Restore and Modify Motorcycle - 1981 Yamaha XS-400

I bought this non-running 1981 Yamaha XS-400 for a couple hundred dollars. Since Yamaha parts are widely available for this model, I knew it would be a low-cost way to get some 2-wheeled transportation. I restored it to working order and after riding it a few months, I decided to change some things I didn’t like about it, and maybe add a little beauty to the world. Every bike is different, but the solutions to the modifications I wanted can apply to other projects, or ease the fear of the unknown so someone else can take on a similar challenge.

The process to get it running involved cleaning and synchronizing the carburetors multiple times, replacing gaskets, cleaning out the gas tank, new air filters, battery, adjusting the valves, new brake pads, replacing the front brake fluid, new piston rings, cam chain tightener, new fork oil, and new tires. Total cost was about $700, the most expensive parts being tires and piston rings. There are other Instructables that go into detail for this part of the project. One cost I did not have to bear was painting the gas tank--a friend did it for free in their shop (thanks, Ralph!)

Then the problems surfaced. I rode the Yamaha in the stock configuration for a while, and found that I didn’t like the “cruiser” handlebars. The seat with the hump in it made me sit too far forward and since I’m 6’4”, my knees almost hit the handlebars. The heavy sissybar/luggage rack on the back made the bike look heavy and tired, even though it was very functional. The old shocks were weak and bouncy, so they had to be replaced. I didn't like the long rear fender, the old bulky lights, the big shiny gauges, and the exhaust pipes were rusty and ugly.

So here was the plan:

1-Replace the handle bars with wide dirt-bike handle bars to let me stretch my arms out more

2-Replace the seat with a flat seat, and remove the sissy bar/luggage rack

3-Shorten the rear fender

4-Replace the shocks

5-Replace the lights and turn signals with smaller units

6-Declutter the handlebars

7-Fix the rusty exhaust pipes

8-Other small details

Safety note: any time you make changes to a motorcycle, you may increase your risk while riding. Changes to the geometry are especially risky, so if you change the suspension or modify the seat or frame, be sure the changes don't impair the bike or make it handle worse. Changes to the lighting system can also make you less visible. Be careful!

Tools required:

Metric socket set

Metric box wrenches

Phillips head or JIT head screw drivers, large and small

Metal file

Drill and drill bits

Hacksaw 

Hand grinder with cut-off wheel (optional)

Soldering gun with flux and solder

Silicone grease (or dielectric grease)

Supplies purchased:

Replacement seat

Headlight

Front turn signals

Rear light/turn signal combination

Turn signal diode kit

Electrical connectors

The new bars had the same diameter bar as the old ones, so this was a straight bolt-on change. Remove then reattach the left hand grip, right throttle/hand grip, mirrors, levers and switches, then bolt down the new handle bars. Beware that if you also replace the seat and suspension, you may have to readjust the handlebars, along with the hand controls and mirrors, for safety and comfort.

(Also see: https://www.instructables.com/Changing-Motorcycle-Handlebars-Yes-its-that-ri/)

Most of these handlebar attachments used phillips-head screws. A comment about the phillips-head screwdriver: many bikes from Japan use a special type of phillips head, called a JIT. A regular phillips-head screwdriver will work, but doesn’t quite match the JIT cut, so the screw heads can easily get deformed after a number of uses. If you get a JIT screwdriver, you’ll find it fits more snugly into the screw heads, which makes even over-tightened screws easier to remove without damage. A nice addition to my toolbox.

I bought a generic flat replacement seat. My goal was to eliminate the old seat's 2-level feature. There are many sizes and styles available, so I had to be careful to find one that was wide and long enough. The new one was so different from the stock seat that I also had to make a number of modifications. The frame has a support that reaches up to support the rear upper level of the old seat, so I had to cut that piece of the frame to allow a flat seat to fit. (Caution: cutting any part of the frame can weaken the bike and make it dangerous. You have to be careful to restore the strength of the frame.) I don’t have a welder, so when I cut the seat-support piece, I left tabs on the main frame, then bent the cut-out piece to overlap the tabs enough so I could bolt it back on. This piece still serves its original purpose, but now it will accommodate a lower profile seat. Later, when I have access to a welder, I’ll have that little piece welded and eliminate the bolts.

After the rear fender was modified (next step, below), a straight bracket was bolted to the bottom of the seat with the 2 bolts that were already in the seat, and then a single bolt mounted to the bracket in the middle to line up with a hole in the middle of the cross-piece. After drilling a matching hole in the fender, that single bolt secures the fender to the cross-piece and the bottom of the seat. Note that the cross-piece holds the seat in position, but does not support the weight of the rider. The aftermarket seat I purchased had a series of rubber supports which support the weight of the rider. These rubber supports have to be mounted on the seat so they rest squarely on the frame. I just drilled mounting holes in the seat pan so they matched up with the frame, and used a tiny bit of silicone grease to help work the supports into the holes.

Lowering the seat support also lowered the fender, pushing it into the rear wheel. I cut about 4 inches off the front of the fender, the part of the fender that is near the swingarm. (Cutting chromed metal can be hazardous because chrome contains toxic chemicals. Protect yourself so you don’t inhale the dust.) I slid the entire fender forward to where 2 tabs on it happened to line up nicely with 2 tabs on the frame. With a little bending, I was able to bolt that end right to the frame. The middle of the fender was supported with a piece of ¼” aluminum stock bent to fit between the shock absorber mounting bolts. The rear end of the fender was a bit more complicated, since that mounting point also had to hold the seat in place. The hole had to be positioned so that it matched where the seat bolt projects through the frame cross piece. Finally, I bolted a small square of plastic to the front end of the fender to help keep dirt and water off the engine (a kind of reverse mud flap, a simple modification I’ve made on other bikes).

