Maybe you don't have a go kart. Why not build one? Here are some other instructables on how to build yourself your first kart:
Make your own Go-Kart.
Design and Make Your Own Go-Kart
It doesn't matter how many wheels it has, it doesn't have to be a 3 wheel like mine, it could have 4 wheels or even 2 (mini bike), the same basic principles apply.
Stay tuned because the engine section applies to any small engine, like what is found on lawn mowers, pressure washers, generators, etc.
Step 1: Brakes
Arguably the most important feature when using your kart is the ability to stop. Before you forget about it, check the break hardware first.
Pull the brake lever(s) or push the brake pedal (left pedal) and try moving the kart. You shouldn't be able to move the kart and have the wheels with brakes on them turn. Also check for "slop" in the brakes. The brake should engage when the lever or pedal is just moved a little bit. If you have to pull the lever almost all the way to the handlebar or push the pedal almost all the way down, your brakes need adjustment. Hydraulic brakes are self adjusting. You can tell if you have hydraulic brakes if there is a reservoir for adding brake fluid.
To adjust a brake lever, unscrew the cable retainer from the lever a little bit and try the brake again. The retainer is the green thing in the picture below. You should need pliers when you first start unscrewing the retainer. You might have to unscrew the lock nut in order to get it to turn freely. When it's adjusted right, the brake should fully engage by only pulling the lever a little bit. If the retainer unscrews all the way, this is a sign that you either need new brakes or they need to be adjusted down at the caliper/band/drum. If you don't know what you're doing down there, take it to someone who does. The health of you and/or your children is more important than a couple bucks saved by doing an adjustment yourself.
To adjust a brake pedal on the 4 wheel karts, follow the rod linkage from the petal to where it ends. There should be some threads and a nut there. It should be apparent now how to do the adjustment. If it isn't, take it to someone who knows what they're doing.
You'll also want to check the amount of brake material on the pad/band/shoe(s) that it isn't below the wear indicator or isn't excessively worn. Again, I highly recommend taking it to someone unless you've done brakes before and are confident with your own work.
Step 2: Tires
The next thing you'll want to check is the tires. Make sure there's plenty of tread and check the pressure with a low pressure tire gauge. The correct pressure is written on the sidewall of the tire. The front and back tires may be different and require different pressures.
Roll the kart around and make sure the spindles/axles aren't bent. Lift up the ends of the kart with blocks of wood or something and spin each wheel. The rear wheels will turn together if you have a live axle setup. Check for roughness, looseness, and/or rubbing against the frame. The wheels should spin easily and not make much of a sound. The bearings will go bad especially in a rough and dirty environment.
Step 3: Steering
Now that you're all tired out, turn the handlebars or steering wheel to check for any looseness or roughness. If present, have the the steering overhauled.
Step 4: Drivetrain
This could practically be its own instructable. Basically check for loose chains, noise, roughness, and bent stuff. Then clean and lube the chain and centrifugal clutch as below. If you want to get deeper into it, read on. Otherwise take it to someone who knows what they're doing. The health of you and/or your children is more important than a couple bucks saved by doing an adjustment yourself. Some of this stuff should really be done every time you ride.
On almost every kart, with a couple exceptions (like the Manco Fox Helix), there will be at least one chain. Before you do anything else with it, you may as well check the tension and look it over, because if it's worn out, there is no point in cleaning it.
The first thing you want to look for is bent or misaligned sprockets and wear. One of the sprockets is going to be part of the centrifugal clutch if your kart is so equipped. There shouldn't be any back and forth movement when you spin the axle. If there is then the chain, sprockets, and probably the axle need replacement. Look at the sprocket teeth very carefully. Each tooth should be the same on both sides - symmetrical. If it appears that the teeth are "leaning" then your sprockets are worn out. Have both chain and sprockets replaced. Replacing only one or the other is just going to wear out the new part very quickly.
To check the sprocket alignment, get out your straight edge and put it between the 2 sprockets along their sides so that it's not resting on the chain. Now look at where the straight edge is touching the larger sprocket. The straight edge and big sprocket should touch all along the length of the sprocket, except at the edge of the sprocket where the teeth are. Make sure it's touching the side of the little sprocket where it's thin and not just the teeth when you're checking this, not the central hub part or retaining collar where it's fatter. If you can see any gap between the straight edge and the big sprocket then you have alignment problems. Have the sprockets aligned. You could also align it yourself by guiding off the big sprocket with the straightedge and moving the little sprocket, checking with the straight edge until they're aligned.
When you pull up and down on the chain, it shouldn't move any more than 1/2", maybe 3/4" on longer runs. If you're a metric nut then let's say around 1cm. If it doesn't move at all and you can strum it like a guitar string, then it's too tight and has to be loosened up. If there is a tensioner sprocket, have it tightened or loosened . If not and it's too lose, replace the chain and maybe the sprockes. If too tight, try adding links or half links and check the tension again. Spin the axle. The chain should make no noise or very little noise.
