Rookie Bike Build


XS400 New Member
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Iowa, United States
Hey everyone!

It's been a long time coming for this post. This is my first ever build, so there may be a few cringey rookie mistakes, but that's nothing a little swearing won't fix! After all the help with countless issues on my bike, I felt that it was the right time to upgrade from lurking to an actual post.

The beauty is a 1977 XS400D. I bought it in August 2016 off of craigslist not running (I've been lurking a while...whoops). As I would find out later, it was somewhat neglected and needs some TLC. When I bought the bike, I make sure that it turned over and had compression. At the time, I didn't know about this forum, so diving in reckless to an entire engine rebuild seemed ill advised.

A carb rebuild was the fist order of business, and, with the help of the technical info posted here, I avoided really messing them up. I got lucky that the diaphragms were intact because those things are damn expensive, yikes! The rebuild kit I used was the Keyster Carb Kit for the 400D. Each one runs about $20, but they include a good amount of parts. I went with the shotgun approach to rebuilding the carbs and replaced pretty much anything I could find for a good price. In the end though, I believe that only the main pilot jet would've fixed it..... I don't think the PO knew that running a steel wire through carbs is bad for them, but I'll let the result speak for itself:
If you were wondering, yes that is a giant gouge by the pilot jet, and someone had never hear of JIS heads, because a phillips did a number on the butterfly valve screws. I'm no engineer, but my bet would be that a rough cut into the pilot jet isn't good for laminar flow. Oh well, as long as the bike isn't under 4k, I'll be good to go (fast)! Even with the damage to the carbs, the rebuild kit did the trick and she lived! I took a victory lap around the block with a lot of backfiring and low power, but still power. Once I knew it would run I promptly disassembled her and had to head off to college for the semester.
...3 months later....
After thinking about it for all of fall semester, I was finally able to finally start the full disassembly process in December.
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With my luck, the garage was about 0 to 10F ( -15C) that week, so the "warm" glow of those heaters did very little. Oh well, a little frostbite never hurt anyone. Anyway, I made sure to meticulously tag and bag every little piece so I could get it back together next (this) summer.
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While taking the baby apart, I noticed that the area under the pivot point for the sway bar had completely rotted out, which is no bueno. While It wasn't a huge issue, with only double shear going to the pivot, I still wanted to ensure that it didn't deform the right side and throw everything in the back off. Going in with the death wheel (angle grinder), I cut out all of the rot and filled it with brand new some rebar... whoops. I'm a terrible welder. At this point you're probably thinking: "Wait where did the paint go?" well that adventure is next.
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death wheel..Death Wheel..DEath WHeel....DEATH WHEEL!!!
Time came to slice and dice the unneeded parts on the frame for aesthetic purposes. I could feel all of the cringing designers as the grinder make quick work of the end of the frame. After the hacking, all of the old paint, along with the surface rust had to come off. That was a job for the $5 auction sand blaster and some play sand. I will say, sandblasting in December in your front yard in a winter coat gets a few odd looks from the neighbors, probably out of jealousy for the sick xs400 frame! I digress. With the frame and fork all sandblasted they were ready to go off to powder coat. With that, I headed off to university once again.
....another (really long) 3 months later...
May 2017, time to get serious about knocking the project out! Before anything, I had to step back and admire the shiny powder coat...Must. Not. Get. Distracted. From. Build.....ahhhhh. Ahem, Anyway, I went through and mated the engine back to the frame by tilting both on their side and affixing a few bolts before tilting back right side up (sorry no pictures because my nonexistent muscles were maxed out) Before this, the engine got a good polishing with 200, 400, scotchbrite, superfine steel wool, and some mothers polish, in that order.
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The wheels and forks needed to get put on so I could wheel it around the garage that's not mine. With one look at the sprockets, I decided, with the help of the forum, they needed replacement. Apparently shark week isn't as appealing when talking about sprockets, yikes! They were replaced to a ratio of 17-37, from 16-37. I'm a smaller person, so I felt the less torquey ratio could be justified, plus less wear on the engine sprocket. The wheel bearings were also checked, wheels cleaned, and painted. Attaching the fork to the frame was a little more difficult than anticipated with the bike being on a dolly and facing down. The solution was a little, uh, creative, but I figured that 2x4s are a pretty standard shop tool. Yes, I know the handlebars are upside down; I had limited vertical space when it went in storage for the night. The rest of the assembly was pretty standard, no pictures, since it's in the manuals, sorry.
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Okay... by standard I meant all of the non modified things, this is where it gets fun and we can break some rules! First on the agenda, the electrical box. The materials costed about $10 here in the US and consist of sheet metal and your choice of paint. I wanted something that would blend into the frame, but still be big enough to hold a powersport battery. It's 2" (+/-5cm) deep, so 4" with the frame and stock seat pan, more on that later. The brackets for the pan mount onto the existing grommet mounts on the frame that were originally meant for the cover. It's secured by the two middle screws. I went with a cheapo battery with 3ah and 50cca, which I found out later barely cuts it. Fair warning: if you have ocd about messy electrical stuff, looking at the last pic may be bad for your health. Finally if anyone starts to worry about toasty electronics and an unwanted seat warmer, it's all good, knock on wood, because the rectifier is mounted under the box. If anyone is interested, I'll be happy to upload the full final designs with dimensions for the box.
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Welp, turns out I exceeded the number of attachments for a post, so I'll continue this in part two. Just a little snippet: I'll go over making the stock seat pan into more of a slimmer look, troubleshooting ignition, rererebuilding the carbs, firing her up for the second time, and future plans. If you've made it this far good luck dealing with my B.S. for the rest, because it's all downhill from here!


