Memo Gidley's Secrets of Speed for Four Cycle Kart Racing

Part 4: Kart Engine Installation and Setup

Words: Jeff Grist and Memo Gidley // Photos: Sean Buur

Engine Setup

Now, let’s move to the engine side of the kart. In this section we will look at the throttle adjustment, carburetor installation, exhaust pipe mounting and chain tension.

Let’s start with the carburetor. The clamping boots on the carburetor manifold should be snug but not overly tight. Over tightening the clamp will bend the clamp and excessively squeeze the rubber boot, which may result in an air leak. Make sure you have the style of clamp that has rounded edges so it does not cut into the rubber boot. The fuel lines need to be tye wrapped on the carburetor nipples to make sure no fuel or air leaks occur. Some carburetors bolt on directly like the Honda GX200, so be sure the nuts are snug on the studs.

Wide open Slide and Butterfly style Carbs.

Next, we need to check to see that the throttle slide closes completely.

First, remove the air filter. For engines such as the F200, which use a butterfly style carburetor, it is important to make sure that the butterfly shuts completely when you release the throttle pedal. To check the butterfly operation, push the throttle pedal until it contacts the stop. Now, look into the carburetor and make sure that the butterfly is fully open. It is possible on this style of carburetor to open the butterfly past center which will slow the motor down. Only go until the butterfly is laying flat when looking straight into the carburetor. Now release the throttle to be sure the butterfly closes completely.

For engines like the Animal and the World Formula, which use a slide style carburetor, push down on the gas pedal to make sure the slide rises all the way out of the carburetor bore. Adjust as necessary using the pedal stop or the adjustment screw at the top of the carburetor. Put the air filter back on and tighten the clamp.

Step back and make sure that everything looks right with the routing of fuel lines. The flow needs to be natural and smooth, with no kinks or sharp turns.

Keep an eye on sharp edges that could cut into a line. If you are concerned with chaffing, wrap the hose in some type of anti-chaffing material. Remember that on a kart everything moves and vibrates.

Next, be sure to check the header pipe. The flange needs to be tight and you should be sure to use lock washers to ensure they stay tight. Your header will need a support of some kind. You can use a short support mounted to the engine as used on the Raptor or Honda GX200 or a frame-mounted support as used on the Animal, World Formula and F200 pipes. In some cases, like the World Formula, the support bracket uses a self-tapping bolt to secure it in the pre-drilled hole in the engine block. A loose or unsupported header is more likely to break and result in a black flag or DQ. Also, you may want to wrap your pipe in header wrap, an asbestos material designed to protect you and your suit from being burned on the hot pipe. In some race series they require the silencer to be safety wired to the bracket.

Complete exhaust system requires mounting brackets.

The final step is to set the chain tension. Loosen the engine adjustment bolt and the engine mount bolts. This is a good time to check the bolts and the engine mount for cracks or wear. Push the engine forward until the chain has slightly more play than you might want. Now snug up the bottom motor mount bolts. This will help to make sure that the motor is resting on the frame and that you will have a little tension on the adjuster when you are ready to set the chain slack. Bring the engine adjustment bolt forward to touch the mount. As soon as it hits the mount, you should start to feel a little bit of extra tension. Now, slowly turn the adjuster until the chain has approximately 3/8” (12mm) of slack. When the desired free play is reached, tighten the bottom motor mount bolts and the chain adjuster lock nut.

Be sure the engine mount is tight.

Now slowly rotate the axle to make sure that you have the same slack in the chain throughout the entire range. A problem you might find when adjusting your chain is getting a tight spot. A sprocket that is not quite centered on the hub usually causes tight spots in the chain. Most sprocket boltholes are slightly larger than the bolt. If you find a tight spot, back off the tension on the sprocket bolts so that they are just snug. Rotate the sprocket until you feel the tight spot. With a rubber mallet, lightly tap on the back of the sprocket.

This will shift the sprocket slightly forward and give you a little slack. Rotate the sprocket and again check for uniform tension. If you went too far or not far enough, try again. When you get the proper tension, tighten the bolts. Make sure the chain guard is in place. This is a tech item and is good protection for you if the chain breaks. Also, the chain guard will keep your kart free of flying grease.

Getting it Started

Now that you have completed your routine check, you are almost ready to fire up your kart. Before you fire up the engine, you need to add fluids to your kart. Make sure you follow all the manufacturer’s recommended type fluids and specified amounts. Check with your local dealer or engine builder if you are not sure what fluids your kart requires. With four-cycle engines there is no need to mix oil and gas. The crankcase of the engine will take any 30-weight oil. Some engine builders will recommend very thin oils. In most cases, your four-cycle engine will run with regular grade pump gas.

It is a good idea to fill the fuel system before you try to start the engine.

After putting fuel in the tank, take the fuel line off the carburetor and aim it into the gas can. Blow into the gas tank vent line until fuel flows through the fuel line and into your gas jug. Now that the fuel line is full of fuel, attach the fuel line back onto the carburetor. Filling the line with fuel will keep you from having to turn the motor over excessively to start it. Make sure you put a small tye wrap over the fuel line to keep it secure on the carburetor nipple.

Always support the exhaust system to avoid any unnecessary problems.

Have your friend stand at the front of the kart applying approximately an eighth of throttle. Put the starter gun into the nut or pull the starter cord and turn the engine over. Once the engine starts, run at a low RPM until the engine warms up. If the idle is set properly, the engine should idle nicely at about 1,500 to 1,600 RPM. If not, adjust the carburetor idle by adjusting the cable or the idle screw.

Base Line

To make sure the handling of your kart will be accurate and correct, you need to do a basic chassis set-up before you go out onto the track. This will include setting the ride height, front and rear track widths and tire pressures.

It is recommended that you ask your kart manufacturer for a basic set-up starting point based on your height, weight and skill level. If this information is not readily available, here are some quick generic settings to get you started. Most karts have adjustable front and rear ride heights. For the front, start with the middle setting in order to give you room for adjustment. If the rear of the kart has only two settings, high and low, choose the higher setting to begin with. The front track width should also be set in the middle of the available range, so split the spacers equally.

Rear track width should be set depending on the compound of tire on your kart. A good starting point for hard compound tires is approximately 52”, while a softer should be close to 55”. This is the measurement from the outside of the left rear tire to the outside of the right rear tire. Make sure the front and rear hub bolts are tight.

Next, you need to get a basic tire pressure. Each tire compound has a different optimum operating pressure. This information can be very difficult to find or not available at all. Generally speaking, the front tires should be two to three psi less than the rear tires. This is because the front tires have a much shorter and stiffer sidewall and don’t need that extra air support like the rear tires.

Normally, the harder the tire compound, the more pressure you will want, to ensure maximum grip.

I would recommend 10 psi in the front and 13 psi in the rear for a soft compound tire, a 12/15 psi front/rear setting for medium compound tires and an 18/23 psi setting for hard compound tires. These are COLD tire pressure recommendations. This means that your HOT tire pressures should be two to three psi higher after your run.