Best Motor For Go-Kart
Article by Mark Trotta
If you're looking for a motor to power your next kart project, you have over 60 years of small engine technology to choose from! This article covers the different types of single-cylinder gas engines best suited for yard karts and fun karts.
Traditionally, go karts were powered by modified lawn-mower engines, usually a 5-horsepower (or less) 4-stroke engine. Briggs & Stratton and Tecumseh were the most common brands, although there were others such as Lauson, Clinton, and others.
Horizontal vs Vertical Engine
Although a vertical-shaft engine can be adapted, the best choice for a go kart is a horizontal-shaft (side-shaft) engine. These are commonly found on gas-powered lawn equipment such as garden tillers and two-wheel lawn mowers.
Can You Convert A Vertical Shaft Engine To Horizontal?
A vertical-shaft engine will not work properly on it's side. It will start and run, but the engine internals will not be lubricated properly and will quickly lead to seizure. This is because most small engines are splash lubricated by the engine oil.
2-Stroke vs 4-Stroke Kart Engine
When karting first began,two-cycle engines were very popular. They were lighter in weight and capable of higher RPM's. Today, two-stroke motors are usually seen only on race karts, with brands such as Rotax, Yamaha, KTM, and Mcculloch. The power curves on these engines are best suited for top end (racing) and run up to 10,000 rpm or more.
Pound for pound, a two-stroke with the same displacement as a four-stroke will make more power. Keep in mind that a two-stroke engine may be good for propelling a 140-150 pound person (plus a 50-pound kart), but will have a hard time pushing a 180-200 pound person (plus a 50-pound kart).
Some people like the sound of a high revving two-stroke, some people don't.
How Much Horsepower Do I Need For A Go Kart?
Take into consideration who will be driving the kart and where the kart will be driven. Safety needs to be at the top of the list, especially if younger people will be driving.
3 horsepower - This type of engine is the best fit for younger (smaller and lighter) drivers.
5 horsepower - Any 5-hp engine with a few modifications should be more than enough power for a yard kart. The most common is the Briggs & Stratton flathead engine.
6.5 horsepower (and above) - These will be more contemporary engines, such as Honda, and the many Honda clones.
NOTE: Wisconsin-Robin are flathead-type engines are not to be confused with today's Japanese-made Subaru Robin.
Honda GX Series
The Honda GX series of small engines are very well built and have proven to be long lasting. Two of the most common examples are the Honda GX160 and GX200 series.
Honda Clone Engines
The low cost of Honda clone engines makes them very popular. They were designed to share parts with the Honda GX series engines.
One of the most popular Clone engines is the Chinese-made Predator 212cc. These motors have put a good number of old go-karts back on the road. In stock trim, it produces 6.5 horsepower, and can be easily modified.
Old School Go Kart Motor
The 'look' of the Honda and clone motors is quite different than old-school flatheads. One main difference is that the cylinder is more horizontal.
Most factory go karts from the 1960's and 1970's were fitted with either a Briggs & Stratton or Tecumseh flathead engine. Both brands have the same mounting bolt pattern, so swapping one for the other is easy.
Many flathead small engines from the 1960's-1980's are still around, and they are a great choice for a vintage kart build.
5-Horsepower Briggs & Stratton Motor
The five-horsepower Briggs flathead is one of the most popular small engines of all time - so popular that there are racing classes based on it. These old motors are durable, reliable and easy to repair. There are still plenty of parts suppliers for these 50+ year old engines.
5-Horsepower Tecumseh Motor
Tecumseh and Briggs flathead motors are not that much different from each other internally, although one difference between the two is the connecting rods. The Tecumseh rod bolts have knurled heads, which are designed to mate with the soft aluminum rod material. Exercise caution when tightening these bolts! Service manuals state only nine foot-pounds is required.
An important engine spec to keep in mind when selecting a suitable kart engine is the output shaft size. The most common size is 3/4" diameter with about 2" of stick-out length. A longer shaft will work (you can always cut it), but a shorter one limits your options to engine placement.
A crank diameter can be increased with a shaft adapter bushing, also known as a crankshaft sleeve. These will allow you to keep or swap components such as a torque converter pulley.
A small 5-horsepower or less engine will have either a diaphragm-type or a float bowl type carburetor. Both have advantages and disadvantages.
Detached Gas Tank
This flathead Tecumseh engine has a non-original, detached gas-tank, which sits above the motor. Being gravity-fed means a float-style carb must be used.
An external gas tank is sometimes awkward, but it does give you the option of mounting it anywhere you want (within reason).
Centrifugal Clutch vs Torque Converter
A centrifugal-type clutch is found on most old-school go-karts, and they're the cheapest and easiest way to get power to the rear wheel. Their shortcoming is they do not like "stop and go" acceleration. If you drive it this way, the clutch will have a short life, so it's better to run pedal down or not at all.
An alternative to a centrifugal clutch is a torque converter. This will allow you to run the gas pedal on and off without risking burning up the clutch.
Read: Best Torque Converter For Go Kart
NOTE: Before ordering a centrifugal clutch or torque converter, measure the width of your output shaft. Most 5-hp motors have a 3/4" (.750") shaft, but older and smaller horsepower engines may have a 5/8" (.625") shaft.