Once you choose your engine, the next step is choosing how original or modern you want the rest of the bike to be. Some builds reuse as much of the original CT70 as possible, while others replace the electrical system, controls, exhaust, and intake for a cleaner, more modern setup.

The YX70 is the easiest modern CDI engine to fit into a CT70 because it allows you to reuse many of the original 70cc components. It keeps the bike simple and familiar while giving you easier starting, modern CDI ignition, and a 4-speed semi-automatic transmission.

If you own a 1991–1994 CT70, you are in luck, you can swap this motor in extremely easily with our simple swap adapter harness. These later-model bikes already use a 12V cdi electrical system. However, this system is still half-wave (but it can be converted, an advanced topic for a later blog) and so you will still have that flickering headlight at idle running off regulated AC straight from the motor.

You can retain your original CT70 wiring harness, or one of our reproduction harnesses, using our YX70 breakout harness. This lets you keep the bike closer to original while adapting the engine to modern CDI ignition. You can also use one of our complete CT70 12V CDI lighting harness kits if you want a fully modern electrical system.

If you don't need full lighting, only plan to run a headlight, or don't mind adding your own circuits later, our basic harnesses are an excellent option. They keep the wiring simple, are easy to install, and are perfect for stripped-down builds.

The YX70 can use your original exhaust or nearly any CT70-style exhaust. We recommend a 70cc-specific exhaust because it's properly tuned for the smaller displacement engine and typically offers the best fit with stock engine guards and other factory-style components.

You can reuse your original carburetor, replace it with one of our reproduction carburetors, or upgrade to a Nibbi PZ18FL with an angled carburetor cap. You can use your OEM CT70 cap or purchase the cap from us. The angled cap allows you to reuse your original CT70 throttle cable and carburetor top cap for a clean installation. If using the PZ18FL, you'll also need a 2-inlet petcock to retain the factory reserve function while allowing the fuel to be completely shut off.

If you're using the original carburetor, one of our reproduction carburetors, or the Nibbi PZ18FL with your OEM cap or our angled cap, you can reuse your original throttle assembly or install one of our reproduction throttle assemblies.

If you choose one of our complete CT70 lighting harness kits, the included throttle is designed to work with the Nibbi PZ18FL carburetor without the angled cap and includes matching left and right handlebar controls. These controls will not work with CT70 handlebars that have welded-on lever perches. You'll need to grind the welded-on perches off your original handlebars, or replace them with perch-less fold-down handlebars or BMX-style handlebars and use clamp-on levers.

Another option is our BMC Pro Billet Throttle & Grip Set. It works well with all sizes of carburetors while allowing you to keep your original welded-perch handlebars, though the throttle will extend slightly past the end of the handlebar. It also works great with smooth, perch-less, or BMX-style handlebars as well so it’s a great all around choice for people who may want to upgrade or change components later.

You can reuse your original airbox for a stock appearance and quiet operation, or upgrade to one of our 35mm cone filters for a simpler build and increased airflow.

The 4 speed engine case and CDI system widen the motor, while it has relief cutouts on the side case, some foot peg setups may interfere with the shift shaft. You can space them down to clear, or run our heavy duty studded foot pegs and kickstand assembly. This assembly not only fits no problem, but it gives you a bit of leg room. Just be aware that the brake lever will also be pushed a little lower, which can be adjusted at the end of the rod no problem.

A 125cc or larger engine gives your CT70 a substantial increase in power, but it also changes what the bike needs around the engine. These engines use larger carburetors, wider crankcases, different exhaust requirements, and a modern CDI electrical system, so a few additional supporting parts are required.

For most 125cc and larger engine swaps, our recommendation is to update the bike with one of our complete 12V CDI lighting harness kits. They replace all of the original wiring in the bike, which is often old, brittle, or previously repaired. They also eliminate unnecessary connection points while providing full-wave 12V DC power throughout the electrical system.

If you own a 1991–1994 CT70, you also have the option of using our swap adapter harness. These later-model bikes already use a 12V electrical system, allowing you to swap aftermarket CDI engines while retaining the factory wiring harness. However, this system is still half-wave (but it can be converted, an advanced topic for a later blog) and so you will still have that flickering headlight at idle running off regulated AC straight from the motor.

If you don't need full lighting, only plan to run a headlight, or don't mind adding your own circuits later, our basic harnesses are an excellent option. They keep the wiring simple, are easy to install, and are perfect for stripped-down builds or race bikes.

You can also retain your original wiring using one of our breakout harnesses. If you're sticking with a kick-start engine, you have the option of keeping the bike 6V by choosing the 6V version. However, we almost always recommend converting to 12V by replacing the bulbs with 12V versions and installing a 12V flasher relay if the bike has turn signals. This allows the headlight to run from battery power instead of directly from the stator, giving you a brighter, more consistent beam that won't dim at idle while making the bike fully compatible with LED lighting and other modern 12V accessories.

A 125cc or larger engine requires a throttle designed for the larger carburetor.

If you choose one of our complete CT70 lighting harness kits, the correct throttle, left handlebar control, and right handlebar control are already included. These controls are designed for smooth handlebars or BMX-style handlebars with clamp-on levers and will not fit CT70 handlebars with welded-on lever perches. You'll need to grind the welded-on perches off your original handlebars, or replace them with perch-less fold-down handlebars or BMX-style handlebars and use clamp-on levers.

If you'd like to keep your original welded-perch handlebars, our BMC Pro Billet Throttle & Grip Set is an excellent option. It works with the larger carburetors used on modern engines while allowing you to retain your stock handlebars. The only compromise is that the throttle extends slightly past the end of the handlebar.

If you are trying to keep it all original as possible, we have had success opening the throttle tube of an internal throttle slightly to get more pull out of it and making up a custom cable to fit up to a Nibbi PE24FL, however we don’t normally recommend this.

We recommend using an exhaust designed for 125cc and larger engines so the engine can breathe properly and make the power it was designed for. Keep in mind that most 125cc+ exhausts will not clear the factory CT70 engine guard without modification. Our Kepspeed Warrior exhaust comes very close and can typically be fitted with a few spacers and minor adjustments while retaining the engine guard.

Modern larger cc engines have wider cases and no reliefs for the foot pegs upsweep like the original Honda engine, so the stock CT70 foot pegs usually will not provide enough clearance. If you don’t mind cutting and welding you can modify the original, however we don’t normally recommend it.

Our recommendation is use our heavy duty studded foot pegs and kickstand assembly. This assembly not only fits no problem, but it gives you a bit of leg room and a nice big pad to rest your feet. Just be aware that the brake lever will also be pushed a little lower, which can be adjusted at the end of the rod no problem.

We also have the option of a foot peg setup with a center stand. Makes them easy to work on, way more stable, but you lose some clearance and get a smaller less comfortable peg that bends upwards instead of away.

A 2-inlet petcock is recommended for all 125cc and larger swaps. It allows you to retain the factory reserve function while still being able to completely shut off the fuel supply.

The ZS125 High Output, ZS190, Daytona Anima 190 4V, and ZS212 4V should all be run with an oil cooler. We offer complete oil cooler kits for all of these engines, along with our custom oil cooler bracket for mounting the oil cooler to the valve cover bolts of the ZS190, Daytona Anima, and ZS212. Smaller engines can use the standard brackets included with our oil cooler kits.