migrated" to the XJ to make it a "whole" "daily rider" (like my beloved XJ is now)?
I'd like to seriously like to swap my '82 YICS-ridden engine for an real-life XS engine, so I need more input, please.
Has anyone of you out there done this?
What do you think, Andreas Weiss, TC, Big Daddy Funk, Bigfoot, CatatonicBug, dbeardslee, Incubus, jimboreeno, Ken Talbot, madbiker, malber, nashville_bill, olebiker, ratbyk, scoobes, trbig, TomB, and all of you whom have "been there"? What do YOU say?

I'm at the point where I'll have to lay some $ down. I want to make sure that this is an acceptable thing to do! You understand, Right?
Thanks Guys! I appreciate your input!
-Rick (The guy who has to do all the work!)

[crazy steve]

The motors will directly interchange, but there are differences. The alternator is one. You can swap the XJ unit onto the XS motor (it has a slightly greater output) or you can just plug in the XS regulator in place of your XJ unit. Which alternator you use makes little difference, but I will note that the XS unit has no wearing parts (no brushes like the XJ). The ignition is another difference; again you can swap your XJ components off that motor over to the XS and it's plug-n-play from there. Same with the carbs; the XJ carbs will fit right on.

Is that what you want to do? Well, that will present probably the least work, but there is a price attached. Remember that the '78 motor was the hottest of all the versions, and using the XJ bits will be a major 'detune' of the motor. If you retain the '78 carbs/ignition for max power, you'll lose the handlebar-mounted choke control and some rewiring of the ignition system will be needed (mostly just moving some wires in the plugs to the TCI if you swap to 3 ohm coils), along with the XS TCI. You will want to swap to 3 ohm coils as that reduces the ignition rewiring considerably. If you do use the XS carbs, the XS carbs have separate bowl vents that will need to be ran into the XJ airbox.

I will comment that if you decide on the using the XJ parts, I'd recommend swapping cams also. The '78-79 cams are considerably more aggressive compared to the '80-82 versions and there's been reported tuning issues when using the early cams/late carbs and ignitions.

Two other minor differences; one, the exhaust studs on the head for the pipes will be about 1/4" too long for your XJ exhaust. You can change the studs, or simply use some spacers under the nuts. Two, the XJ uses a 'low oil level' indicator (a float switch in the oil pan) and the XS uses a 'low oil pressure' switch. You can swap pans if you want to keep the XJ setup, or you can connect that indicator wire to the XS pressure switch.

That's it, everything else on the XJ stays the same. If you use the XS ignition, you'll have a couple of leftover wires (for the 'vacuum advance' sensor) that can be abandoned in place.

[rickmcdougald]

The motors will directly interchange, but ...

Crazy Steve,
Yes. I do intend to replace the XJ11's engine and ancillary components with the XS11's.
Thank you for all of the tips, tricks, and hints. 'sounds like it'll be a fun project for the upcoming Winter!
And Thank you, bikerphil, for food for thought.

Does anyone else have more info to add?

P.S. Andreas Weiss, Good luck in your fire-and-smoke-ridden area!

[bikerphil]

Good luck with your engine swap, all the help you will ever need is right here.

[TopCatGr58]

Crazy Steve,
Yes. I do intend to replace the XJ11's engine and ancillary components with the XS11's.
Thank you for all of the tips, tricks, and hints. 'sounds like it'll be a fun project for the upcoming Winter!
And Thank you, bikerphil, for food for thought.

Does anyone else have more info to add?

P.S. Andreas Weiss, Good luck in your fire-and-smoke-ridden area!

Hey Rick,

This sounds like a great opportunity for a tech tip! Please take lots of pictures, and feel free to make a write up about what ALL you change on the bike, and then post it, and we can make it a tech tip with you in the credits!

T.C.

[trbig]

There was a '78 motor in my XJ when I bought it. Everything XJ was mounted to it and it ran very well with XJ electronics and carbs. No YICS means easier tuning of the carbs.

As far as the alternator.. yes the XJ has brushes, but it also has the solid state stuff under the timing cover that you don't have to adjust or move. No vacuum advance to worry about wires breaking, no sticky advance bearings, etc... I've never wore out a set of brushes yet, so no idea how long they were designed to last.

As opposed to Steve's advice, I tried running those 78 cams in a later XJ motor I put in the bike and it wasn't good. I can't imagine that using the XJ cams on a 78 motor would be the best option either, but just a hunch. I would use the cams that go with the proper head.

[rickmcdougald]

I'd want to do a direct swap ...

I'd want to do a direct engine swap. If the XJ's points/alternator/electronics/instruments are better (and still work), I'll move those over too.
Easier to tune the carbs? I'd really like that!
Does the XS11 have the fuel-distributing/controlling Octopus? It works, but it's crazy to replace and route each of the lines.

Thanks everyone for your suggestions. Yes, TC, I'd document the swap! You shouldn't have to do all the work!

Note: I don't have the XS11 in my possession yet, but I'm trying ...
More later ...

[crazy steve]

I'd want to do a direct engine swap. If the XJ's points/alternator/electronics/instruments are better (and still work), I'll move those over too.
Easier to tune the carbs? I'd really like that!
Does the XS11 have the fuel-distributing/controlling Octopus? It works, but it's crazy to replace and route each of the lines.

'Better' is a relative term.... LOL. Remember than by '82, Yamaha was tuning these for emissions more than performance, which is why performance fell off as much as it did. The XJ ignition is 'better' in that it doesn't have the issues with broken pickup wires or failing vacuum cans, but it's initial timing/curves (all non-adjustable) isn't optimized for performance either, particularly with the '78-79 cams. And being a one-year-only system, parts are harder to find.

Yes, having the YICS gone will simplify carb tuning. As to the 'octopus', the 'E' doesn't have that, the same function is built into the petcocks. But those petcocks won't fit your XJ tank, so you'll have to retain the XJ bits there.

Tod, the major difference between the cams is the duration; the early cams have about 20 degrees more. Intake lift is the same for both, the late cams have more exhaust lift (but not that much more). Again, this was done for emissions, not performance.

[trbig]

Steve, I know with the early cams in my late motor, it'd run ok, but had absolutely no low end. Also, it was impossible to tune well since there was literally no vacuum draw at the carb boots when you hooked gauges up (Like maybe 2-3 hg's of vaccum?) and compression was down in the 90's. Swapped back to later cams and compression and vacuum readings went way up to normal.

[crazy steve]

Yep, with the increased duration that makes perfect sense. Those cams really need an aggressive timing curve to work right, which is what the '78 (and to a lesser degree, the '79) has. In your case, having the larger valves in the late head didn't help either. Yet another example of how well Yamaha did at tuning the 'complete package' (cams, ignition, breathing). I would expect that the XJ cams (with the XJ ignition) in the '78 motor would be a torque monster down low, have a very good mid-range, with it falling off in the upper RPMS due to the smaller valve sizes.

Using the '78 cams in the '78 motor with the XJ ignition would be roughly the same as the results you got, just not as bad because of the smaller valves. Now, how bad it would be remains to be seen, but I would expect a pretty good hit on the low end and midrange, with probably a boost at high RPMS. Whether or not he has tuning issues, we'll have to wait and see....

There's a reason that hot rodders after upgrading the intake/exhaust then switch cams and nearly all 'performance' cams have more duration...