1978 Yamaha XS400 Chop replacement thread.

[SaddleTramp98]

Im starting this thread to replace my other. if they ever get the missing threads back this one can be deleted or I may just use this one now. Heres my 78 Yamaha XS400. It's got around 2K miles and hasnt been on the road in about 40 years, hopefully I can change that.




I polished the carbs with Brasso then the carb bowls and top caps with 220 grit sandpaper up to 1200 grit, and polished them with Brasso. I then cleaned the carbs inside and out and changed the jets and lots of the internals. I also added some pod filters but I may change them








I got the bike running tonight I just used the stock jet sizes and settings for the stock airbox. It would idle decently but if I gave it gas, once it got past 2k rpms it would stall and die.

I'm gonna mess with it some tomorrow and see if i can get it to actually rev up and run steady. Then after I get my garage organized a little better and my tig setup for my welder I'll start tearing it down.

[SaddleTramp98]

Still working on collecting Tig welding supplies and my hardtail kit. I'm just thinking ahead and I ordered some parts since Lowbrow was having the 20% off 4th of July sale. I got some plug wires and the old style screw on metal ring terminals, a gas tank and some stuff for my other bike.

My bike has these coils with the plug wires built in...



They work but I need to switch to something else that can take my new plug wires and they need to either look good or be able to be hidden.

I'm running a points ignition. If I switch to an electronic ignition for my year bike, the instructions I read said you still need to run 2 single fire coils anyway so the whole placement/ looks aspect wouldnt change.

I think I read the Ohm's should be around 4-4.5 for the coils but I'll have to go back and do some more reading to check. What would running say a 3ohm coil do vs a 4-5ohm coil? I suck at math and I'm kinda new to wiring and electrical and points ignitions but I can learn pretty quick if I try. Sorry if these are dumb questions.

I was wondering if I could use any of these coils instead, the top 2 Dynatech's would be on a Harley I'd assume and the last ones would be found on Brit bikes. A coils a coil right?







Mikesxs also sells coils that are direct replacement but something better looking, better quality, easier to hide is what I'm after. But I can make them work they're black and the plug wires screw on them.

[TriNortchopz]

look here at available options:

Ignition: Systems, Coils, Plugs, Switches, Hardware

https://www.heidentuning.com/xs650-shop/electrical/ignition-systems-coils-plugs-switches-hardware.html

(check out their 880cc big bore kits while you are there...)

ya, looks like Mike has several options too;

https://www.mikesxs.net/motorcycles/yamaha/xs650/electrical-systems-and-batteries/ignition-systems.html

[SaddleTramp98]

look here at available options:

Ignition: Systems, Coils, Plugs, Switches, Hardware

https://www.heidentuning.com/xs650-shop/electrical/ignition-systems-coils-plugs-switches-hardware.html

(check out their 880cc big bore kits while you are there...)

ya, looks like Mike has several options too;
https://www.mikesxs.net/motorcycles/...n-systems.html

Those are for the XS650 though TriNortonchopz. I think the coils would work though they should be interchangeable as long as they're 4-5 ohms. I don't think the 880cc big bore would match up though, I didnt see too many threads on the xs400 forum about big bore kits besides custom stuff people have done.

I think I'm just gonna get 2 of these coils, and try to stash them somewhere, I just dont want a whole lot of wires showing looking like a big rat's nest.



Seems like not as many people working on the 400s vs the 650s. Mostly just cafe racers and drag bikes compared to all the XS650 choppers I've seen. I did find one thread that ended up being dead and unfinished, but this is kinda the look I'm going for minus the solo seat. I'd rather try to make a small king and queen seat or score one on ebay.

[mcknzAlex]

Looking nice, it seems like you are getting all the parts that you need.

[jervinLX]

Good info here. We'll be working on a XS400 soon

[SaddleTramp98]

After buying my FXR I'm pretty hit but I wanna get this project going again.

I've decided to go with drum brakes up front cause it's cheaper for me to piece together. Plus no master cylinder on the bars. If I need or want to, I will piece a disk brake setup later on if I come up on anything cheap.



Just gonna get something simple like this and a drum brake assembly off of Ebay.

I've gotta do some more research for a rear wheel with disk brakes that will fit the 20mm axle plates of the hardtail, and I gotta see if I can make a 530 sprocket work and how I'm gonna set up the brakes.

I also picked up a 2.1 gallon, mid tunnel peanut tank about a month ago. As well as some other things for it. I still havent bought my tig supplies yet but I will before winter so I can get my frame done.

[SaddleTramp98]

So theres a piece of a idle mixture needle stuck in the hole and it's pretty scratched up. So even if I do get it out I'm not sure it would work right cause it looks like the hole is bored out. So I may be buying some new carbs.

I'd rather weld up a manifold and run a single carb for looks and simplicity. I read on the XS forums about loss in performance, but as long as it wasnt going to damage the engine and the bike runs and starts good I wouldnt care. It's a chopper not a race bike.

[TriNortchopz]

I've gotta do some more research for a rear wheel with disk brakes that will fit the 20mm axle plates of the hardtail,

could be just a bearing swap using deep groove roller bearings with 20mm ID to increase options.

look here for axle sizes:

Axle diameter size list

Sorted by rear and front then size. Just find yours and you can see what else shares the same size for a swapping donor.

