If you're looking for a bike that won't break the bank but has tons of potential, a honda cm400t cafe racer is probably sitting right at the top of your list. It's one of those bikes that people used to overlook for years, thinking it was just a clunky commuter or a "beginner's bike" from the late 70s. But honestly, that's exactly what makes it such a perfect candidate for a custom build today. You can still find these things tucked away in barns or sitting in the back of someone's garage for a fraction of what you'd pay for a CB750.
The CM400T has a certain charm, but let's be real—in its stock form, it's a bit of a dork. It's got that "mini-cruiser" vibe with the stepped seat and the pulled-back handlebars that make you look like you're riding a lawn tractor. But underneath all that awkward 1980s styling is a bulletproof parallel-twin engine and a frame that's just begging to be chopped.
Why the CM400T is the Perfect Project
When you decide to build a honda cm400t cafe racer, you're stepping into a world where parts are actually pretty easy to find. Honda sold a boatload of these things between 1979 and 1981. The engine is a 395cc air-cooled twin that's famous for being incredibly reliable. It's not going to set any land-speed records, but it's got enough pep to make city riding a blast.
One of the best things about this specific model is the SOHC (Single Over Head Cam) setup with three valves per cylinder. It's simple enough for a backyard mechanic to pull apart without needing a degree in aerospace engineering. Plus, since it doesn't have a radiator, you don't have to worry about ugly hoses and cooling fins ruining the clean look of your build.
Dealing With the "Banana" Frame
The biggest hurdle you'll face when turning this bike into a cafe racer is the frame. Unlike the CB series, which has a relatively straight backbone, the CM400T has a "pressed steel" frame with a significant dip in the back. If you just slap a flat seat on it, the bike is going to look broken.
To get that classic, straight-line cafe racer silhouette, you're going to have to do some cutting. Most builders end up chopping the rear subframe and welding on a custom hoop. This is where the magic happens. By leveling out the rear, you can align the bottom of the fuel tank with the bottom of the seat, creating that iconic horizontal line that defines the cafe style. It takes some work, and you'll definitely need a welder (or a friend who has one), but it's the only way to make the bike look "right."
Choosing the Right Tank
The stock tank on the CM400T is a bit of a teardrop shape. Some people like it because it gives the bike a beefier look, but if you're going for a slim, aggressive vibe, you might want to swap it. A popular choice is the tank from a CB400T or even a CB450SC. These tanks usually fit the frame without too much drama and provide a flatter profile that flows much better into a custom seat cowl.
Whatever tank you choose, make sure you think about how it sits on the frame. Sometimes a little bit of shimming at the back of the tank can help tilt it forward, giving the whole bike a more "aggressive" stance, like it's leaning into a corner even when it's parked.
The Battle With the CV Carbs
If there's one thing that'll make you want to pull your hair out during a honda cm400t cafe racer build, it's the carburetors. These bikes came with Keihin Constant Velocity (CV) carbs. They work great with the stock airbox, but the second you try to put pod filters on them, the bike starts acting like a moody teenager.
CV carbs rely on vacuum pressure to lift the slides. When you remove the airbox and put pods on, you mess with that pressure. You'll likely end up with "flat spots" in your acceleration where the bike stutters and dies. You can spend weeks re-jetting and shimmying needles, or you can do what a lot of frustrated builders do: swap them for a pair of Mikuni VM30s. It's an extra expense, but the throttle response becomes so much crisper, and they are way easier to tune.
Wheels and Stance
Most CM400Ts came with "Comstar" wheels. These were Honda's early attempt at tubeless alloy wheels, and people either love them or hate them. Personally, I think they have a cool, retro-futuristic look that works well if you paint the "spokes" black and polish the lips.
If you're a purist and want wire-spoke wheels, you've got some work ahead of you. You'll need to find hubs from an older CB model that fit the axle diameters and drum brake setups. It's a lot of effort, but there's no denying that spokes give a cafe racer that timeless, 1960s London look.
As for tires, don't go too crazy with the "balloon" firestone style if you actually plan on riding the bike. They look cool on Instagram, but they handle like garbage. A good set of modern rubber in a classic tread pattern will keep you shiny side up when you're leaning into a turn.
Handling the Electronics
Old Hondas have a lot of wiring, and most of it is tucked inside that giant, ugly headlight bucket. When you're building your cafe racer, one of the most satisfying jobs is thinning out the "rat's nest."
Many builders move the battery and the components (like the CDI and regulator/rectifier) into a small tray hidden under the seat hump. This opens up the "triangle" of the frame, giving the bike that lightweight, airy look. If you're feeling fancy, you can switch to a lithium-ion battery. They're tiny—about the size of a couple of stacked smartphones—which makes hiding them a breeze. Just make sure your charging system is up to the task; old stators can be picky about modern batteries.
Making it Sound Right
A parallel twin can sound a bit like a sewing machine if you leave the stock mufflers on. For a proper honda cm400t cafe racer, you want a bit of growl. A 2-into-1 exhaust system is a classic choice. It lightens the bike significantly and gives it a punchy, aggressive tone. If you decide to go with shorty mufflers or "pipes," just remember that you're going to have to adjust your carburetors again. Backpressure matters, and these little 400s need a bit of it to run their best.
Final Thoughts on the Build
At the end of the day, building a cafe racer isn't about having the fastest bike on the road. It's about taking something mass-produced and making it yours. The CM400T is a fantastic platform because it's forgiving. It's a bike that teaches you about geometry, carburetion, and the joy of simple mechanics.
When you finally get that seat mounted, the clip-ons tightened down, and that twin engine fires up with a crisp bark, you'll realize why people love these bikes. It's not just a motorcycle; it's a machine you've rescued from being a forgotten commuter and turned into a piece of rolling art. So, if you see an old Honda twin for sale on the side of the road, don't walk past it. Grab some tools, clear out a spot in the garage, and start your own project. You won't regret it.