How to bump start a Direct Drive Kart

This is ONE man’s view on the best way to SUCCESSFULLY push start a 2-stroke, direct drive kart: it’s not the ONLY way.

I’ve written the article as though all the participants are male and right handed. This is obviously untrue but it makes the writing simpler if I write for the majority. Please do not take offence to this style; none is meant! Two of my quickest ever teammates were female and one was left-handed!

PREPARATION

The first thing to do is to check that everything is working BEFORE you get to the track, preferably, on a stand in your garage.

SAFETY:

NEVER, NEVER, NEVER try starting the kart by putting a rope/strap round the tyre and pulling. It MAY work but it MAY also KILL YOU. The end of the rope can get caught in the chain/axle or whatever and it will ‘reel you in’ and cut you to ribbons. If you’re lucky, you’ll just lose a hand or an arm, if you’re not..……………………..

SPARK PLUG

Remove the plug and reconnect it to the plug lead. Lay the plug on TOP of the engine (preferably, with the sparking end AWAY from the plug hole as it can ignite any fuel in there; it may be fun but it’s not too clever!). You MUST make sure that the metal of the spark plug makes good contact with the main metal of engine whenever you spin the wheels or you can damage the ignition system. Now spin the rear wheels and you should see a healthy (fat) spark. If it looks feeble, buy a new plug.

Check the spark plug is clean and not ‘wet’ (oily or dripping fuel). The ideal colour is from ‘brand new’ to mid-brown. Black is OK but it’s better to get a wire brush and clean it up. If it’s caked in rubbish of any colour (a bit like the ‘fur’ in the kettle), clean it or chuck it!

If you don’t get a ‘fat’ spark even with a new plug, your ignition system has a problem and it’s NEVER going to run without skilled help.

Remember what the clean, dry plug looks like as this comes into play when we get to the ‘starting’ part of this article.

FUEL SYSTEM

Your carburettor has an inbuilt fuel pump. The action of turning the motor causes the pressure to rise and fall inside the crankcase. There is a connection between your crankcase and the carburettor (a tube or a drill hole in the rear of the carburettor) that uses those changes in pressure to pump the fuel. Many things can fail in a carburettor but they can all be fixed. The simplest test is to check that the fuel pump is pumping! Remove

the spark plug, reconnect the plug lead and make sure the plug makes good contact with the cylinder head. Now, place the flat of your hand over the air intake (at home, it’s easier with the air box removed), open the throttle FULLY and spin the wheels quite briskly. You should now see fuel moving up the pipe to the carburettor. What’s happening is that an engine is really an ‘air-pump’; when you turn it, air goes in through the carburettor and out the exhaust. By blocking the air intake, you are preventing the air getting in and the pressure inside the carburettor drops and that ‘sucks’ the fuel in. You MUST open the throttle or this ‘choking’ trick DOES NOTHING AT ALL (many people don’t know that!)! This is because the main fuel inlet is on the ‘other side’ of the ‘throttle’. So, if it’s not open, it DOESN’T ‘suck’ the fuel in!

If fuel doesn’t come up, you need to check that all the fuel lines from the tank to the carburettor are connected properly. If the pipe/s are too stiff, they can let air in and stop the fuel from moving. Buy good quality fuel lines. Un-leaded fuel is really aggressive stuff and pipes harden very quickly if you leave it in the pipes after driving the kart. It’s a good idea to empty the fuel pipe as much as possible after each race/practice day. The pipe will last much longer this way.

Once you’ve got the fuel up to the carburettor, you can check if the fuel pump is working. Take your hand off the air intake and spin the wheels again. You should be able to see the fuel ‘moving’ very slightly in the fuel pipe. This is the action of the pump on the fuel, not the ‘choking’ reaction. It’s not a problem if there are small bubbles (up to about 1cm) in the fuel line as this is quite normal. In some ways, they are quite an advantage as you can see what’s going on with the fuel. You may need to use the ‘choking’ method BEFORE you can test the pump. To work properly, the pump should have fuel all the way up to (or very near to) the carburettor. If you have not ‘choked’ the fuel all the way to the carburettor, the fairly feeble pumping may not be strong enough to overcome the air inside the fuel pipe.

This is a LONG explanation; but there are many other things that can still be ‘wrong’ even if everything checks out perfectly up to this point. But, if you have a FAT spark and fuel up to the carburettor, you are 90% of the way there.

Starting the kart at the track

Starting is all about getting the kart moving forward and KEEPING it moving forward until it’s able to accelerate way on it’s own.

