Yerf Dog go-karts were extremely popular in the 1990s and 2000s, with more than 20 million units sold. Although they aren’t in production anymore, you still see quite a few of them around.
Depending on the engine specifications, a Yerf Dog go-kart has a top speed that ranges between 20 – 35 mph. If your Yerf Dog is equipped with a Tecumseh 5 hp or 6 hp engine, chances are that it maxes out at about 25 – 30 mph, whereas the 7.8 hp engines will peak at about 35 mph.
What if I told you that there are ways to make them even faster! That’s right, you’re able to increase the top speed of your Yerf Dog go-kart through methods that I will teach you in this guide! So, let’s get to it!
1. Upgrade the Engine
The most significant and effective change you can do to your Yerf Dog go-kart to increase its speed is to change its engine. The engine is responsible for powering your Yerf Dog and upgrading to a more powerful engine also means that you increase the overall output.
Yerf Dog go-karts are powered by a Tecumseh engine (it’s the stock engine) that has an output between 5 to 7.8 hp. The engine type and output are determined by the type and size of the go-kart. Here’s a list of all Yerf Dog engines for reference.
To summarize, here’s a list of the engine and their respective models:
- Tecumseh 5 hp (1203, 1204, 30009)
- Tecumseh 6 hp (3002, 3200, 3202, 30021, 30032, 30033, 30034, 32001)
- Tecumseh 6.5 hp (3203, 3205, 3208)
- 7.8 hp (3209, 42101, 42105, 32092, 32093, 40000, 42054, 42094)
Upgrading to an engine with greater output (more horsepower) will increase its top speed. However, you’ll need to make sure that the engine has the right specifications and also physically fits on your Yerf Dog.
Before selecting a suitable engine upgrade, consider the following:
- Weight of the engine
- Width of the engine
- Height of the engine
- Crankshaft diameter
- Shaft type (vertical vs horizontal)
Engine Upgrade Selection
The best engine upgrade for your Yerf Dog depends on your preference. I suggest that you aim for about 20% – 30% more output. This would mean the following:
|Stock Engine||Target Output|
|Tecumseh 5 hp||> 6 hp|
|Tecumseh 6 hp||> 7 hp|
|Tecumseh 6.5 hp||> 8 hp|
|7.8 hp||> 10 hp|
2. Optimize the Carburetor
A go-kart carburetor is a mechanical device that mixes air and fuel before it’s injected into the engine. Having the correct air-fuel ratio allows for optimal combustion inside the engine, increasing the output and ultimately making your Yerf Dog faster.
There are two different types of carburetor adjustments, however, only one of them can increase the top speed of your Yerf Dog. Below, you’ll see a short explanation:
- Air-Fuel Adjustment – The pilot screw allows you to adjust the air-fuel mixture to an optimal ratio. This allows you to increase or decrease the amount of air and fuel that your engine receives.
- Idle Adjustment – The idle adjustment is for setting the engine idle speed and does not affect the top speed. You should skip this.
I’ve created a complete guide on how to adjust a go-kart carburetor where you’ll be able to follow a step-by-step guide to ensuring that your engine receives the right air-fuel ratio.
3. Re-Gear Your Yerf Dog
Re-gearing your Yerf Dog go-kart can also increase top speed. Your Yerf Dog has two sprockets – the clutch sprocket (sometimes on a jackshaft of a torque converter) and the rear axle sprocket. Typically, the clutch sprocket has 10 – 12 teeth, whereby the clutch sprocket is larger and can sometimes have up to 60 teeth.
This means that the standard gear ratio is 60 to 10 or 60 to 12 (this translates into a 6:1 or a 5:1 gear ratio). In essence, you’ll need to remember the following: the smaller the gear ratio, the higher the top speed.
However, you’ll need to keep in mind that lowering your gear ratio too much can potentially damage some of your go-karts components due to the increased stress that is exerted on them.
Read my comprehensive guide on go-kart gear ratios to find the optimal setting for your Yerf Dog. In this guide, you’ll also find a gear ratio calculator and a top speed table that you can use as a reference.
4. Make Your Yerf Dog Lighter
Weight reduction is another great way to increase the acceleration of your Yerf Dog. The lighter your Yerf Dog is, the faster it will be able to reach its top speed. Keep in mind that this does not increase the maximum speed itself, but it can significantly increase acceleration.
To shed some weight safely, you should consider removing non-essential items and components. You can also replace essential components with lightweight versions.
Here are some things that you can consider removing or replacing:
- Seats – You can replace two-seater seats with single-seater seats, or replace them with lighter seats (the stock seats are relatively heavy and lightweight alternatives are available)
- Storage Tray – Some Yerf Dog go-karts have storage strays at the back of the go-karts. Consider removing this if they are not required.
- Steering Wheel – You can also consider replacing the stock steering wheel with lighter options (however, take note that this may not make too much of a difference)
There are also various components that you should not remove, as they are essential and are required for safety. I don’t recommend that you remove or replace the following:
- Roll cage
5. Remove the Speed Governor
By default, most Yerf Dog go-karts are equipped with an engine that is limited by a speed governor. Removing the speed governor enables you to accelerate beyond the mechanical speed restrictions.
Speed governors, also known as speed limiters, are mechanical components that restrict the amount of throttle that is available. Take note that removing this will require you to have some form of understanding of how go-karts or small engines work.
Read more on how to remove the speed governor of a Predator 212 (this will also work for similar go-kart engines). This will allow you to have full control of the throttle, which will increase the top speed of your Yerf Dog go-kart.
6. Add Isopropyl Alcohol to Your Fuel
Isopropyl alcohol, which is more commonly known as rubbing alcohol, can increase the octane level of your fuel. While this may not be allowed in sanctioned go-kart races, it’s perfectly fine for recreational racing.
Adding rubbing alcohol to your fuel is also known as octane boosting and increases the combustion efficiency of your go-kart engine. Make sure that you go for 91% rubbing alcohol and mix it into your fuel.
- Conservative Mixture (25% Isopropyl Alcohol & 75% Fuel)
- Aggressive Mixture (50% Isopropyl Alcohol & 50% Fuel)
Take note that adding isopropyl alcohol to racing fuel is not allowed in most sanctioned and competitive races. Therefore, you should only use this during non-competitive and non-sanctioned go-kart races.