Relocating the fender gave me some more clearance, but the fender was still too close to the rear tire for my taste. I found a pair of shock absorbers/springs that were 2 inches longer than the stock ones, and after bolting them onto the existing mounts, I was satisfied. 

A couple of notes about shocks: (1) The old mounting bolts were 2-sided in that after the shocks were mounted, a second threaded bolt projected out to mount the luggage rack. I eliminated that rack, so I replaced the mounting bolts with regular bolts of the same size. Since these bolts must be very strong, I used automotive grade 5 bolts. (2) If you want to mount longer or shorter shocks, be sure to check the swingarm travel, and whether it can safely accommodate the new arc. Look for unintended consequences such as how it affects the path of the chain at its extreme ends, whether the chain or chain guard might hit another part of the frame, or if the tire will strike any part of the bike. 

In this case, the new shocks allowed longer swingarm travel, which resulted in the chain rubbing on the swingarm. Not acceptable: I didn’t want the chain causing wear on the swingarm, nor did I want that rubbing to damage the chain. I found a plastic chain guide called a "Motorcycle Chain Slider Swingarm Protector," that was made for a dirt bike. It rests on the swingarm so the chain rubs on plastic, not metal. I had to trim it and glue it to the swingarm with automotive emblem glue, and added a hose clamp for insurance. It sounds sketchy, but seems pretty solid, and I’ll be keeping an eye on it to see how it holds up. This is something that will have to be replaced from time to time.

The new turn signals are much smaller and less visible than the original factory units. This may make you less visible when you ride; be sure to consider this factor before making such a change.

All the wiring was intact, so swapping out the lights was mostly straightforward. The exception was the rear turn signals. The old ones were mounted on a pair of frame extensions that were built to hold the turn signals and the sissy bar/ luggage rack. I cut those frame extensions off, and bought a rear light that included the turn signal functionality. This was bolted right onto the fender, and I ran the wires through the existing wiring path from the original rear light. Cutting off the frame extensions created a few sharp edges, so I filed those down accordingly and painted the bare metal, then plugged the holes with black plastic plugs. Note that this bike uses a standard 12V electrical system. Not all bikes use 12V, so make sure you get components that match your electrical system.

The front turn signals were mounted on the forks, so I replaced them with similarly mounted, but much smaller, LED turn signals. When you replace turn signals with LEDs, the blinker unit can malfunction because LED bulbs offer much lower resistance than standard bulbs. One solution is to replace the blinker unit with an LED compatible unit, which is a simple swap. A further complication can arise if the turn signal indicator light is a single indicator on your dash. When I first tried the new turn signals, all of them blinked. So I first tried replacing the indicator light also with an LED bulb, but that did not solve the problem. After some research I found that the solution is to install an inexpensive "turn signal diode kit" in the circuit, between the two turn signal wires to the indicator light. (These kits are widely available.) Then the blinkers worked correctly.

These aftermarket turn signals and rear lights did not have connectors, just bare wires. I had to find connectors that matched the original wires and mount those on the new wire. The connectors are widely available, and while you can fasten them with some needle-nose pliers, there is a crimping tool available, which makes it easy to fasten a connector to a wire, See the instructable for “How to Make a Quality Crimped Joint.”( https://www.instructables.com/How-to-Make-A-Quality-Crimped-Joint/ )

The headlight was a simple swap. Removing the old light I discovered a large amount of wiring inside it. After pulling it all out, disconnecting the headlight wires, and reconnecting them in the new light, I found that you can stuff a lot of wires into a smaller light too. Just be careful about sharp bends in the wires and sharp edges on the light, secure any connectors, and insulate all parts of exposed wires, so they don’t short out. Test the light to make sure the low/high beam wires have been connected correctly.

Removing the big speedometer and tachometer was a matter of removing a series of nuts and bolts, and ending up with a steel bracket holding the bank of indicator lights attached to the triple tee. I decided to keep the indicator light unit (these lights are needed for state inspection) since it was a small black box and all the lights were neatly contained. But the steel bracket was way too big for my taste, so I fabricated a new, smaller bracket from ¼” aluminum. I drew the needed part of the pattern from the steel bracket, cut it out with a hacksaw, then bolted the new bracket onto the triple tee where the steel one was.

Mounting the new speedometer was a simple matter of fastening it to the other bolt where the old steel bracket was mounted. This speedometer connects to the existing cable but you can get speedometers that run off a magnet mounted to the wheel if you don’t want the thick speedo cable running down to the front axle.

I had hoped to replace the 2 header pipes with aftermarket 2-into-1 pipes, but none were available for this bike, so I repaired the existing pipes and reused the mufflers. The header pipe had a pin-hole where a previous owner had dented it, so I sealed that hole with some exhaust putty, then after it was dry, wrapped both pipes in pipe-wrap. (See also https://www.instructables.com/How-to-Wrap-a-Motorcycle-Exhaust/.) For the mufflers, they were in decent shape, so I kept them and painted them black, using high-temp paint in a rattle-can after sanding the pipes with 80 grit sandpaper. (See also https://www.instructables.com/Refinish-a-rusted-exhaust/.)

-I had the airbox side covers painted, but after putting it all together, I preferred the look of the exposed airbox on both sides, so I left them off.

-I made no modifications to the engine, so it still runs like an old XS-400, but is also still as reliable. 

-I also swapped the old boxy mirrors for some smaller ones--just a couple of bolts hold them on

After completing all these modifications, I’m pretty satisfied with how the bike looks. As for how it rides, I like the new seat because it allows me to sit further back on it with my long legs. But the shocks are too stiff, so it has a rougher ride than it used to. Of course, the old shocks were worn out, so it used to be bouncy and bottom out all the time. Now, if I gained 50 pounds, it would probably be just right. Something to look forward to!