XS400 '78 Frankenstein caféracer rebuild


XS400 Member
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Koudekerke, NL
After all my annoying questions here I thought it's no more then fair to annoy you all with my rebuild.

Please take in mind, it my first ever and I'm taking it slow. Baby-steps :)

After 8+ years of not riding I really started to get itchy to go out again.
So on the look out for something nice. Tried a bobber, hated it, so went for a caféracer thing which had a basis but could be adjusted to my wishes.
Found a XS400 close-by and tried it quick. Seemed to be sort of fine, so I bought it.
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Hated the tank and headlights, but it came with an original Yamaha tank.

Handed it over to my local shop for tuning and new tire and battery but it turned out worse then hoped.
Never checked (stupid me) but it ran on only the right cilinder.
So I made an appointment with a pro-tuner with Dynojet nearby and started designing things for the looks.
With the original tank (just for visual, doesn't fit yet because original mountingcups are removed) and seat a bit back:
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Much better!
Bought a lot of stuffses for visual and mounted new headlight, speedo holder, brake/rearlight (cheap one to test) and proper airfilters from DNA.
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(last pic: right the old filter...)
Found the right gascap, because tank turned out to be a Special model, with a slightly bigger gascap then the normal one.
I will go and strip, prime and paint the tank. But first set my mind on getting the bike to run.
I have no idea about motorthings, so I will need to get some help there.
Found an extra engine nearby for 100 euro, so I might go and buy that one for swapping parts.
My local shop is closed for two week, will go there first to ask about what he thinks.
If it's the valves, they don't come very expensive, so swapping those might be a good idea anyway.
If it is the piston it will be a pain, redrilling, new head an springs. Not looking forward to pay for that.

But in the mean time I have time to do small things non the less.
Working on cleaning the outside of the carbs, were painted black in a very ugly manner, so after the ultrasone bath the paint started to come of. Cleaning them all the way now, I want more silver/bare metal anyway on it.
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Left after ultrasone bath, right after grinding and polishing one of the two.
Done both now, now I have to clean the rest of the body, paint remover and a small brush will do the trick.

I'm sorting out the wiring at this time as well, it's a mess and cables are damaged so I want to do that neatly as well, under my seat.
It has electrical starter so I want to keep that one. So if I might end up with a new motor I have to swap those things as well.

Got a lot to do still, and going on a three week trip by the end of the month so I think I will be without a running bike until after the winter.

Question for now, on my batterybox is a regulator (it's called that right? with the fins?) and something else with wires running into it. Any ideas? It's not the thing where the thick + cable runs directly into.

I'm kind off leaning towards the M-box, but just not the price...

I have two inspirations:
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Last one found here on the forum. Have to see who's it is to give credit. Love that bike!
It’s from http://www.xs400.com/members/unleashedlive.11955/
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I'm taking apart the wiring atm. Step by step again, labeling everything where it came from.
I want to install the m-Unit v2 when all goes back in, and make a tidy wireloom.

I think I will always need the regulator, just figure out out where to put it in the loom in the end.

But question:
Whats this? And why is it here and do I still need it?
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So I will need both in the end, even with m-Unit I guess. The under seat pan will have to be a bit bigger then I guess. Thnx for the input!
You are welcome, from my reading I have come to believe the rectifier needs to be able to stay cool, needing some air flow. Just something to keep in mind. Some of the newer models can use combo unit reg/rec but I don't know of any for the older style
Thats great advise, I think I can mount them under the seatpan then, then they will get airflow.
I'm reading up on the m-Unit atm, figuring wiring out without knowledge is a lot of reading and youtubing :p
I have my recitifier completely exposed and mounted so you can see it. I like the idea of having some of the mechanical bits visible... kinda like how some bikes have the coils mounted on the downtube..

The voltage regulator you have is the same one my bike had before it broke. They are not too reliable but they work. Their voltage output can be very inconsistent and when they break it can fry electronics. I wouldnt use a lithium battery with one because they voltage output is not stable at all.

You can get a newer more relaible non adjustable regulator for the bike. You just have to do some very simple wiring. This is what i ended up doing.