To make life easier, make sure everything is ready BEFORE you start pushing. You will have checked the spark is good and ‘fat’ and that the fuel is getting to the carburettor BEFORE getting to the track. Now make life easier by getting the fuel up to the carburettor BEFORE you start pushing. You can do this by ‘rocking’ the rear wheels back and forth while ‘choking’ (as discussed before). DO NOT MAKE THE ENGINE TURN OVER BY HAND; it may well START and trap your hands! You can do this while sitting in the seat or with the kart on the stand. Once the fuel is up and ready, we’re nearly ready to push the kart.

There are two basic methods:

1) Driver Seated

2) Driver Running!

DRIVER SEATED

Lucky (or rich drivers) have two pushers, but one is plenty, if they are reasonably fit and sensible and he really does not need to be an ‘Arnold Schwarzeneggar’! There’s no way round it, the angle and the task is not good for the pusher’s back; those with troubled backs or hernias should NOT apply! It’s also a good idea for the pusher to do a few backstretches before he goes for each new attempt.

Firstly, get the driver to lean right OVER the steering wheel. The driver should attempt to grab the FRONT bumper! This moves the weight forward and makes the pusher’s job MUCH easier. You can improve on this if the driver sits on the front EDGE of the seat as well as leaning over. It makes the kart ‘feel’ about HALF the weight to the pushers and this is VERY worthwhile

LIFTING

The driver should also try this bit so he can see that the pushers have to do. It’s all about getting your bum as LOW as possible.

The WRONG way

With a driver seated, try placing your feet so that both of your legs just touching the rear bumper and both hands are on the bumper and then lift the kart. You’ll find that you can only move very slowly forward in small steps as you keep banging your ankles on the bumper. You’ll also notice that the pusher’s centre of gravity is almost over the rear bumper. This is OBVIOUSLY the wrong way to do it! However, this is exactly what all beginners do; hence their problems starting the kart!

The RIGHT WAY

With a driver seated, stand with your RIGHT foot under the rear bumper and your LEFT foot about 3/4s of a metre back. Place your right hand on the bumper (to lift it) and your LEFT hand on the back of the seat, just to steady yourself. You’ll only be lifting the kart with your RIGHT hand. You’ll now notice that your bum is MUCH lower than before and that you don’t bang your ankles on the bumper. Ideally, the pushers want to look as HIGH into the sky as possible by ‘craning’ their necks back as far as they can go! The pushers **** MUST NOT **** look down at the kart or the track! You’ll notice that, the higher the pusher looks:

1) the lower their bums are

2) the further back they will have moved their left foot .

3) the further back their centre of gravity has moved

This will allow them NOT to fall over when they have started the kart; more about this later. KEEP THEM LOOKING UP!

Oddly enough, when you get used to this, you’ll find that you lean DOWN with the LEFT hand on the back of the seat while you are LIFTING the kart with your RIGHT hand. This lets the pusher’s Centre of Gravity even further back and leaning forward on the back of the seat (with the left hand) is the start of the PUSHING action

Lift and PUSH

An engine does not want to turn over as the compression is holding the piston ‘back’. We lift the kart so we can get some forward momentum that will be enough to overcome the compression resistance. We don’t have to move very far forward before we hit the ground as a walking pace is enough to do the job of overcoming the initial resistance! Similarly, we don’t need to lift it very high, just enough to get the kart moving without the friction of the rear wheels. About 5 cm is the MAXIMUM you need to lift. Any more than that and the nose cone will be rubbing on the ground, which makes it harder.

The first part of the pusher’s job is to lift the kart, move forward about 1 metre and then PUSH it down and forward onto the track. They should be prepared to CONTINUE pushing for a good few metres; their job has not finished…….. YET!

Now for the driver! Engines need a mixture of Fuel and Air at a specific ratio to run. The colder the air (and the engine) the MORE fuel is needed in that ratio. Stone cold engines on a cold day need MUCH more fuel in the mixture than hot engines on a hot day. Older cars were fitted with a Choke Knob or Lever to adjust this ratio, nowadays, that ‘choke’ is automatic. Karts don’t have automatic chokes (most don’t have ANY sort of choke!) so you need to be your OWN choke. It’s as the name implies, you are trying to STRANGLE (choke!) the engine by cutting off its air supply. You do this by placing the FLAT of your hand over the air intake. What happens is that the air can’t get in so any ‘suction’ inside the carburettor pulls in extra fuel instead. Remember to open the throttle FULLY or choking is a complete waste of time!

Just before the pushers start their work you should have your hand OVER the air intake but NOT actually closing the intake off just yet. I just rest my fingers on the casing/airbox so that I can choke if I need to without frantically searching for the opening. Once you’re helmeted and seated, it can be hard to find the air intake in a hurry, so: Be Prepared!.