The worst enemy of chains is sand followed closely by metal shavings. You should be able to run your fingers up and down the chain and get only clear lube (or colored lube if your lube is colored) on them. If the chain is dirty or sandy, take a couple cans of WD-40 and a toothbrush and scrub that thing real good. Then apply some fresh lube. Some good chain lubes recommended by karters are Silkolene, MFR, and PJ1. These are good for anything with a chain.
You should really take off the chain at this point and check for "kinkiness". All of the links should move back and forth effortlessly. The rollers should spin freely and easily.
If your chain and sprockets are rusty, then they need to be lubed more often. Sometimes you can bring back a seized up chain by throwing it in an old coffee can with some 10W30 oil and heating it. ATF might work well because it is high in detergents. I suppose you could also try soaking it in PB Parts Buster, Liquid Wrench, or antifreeze (which has corrosion inhibitors).
You should put a little 3 in 1 oil on the bronze bushing (see the picture). Don't go overboard with it or put oil anywhere else because if it gets on the shoes inside the clutch it could fail. You might have a grease zerk on the end of the crank. If you do, skip the oil and give it like a half pump with a grease gun.
COMET TORQUE CONVERTERS
What is a torque converter or C.V.T (continuously variable transmission)? It's just a couple special pullies and a belt. If your kart has a Comet torque converter there is some additional light maintenance to do on these.
Check for rust on the parts the touch the belt. Rust here could cause premature belt failure and require one or both pulleys to be replaced. If the rust is light it could just wear off on its own as the kart is used or you could sand it off.
The pulley on the engine crankshaft (driver pulley) has weights inside that periodically need to be cleaned and lubed. You can skip this, but I recommend doing it or having someone else do it for you. You have to take the cover off to get at these. Use an old t-shirt wound around the pulley or a strap wrench to get a grip and remove the bolt in the center. Take the cover off (it might fall off all by itself) and clean everything you see with brake cleaner really well. Also clean the underside of the cover. When it's clean and dry, it's time to lube. Lube only the weights and surrounding area. Comet recommends lubing with their special lube, but you could use graphite in a pinch. DON'T USE GREASE OR OIL! These attract dirt and belt dust. Go ahead and take the whole thing off the crank if you're so inclined and clean everything with brake cleaner. Don't lube anything else, especially anything touching the belt. You can also take apart and clean the driven pulley, but don't lube this either.
Check belt for fraying and excessive wear. Replace accordingly.
Step 5: Engine and You're Done
Finally on to the engine. I mention this last because the engine is what gets you moving and you don't want to be moving if something as important as the brakes or tires is out of whack.
The gas tank and carburetor should be empty. (you did drain out the gas last fall, didn't you?)
Check the air filter. There's usually a wing nut or two and a cover to remove. Paper elements should be white or light gray. Dark gray or black means it needs replacement. Paper elements are not serviceable. If it's dirty, throw it out and put in a new one.
Foam elements on the other hand can be washed with soap and dish detergent and squeezed dry. Do not wring out a foam element, just squeeze the water out. Then add a couple drops of oil and squeeze it again to distribute.
If you've been running in mud or heavy brush, you should probably remove the shroud and blow out the flywheel and cooling fins with compressed air. If you don't have an air compressor, sometimes you can get away with one of those little whisk brooms. Briggs & Stratton and Tecumseh shrouds usually have 4 bolts. Find all 4 to remove the shroud and reveal your prize!
Check the oil, which is something you should do every time you ride. The oil should be changed every 25 hours of use.
To change the oil, put something underneath the engine to catch the oil and remove the drain plug.
After it's all drained out, tilt it to get that extra little bit out if you can.
Replace the drain plug.
Remove the dipstick and, using the appropriate size funnel, start filling with SAE30 engine oil. NOT 10W30, NOT anthingWanything, SAE30. (some of the Honda engines call for 5W30, read your owner's manual)
Periodically stop and put the dipstick back in to check the level. Either that or pre measure the prescribed amount as specified in the owner's manual (you did read that old thing, didn't you?)
Take out the spark plug and check it for fouling and wear, gap it to .030" with your feeler gauge or replace with a new one.
Now put in the FRESH STANDARD GRADE gas YOU JUST GOT, not the stale old gas from last season, not the gas you siphoned from the old truck rusting in your driveway, not the high octane superultraplus++, no octane boosters, not an old gas EVEN IF you put stabilizer in it. Just put in FRESH, plain old STANDARD GRADE GAS.
A couple pulls and you're off. Otherwise there is something wrong with your engine and you need work done. See some other instructable if you want to plunge yourself into that mess. See you on the trails.