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Here's part two:
I wanted to use the stock seat pan because it fit the battery well, also college isn't cheap. The back of the pan was cut down to be closer to level with front for more of a "cafe" look. All of the existing paint and surface rust was ground off, and a new coat was put on. The foam cutting method was slightly unorthodox, but far cheaper than buying the stuff, and fit the pan better. By far the hardest part of the seat build was learning to sew. I wanted to do a cross stitch pattern on the seat, but the sewing machine couldn't hang, so I settled for the horizontal lines, which I'm happy with. Between the existing foam and the vinyl, there's a layer of 1/2" foam to even out the machete marks. (that's a sentence I never thought I would say). The vinyl was then attached to the pan using the existing points stamped out of the sheet metal. If anyone wants more details I can get pics of the bottom of the pan.
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On this build what really killed me was the electronics. I wanted to keep almost everything stock, as the engineers had designed it in 1977, because I guarantee that they know a lot more than I do. In all honesty, before this build, my understanding of electrical systems fell somewhere between dark magic and women. After extensive lurking, and going through the system about 5 times I finally got it The major issue for me was all of the components that were grounded to the frame. Since my frame was powdercoated this was the problem I cut my teeth on for about a week until figuring it out. The condenser is what really killed me, picture of the filed area in the frame below. I still had to shed a tear inside when any part of the coat had to be filed off for an electrical ground . My main takeaway, is to read the manual and left is orange, right is grey. I switched that a few times also.
With the rebuilt electrical system, I tried, with no luck, to fire the gem up. Obviously, I thought, the carbs would be the issue, granted they were dry all winter and indoors, but denial is fun. So I went about rererebuilding the carbs with the knowledge that a year of lurking gives. Surprisingly, after finding out the manuals are helpful and following them to a T, the carbs went back together in no time. The butterflies were bench tuned with two pieces of paper and all the proper adjustments made. I reset the floats at 26mm, WHICH IS NOT WHAT THE MANUAL SAYS, because 32mm is ridiculously high. Haha, I thought I was going crazy for about an hour looking for the 26mm info. This thread saved my ass. The pilot jets were both turned 1.75 out in the end, which I will likely retune when the bike is warm. Also, I havent synced the carbs yet, so my bet is that the gouged one is likely running rich and needs to be evened out.
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With the rebuild, I thought for sure all of the gremlins had been worked out....nope. Tried kicking it over and nothing. the spark was good, carbs good, so I narrowed it down to timing, which brings us to tonight. Using the same paper method, making sure the points released the paper at LF and RF I timed the bike, hoping that it would finally run. Again, a whole bunch of nothing. on a whim, I checked over the ignition wires, and of course they were reversed. After switching orange to left and gray to right she fired on the 4th kick! Victory! here's how it stands as of tonight:

So now what? Well my next plan is to build the air filter so both of the carbs are fed out of the same pod. It's more of a concept right now, but the math for laminar flow is looking pretty good. I also want to consolidate the existing analog gauges into one cluster. I have the designs, but wanted her running more than I wanted aesthetic right now. I'll also update the turn signal relay to work with the led taillights, work on the mufflers (likely cut down and wrap), and update the brake lines. Here's some teaser pics:
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All in all, this forum has been an invaluable resource to me while working on my build. If anyone has any questions about methods or wants more info, I'll be happy to help and hopefully add to all of the knowledge.
I have some concerns about the pilot mix screw hole in that one carb you showed. It looks like the tip of the screw has broken off in the body and someone has tried to get it out. Make sure the tip has not broken off in the other one also. I posted a pic of what the hole should look like.
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Hi Chris, Thanks for the input on the pilot jet. Yeah, that was bugging me quite a bit when I tore it apart too. Looking at the old needles, it does appear that one broke off, like you suggested, and the PO dug it out. Before putting the new pilot needles back in, I double checked that the passage was clear with a stethoscope. The bottom was a fairly gouged and looked almost like there were two ports instead of 1. I zoomed in on the picture and drew arrows to the possible "two" ports.

The piece that looks like a lodged needle, is some pushed over aluminium from the carb body (still not ideal). With the carbs running pretty well currently, is there anything I should watch out for with damage like this? Right now, she starts first kick, and there's no backfiring, the power hasn't been tested yet though... I'm planning on syncing the carbs sometime in the next week. Since the pilot jets only operate under 4k, would it work to do a carb sync at lower revs with the pilot needles, then go past 4k and check the butterflies?
Carb syncing should only be done at idle with the bike fully warmed up. Use a manometer for this.
I finally got around to syncing the carbs tonight. The manometer and fittings are a bit makeshift, but when most hydraulic/pneumatic fittings are in freedom units, what do ya do. I actually ended up drilling through two 8mm fine threaded bolts to fit into the carb bowl drains, then fixed the 1/4" tubing by press fit and zip tie. Lucky, there were no leaks and it needed a surprisingly small amount of adjustment. I used ATF fluid for the liquid, but considered using something less viscous for more accurate pressure measurements...possibly something fun for the future.
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You synced the float bowls????

The vacuum connections are on the carb boots, between the motor and carbs and on the other side of the butterfly plates.
There's nothing significant to measure at the float bowls... They are wide open to atmospheric pressure.