Ryan’s Custom Planning: Monkey 125

     19 min read

    In a timeline non-exist, Ryan G. is busying tinkering his next project, a Monkey 125. He opens Photoshop and prepares to make a mock up concept. Ryan is neither an artist or a motorcycle custom master, but there’s one thing he is sure about: that he KNOWS what his dream Monkey 125 looks like. There are massive custom parts to choose from, like to equip a character with fancy gears in a MMORPG, Ryan balances the look, the cost, the performance, and the custom difficulty carefully, drowning in the sea of options. Hours passed, days passed, and months passed, and it is winter. Ryan feels cold and turns off his PC, “Maybe next summer”, he mumbles.

    Working on custom bikes is one thing, and designing a custom bike project is another thing. It can be very frustrating when you know what you want but there’s no product for it, or worse yet, it does exist but you just can’t find it. Planning a custom bike project is the most exciting yet exhausting stage of motorcycle customizing, this article is NOT intended to be a custom guide of Honda Monkey 125 or something that trying to make you buy from Webike, but rather a guide of how to efficiently design and plan for a custom bike project. In this article, I pick a Honda Monkey 125 as an example. Why? There are reasons and you will need to ask yourself the same before committing buying a donor bike.

    Reasons of why I choose a Monkey 125 as my project:

    1. It’s relatively cheap yet with modern technology like fuel injection. That means I don’t have to adjust the carb and air/fuel ratio, can still have access to most OEM parts because it’s a newer bike, can save & dump my money on more fancy custom parts, and modern bikes are just more reliable in general. Also, being a small cc bike means custom parts are cheaper. Yeah, call me a cheapskate, I will take it as an compliment, thank you very much.
    2. It’s lightweight. If you want to tweak or paint the engine or frame, it’s very important to remember. Your friend is not always there to help you lift a 200 lbs. inline four engine. A single cylinder is also easier to work on.
    3. It has a good range of custom parts to choose from. Not as many as the old Monkeys (the Z50’s) but still a fair amount.
    4. I love this minimoto after all.

    I’m not saying that it can’t be done with a CB750, a Z900RS, or even a Goldwing, it’s all personal taste. If you want to tinker something big, go for it. It’s your project after all. Once you got all the questions straight and convinced your wife successfully, let’s start the planning process.

    1st stage Planning: What do you want?

    What is the ultimate purpose of your project? Will you going to ride it around, or just want it to look cool? Are you taking it to bike shows or selling it for good money? The purpose defines where your project will emphasis on these three segments: Performance, Uniqueness, and Cheapness. The trio can be co-exist, but unless your last name is Zuckerberg, it is be wise to choose which one is your favorite child.


    First thing first, you will never get close to modern bike performance if your donor bike is an older one, period. Motorcycles have evolved fast during the past decades, even though you can put those sweet and cool looking GSX-R forks and wheels on it, it doesn’t mean you will get the same handling. A lot of donor UJM bikes come from (usually) 80’s, and they are not designed to be ride hard. The frame and suspension are usually soft, forks are not as beefy, brake calipers and rotors are not as good. However, with some decent priced upgrades, they can be a reliable around town bike while still look cool.


    Every custom bike is an one of a kind, but they are more or less toward one of these categories: Cafe Racer, Scrambler, Street Fighter, Bobber, Flat Tracker, Racer Replica, Rat Bike, etc. You can keep on adding styles to this list, or you can mix two or more categories together or create your own. In this article, you can see how the bike owner mixed scrambler style with a pair of springer fork, making it a real unique bike. Generally speaking, the more uniqueness the bike has, the more it will hurt the performance (not absolutely, but in most case yes). Balancing between an unique but crappy ride and an decent ride yet average Joe looking is a problem one has to conquer.

    Yep, that’s a Monkey 125


    How much you want to spend on your project? Set your budget and add 30% more to it, now that’s more like what you are going to spend. The truth is you will spend more than you planned, including special tools, paints, pay someone for doing the job you don’t know how to, and new parts that actually work. You will generate new and better thoughts during the custom process, and it’s itchy not to do it. In general, modern bikes and small cc bikes will have relatively cheaper options, and the older and rarer the donor bike is, the more investment is needed.

    So… What’s the plan?

    Enough talking and let’s do this! Just my way of doing this, but I will divide the project into 5 steps:

    Mock it up

    Your bike might look like Frankenstein during the mock up but don’t worry, just get an idea of how it’ll look.

    Use Photoshop to mock up the completed form of the project first is a great move to do, it provides you a general image of how the bike is going to look like when finished. Ask somebody knows how to do it if you don’t. Put all the visible custom parts on the bike, suspensions, wheel, tire, handlebar, headlight, number plate, stickers. If you are planning to do a custom paint job, it’s time to design how you are gonna do it. In this project, I will turn the Monkey into a scrambler, therefore I will try to put on a higher seat, bar risers, spoke wheels, better suspension, and a skid plate.