Jap Bike Rear Axle Diameters
20mm

https://www.dotheton.com/index.php?threads/axle-diameter-size-list.20952/

[TriNortchopz]

I'd rather weld up a manifold and run a single carb for looks and simplicity.

Thread: 2 into 1 intake single carb XS400 chop

"One of my favorite projects is the 2 into 1 intake. It was done for no other reason than I like the way it looks, and I like building...

The intake is made from a pre-made mandrel bent J 1.5" . I welded it together and coated the welds with JB Weld as a precaution, as aluminized pipe does not weld great. There are rings brazed that clip into the slots in the intake boots. The carb to intake boot is a plumbing fitting (don't tell anyone).

The carb is the stock unit with bigger jets and adjusted needle position..."

http://www.chopcult.com/forum/showthread.php?t=8684

[SaddleTramp98]

Thanks TriNortonchopz, I still have that link saved from when you posted it on the thread that got deleted.

I just have to go through and decide which wheel I want. I wanna find one that came from a bike that was made for a long span so it's easier to find but also a lesser wanted bike. From looking on ebay, a YZ250 rear wheel goes from $250-$350 while a Honda Cr250r wheel is about $100-$200 so I'd rather get a donor wheel from something like the latter.

I read that single carb intake thread you posted above, but after going back and reading on the XS forum some people on there were explaining how with the 180° crank the bike doesn't like a single carb. but I may go ahead and try it using one of my stock carbs to see how it does.

[SaddleTramp98]

Gonna be a slow build I'm working on building some high mids for my Sportster and still waiting on an air cleaner for my FXR, but I got my wheel last week and started taking the front end apart tonight. I did a little mock up just messing around.





No I'm not running these bars and probably not a rectangular light either. I got my eye on some pre-unit looking bars about the same height as the ones in the picture, and probably a cheap bates style headlight.

I'm gonna run a tall sissy bar and some pipes that line up with the height of the sissy bar and handlebars. Hopefully you can imagine what I have in my head.

When I get to the hardtail point I'd like to remove the gusset, like in the pic below and weld in a smaller one and add a crossbar with a motor mount on it. Id like to do some moulding on the frame too to smooth out all the hard lines. I still have to plan it out though.

[SaddleTramp98]

I was about to purchase the Voodoo Vintage hardtail for my bike. This is my first time hard tailing something so I wanted to keep it simple.

I assumed it was: slide it together, tack it, double check everything, 3 welds done. Like the hardtails for Sportsters and xs650's But after looking over the instructions you have to lay everything out, make sure everything is even, and assemble the whole thing pretty much.


So would it make sense to save $225 and buy this universal kit for $125 and assemble that instead?
I would just cut it to the same specs as the VV hardtail the bends may be a little different but pretty close. The universal doesn't have seat leg tube with it so I would have to make one

Unless I need a frame Jig then I'd just go with the VV kit, or should I just do that anyway? What would you all do?

[SaddleTramp98]

I ended up buying the weld on hardtail from Voodoo Vintage. It was easy and came in one piece like the Sporty ones do.

I welded it on and the frames been sitting around for about a year now I've recently started working on it again I cut the ugly gussets out of the neck and I'm gonna weld in a piece of straight pipe for support and weld the top motor mount to the pipe gusset/support.

I also took the calipers apart and there's some pitting on the pistons so I'm gonna replace the pistons and seals here soon. I'm gonna keep the stock mag wheels for now to save some cash and so I don't have to piece a lot of stuff together.

I've gotta finish welding some stuff and get everything mocked up and then I plan on moulding the frame, nothing crazy though.

I gotta get a set of carbs. There's a idle air needle broke off in one of mine and I don't think I can tune the bike to run very well on one carb. So I'm lookin at dual mikuni vm34's probably. Lots of ideas in my head for the bike.

Here it is in the rough.

[TriNortchopz]

I gotta get a set of carbs... So I'm lookin at dual mikuni vm34's probably...

found this:
"For the Yamaha XS400 we recommend the VM32 carbs for better torque and performance, even though the stock CV carbs are a 34mm you must allow for the area taken by the shaft and butterfly in the throat which consequently makes for a much smaller venturi than 34mm, which also has an air flow interruption factor. Going faster has never been so easy, say goodbye to hard starting, irregular idle, hesitations, and flatspots... The Dual Mikuni VM32 carburetor kit is easily fitted to your Yamaha XS400 and the improvement is instant..."

https://mikunioz.com/shop/yamaha-xs400-dual-mikuni-vm32-complete-carb-conversion-kit/?v=13b249c5dfa9

Carburetor Assy Kit - 32mm - Assembled - XS400 - XS Performance
$475.75

https://www.mikesxs.net/yamaha-xs650-xs-performance-carb-xs400-assembled.html

Got a motorcycle salvage yard around? a set of stock replacements would be cheap...could probably get a complete parts bike for the price of the aftermarket carb set...could even just the one side that you need.
found this:
EXCELLENT overview of the BS34 carbs on our bikes (while some of the specific jet sizing info may be off, in general this guide is amazing): http://drop.io/jn5sqkc

https://yamahaclub.com/forums/topic/19769-carburetor-options-for-81-xs400-and-other-issues/