As the kart hits the ground, slide back into a proper seating position. You will have previously warned the pushers to move their hand AWAY from the back of the seat once the kart has hit the ground or your will TRAP them as you sit back! If they get trapped, you will drag them along the pit lane, not too much fun that! Get them to transfer their hands (smoothly) to your shoulders and KEEP pushing and KEEP LOOKING UP!!!!!!! Make their job easier by not leaning QUITE ALL the way back; if they’ve forgotten about getting trapped, you have allowed them some freedom to escape.

The driver’s work starts here! It’s highly possible that you won’t need any choke and that choking at all will stall the engine. It’s also highly possible that it will need a LOT of choking. You will gain experience and be able to judge this for you self with practice. However, as a beginner it’s worth getting into a routine based on the distance that you have been pushed!

1) 0 to 5 metres

Don’t Choke. Just start increasing the throttle setting, (if it fires, go to point 4)

2) 6 to 30 metres

Go to full choke (hand firmly over the intake) and FULL THROTTLE, if it fires, lift your hand away from the intake but keep it hovering over the intake just in case it stalls again. (If it fires, go to point 4)

3) 31 metres onward

If your pusher is still going, take your hand away from the inlet (but ‘hover’) and give FULL THROTTLE. If you have prepared as discussed and you have been choking for 30 metres, it’s more than likely that the engine is now flooded rather than being starved of fuel. Full throttle will allow the engine to dry out a little and it may fire IF your pusher can keep going! (If it fires go to point 4).

4) The engine fires

Once it fires, lift your hand a SHORT distance away from the air intake so as to let in unrestricted air but still with your hand ‘hovering’, to be ready to apply full choke if the engine tries to stall as it may WELL do! If you’ve put your hand back on the steering, wheel it’s much more of a game to re-find the air intake before it stalls.

Obviously, when it starts to fire, you will ‘un-choke’ (if you have been) and you should also REDUCE the throttle position. It is WRONG to accelerate away at FULL throttle within the pits! Out on the track, it’s OK if it’s safe (no pushers ahead of you) but that happens all too rarely! It’s also a very clear sign of lack of mechanical sympathy. Anyone who accelerates an engine (cold OR hot) to full throttle and full revs immediately after starting shows they do not understand ANYTHING about engines! If you see people do this, simply think “IMBECILE!”. The list of disasters that can go wrong by abusing your engine in this way is longer than this article!

Remember! Be Prepared! The engine may well try to stall, just put your hand back over the intake and go to full throttle again.

This is why the pushers MUST keep pushing until they can’t stay with you! Many engines will stall even after they have started and a ‘dead’ kart in the middle of the starting straight is NOT much fun for those trying to start their karts behind you. You will find that many IMBECILES behind you are looking back at their carburettor as they start their engines and they will drive straight INTO your stationary kart! (I can never imagine what they hope to see back there! Drivers: keep looking FORWARD!) If your pushers are still behind you, the following karts crush your pusher’s ankles against your rear bumper; NICE! Tell your pushers they MUST, MUST, MUST KEEP RUNNING once you have started and to CHECK behind them as they RUN off the side of the track/pit lane! All this is just common sense but you would not BELIEVE how RARE that is on a kart track!

As the kart starts, the point of your pushers having a ‘low bum’ and their Centre of Gravity as far back as possible comes into play. If they are looking down, with both feet together, they will FALL OVER when the kart starts! If they are looking at the sky, they will be able to stand up and keep running!! The choice is theirs!

If there are only two of you, your pusher MAY not have enough strength to lift and push you. It’s not that hard once you’ve practiced but may well be completely beyond a beginner. There are many alternatives:-

Easy Start Wheels

Kart shops sell all sorts of easy starting tools from long handles levers with wheels to things that look like tall skinny roller skates. You use these to hold the kart off the ground while the pusher gets up to speed and then ‘drops’ the kart onto the track and carries on pushing. Of the two, I prefer the short roller skate type but, as a first choice, I’d go for the old-fashioned un-assisted lift and push even though I’m 50 years old (and fat)!

You can buy a device that bolts a single ‘additional wheel on a lever’ onto the underside of the kart. You lock it into position, push the kart and then release the lock, which collapses the wheel out of the way. These are great but they add weight. They also make one more thing that can go wrong on the kart! However, they do allow the driver to ‘trundle’ the kart back to the pits if it fails on the circuit.

Driver RUNNING

This is the MOST ‘professional’ way! Assuming there are two of you, the pusher does exactly as before but the driver stands on the RIGHT hand side of the kart with his LEFT hand on the rear of the seat and the RIGHT hand on the top of the wheel. The pusher does exactly the same as with the driver seated but he now has almost no weight to lift. Once the kart is ‘airborne’ and moving forwards, the pusher and the driver MUST push down to stop the wheels from skidding as it hits the ground. As before, the pusher KEEPS PUSHING!