    Make it run

    Won’t be a problem with modern bikes, but if you are cheap (like me) and put your eye on some old junkie, this is the first thing you want to make sure before you buy. Does it crank? How’s the compression of the engine? Is there spark? Any sign could indicate a failed engine that need overhaul. For older bikes, check the electric system first as they are prone to fail. Next, check if there’s any oil leakage, it could be the gasket. Then give the carb a thoroughly clean, put in some fresh gas, hook up a battery charger and try to start it. If it will start after a few try, it’s usually a good sign of a restorable bike. The engine must be runnable.

    In my case, the Monkey 125 is still a very new bike and doesn’t need any care. However, I’d like more juice from that air-cool 125cc engine, so a big bore kit is the way to go. I’d choose the SP Takegawa 181cc S-Stage N-20 Big Bore Kit,probably the best kit on the market to custom this engine. On a carb bike, you can tweak or replace the carb to get better fueling for a big-bored engine, but since the Monkey 125 is fuel injected, hence it needs a new fueling unit like the Power Commander V. Another option is also what SP Takegawa recommended: FI Controller Type-E. The PCV is a long loved brand and the pinnacle of aftermarket fueling module, the adjustability is superb, they are tested to prove its success. On the other hand,  the SP Takegawa one might not be as fancy or trusted, but they surely know how to tune their own kit – the FI Controller Type-E offers several fueling maps specifically for SP Takegawa big bore kits coming in different sizes. That means it’s a plug-and-play solution that users don’t need to mess with the mapping. Both come in close prices and in this case, I’d like to choose the SP Takegawa one.

    The throttle body can be replaced with SP Takegawa Big Throttle Body Kit to extract even more power but I decided to skip. With 181cc bored engine, the little Monkey 125 will provide enough fun power for me and also I can save some lunch money for more custom parts.

    Make it stop

    If you are trying to restore an older biker, chances are the brakes are pretty weak so you want to make sure the brakes can stop your bike efficiently. You have several options like: bigger, better, newer brake rotor, overhaul the brake calipers with new piston and seals, stainless steel braided brake hose, brake fluid flush, new brake pads, or better yet, get some brake calipers from modern bikes with a compatible mounting bracket. Overhauling a brake caliper is not so hard to do and can help you to understand how it works. Also make sure the brake hose’s length is matched should you change your brake lever’s position, too long or too short of a brake hose will result a crappy brake work.

    The Monkey 125 has both front and rear disc brakes that are working great so no need to tweak those. I thought about using a stainless steel braided brake hose to reinforce the brakes but that’s not really necessary as scramblers are designed to be running both on/offroad.

    Make it turn

    The project has to be able to finish a satisfying turn, that’s all motorcycling is about. Depending what style of a project bike you want to achieve, clip-on bars or straight bar? Your call. They both work and are just one aspect affecting handling. Check your stem bearings, can you turn the handlebar smoothly? If not, it’s a sign of rusted stem bearing and that need to be replaced (ideally with the races). How about the tires? Choosing the right tires for the right job is also essential, not to mention that different types of tire provide different style to the bike. Is there any leakage from your suspension? Replace the seals with fresh suspension oil. So many custom parts can be used to make your bike a fun ride, check out our quality selection of suspension components.

    Now back to the Monkey Scrambler project, I’d like stiffer suspensions like the Kitaco Front Fork Spring for Monkey 125. They are affordable springs that are stiffer than stock in case I bottom out the forks running offroad. Additionally with Asahi Plating Front Fork Cover to protect my seals and fork tubes getting damage from dusts and rocks. For the tires, the original Monkey 125 has block tires but that’s not enough (or cool enough) for a scrambler, I like those small knobby tires on 12″ wheels so I pick Shinko F504 and R505 for this project.

    Make it cool

    OK, the final stage and the most important stage of planning a project. We all want our bike looks like a true badass, and how to achieve that goal is completely subjective. Side mounted number plate, take off the headlight unit and make a custom fit, custom paints with stickers… sky’s the limit.


    Planning a custom bike project is exciting and yet needs massive amount of time to draw a big picture. Even with a detailed plan, the project can still have drastic change 180 degrees, but that doesn’t mean planning has no use: it will give you a general idea what the completed bike will be look like, it will help you to decide your budget and pick what custom parts will be used for the project, and it helps to generate even more idea during the planning process.


    Ryan G.
    Ryan G.


    Ryan G.

    Nationality is unknown, Ryan is an experienced rider and custom bike builder, spending most of his time in garage trying to make things work. He rides, he writes, and he misses In-n-Out.