The driver runs with the kart for about 3 metres and then swings himself into position and this should be practiced first ON YOUR OWN with the kart stationary. The driver is trying to lift himself into the kart by supporting his weight on the top of the wheel and the back of the seat. The driver then swings himself into the kart so that his RIGHT foot lands just behind the throttle peddle and the LEFT foot lands in the centre of the seat AT THE SAME MOMENT! Bring the LEFT hand to the wheel and get your LEFT foot behind the brake pedal while sitting down. (The kart WILL start whether you have your foot near the brake pedal or not; it’s up to you how important this is to you. Think of the implications if the throttle is stuck wide open and you don’t have your foot near the brake!). Your RIGHT hand now goes to the ‘Hovering Choke’ position.

It all sounds REALLY complicated but it isn’t! Practice with a stationary kart until you can easily swing yourself in. Then try with it with your pusher but with the spark plug out (but ‘strapped’ to the top of the engine). This will make sure it won’t start and there will be little or no rolling resistance. You can obviously do this on your driveway or down the pavement if the plug is out! You can even do this on your own (with the plug out) and you will be shocked how simple it all is! The first few times can be embarrassing as you accidentally turn the steering wheel and run over your foot but you’ll get the hang of it very quickly.

As I said, this is the professional method. If you master this technique, you don’t NEED a pusher because you can do it all on your own! It’s not so important IN the pits but it WILL get you going again out on the track once you have spun off! You’ll find you don’t need to LIFT the kart right off the ground, just slightly release the weight (by pulling the seat

upward) and you can simply SLIDE it before you push it DOWN to turn the motor over. Once it’s moving along quickly, you can jump in but you must get to the throttle pedal quickly to get you going. The engine will probably be warm and should start without choke!

What to do if it doesn’t start after a ‘good’ push

There are usually two possible reasons (assuming everything else checked out properly, earlier). Either, you have choked too little or you have chokes too MUCH!

If you can see fuel dripping out of the carburettor or air box, obviously, you’ve choked too much! However, it may not be visible. You can get over this by pushing it again with NO CHOKING BUT FULL THROTTLE! It may well start as the engine is, in effect, fully choked already! However, it may be too flooded (over choked) to start.

You can check if it’s flooded or not by removing the spark plug and looking at it. If it’s wet and/or oily, you’ve choked too much. If it’s dry, …. well do I need to tell you? Please do this checking IN YOUR PIT BAY! The reason is simply SAFETY. If you are on the side of the track with 1 or two pushers fiddling with the spark plugs, there is a GOOD chance someone will crash into you!

A dry plug tells you try again but choke and push for longer! How far should you push? Until your pushers drop in a small heap! I have done well over 100 metres as a solo pusher and managed to get it going in the end!

A wet plug means that you need to dry it and get rid of the excess fuel in the engine. Firstly, put the kart back on the stand and clean and dry the plug. A spray can of ‘EASY START’ (yellow and black spray can of almost pure ether; any car spares shop sells it) does the job VERY well. This washes the oil out of the plug. A small wire brush will clean up the plug nicely. Plugs DO fail and it’s well worth buying the CORRECT plug for the weather conditions; ask your kart shop for the right plug for the conditions. A wrong plug on the wrong day can melt the piston so GET IT RIGHT!

If the plug was VERY wet and oily, the inside of the engine will also be very wet and it’s a good idea to dry it out as much as possible. You can do this by rapidly spinning the rear wheels with the plug out (but connected!) and the throttle fully open. If it’s very wet, you will see plumes of oil/petrol spray ejected from the plug hole; GOOD! Do use some sense about smoking near this little lot!

Now put the plug back and start again.

As a last resort before abandoning the project, try to borrow a spark plug that’s still HOT from being run in another kart. That little bit of heat can make the difference. Once it’s running (one or two laps), come back to the pits and change back to your own plug! Be careful when handling HOT plugs, they will burn if you’re not careful

Finally, spend 10 minutes looking around the pits to find a team who ACTUALLY knows what they are doing so you can ask for advice. It’s quite easy to tell if they are worth asking. If the kit is new and expensive, they are either:-

1) serious karters who can’t spare you the time of day

2) over-rich twits who don’t know what they are doing but have spent a FORTUNE on smart kit.

Scruffy, tatty karters do not understand their OWN kart let alone yours! You want to look for someone with tidy but older equipment, a decent toolbox and a ‘Dad’ who isn’t shouting his mouth off! They will be a ‘team’ that would LOVE better equipment but can’t afford it and will have been through all the problems that you have and will PROBABLY be willing to help.

That’s about it! Other problems may still prevent it starting but that will indicate a mechanical failure somewhere and that is probably going to need professional help.

Summary

Mechanic

Check Fuel and Spark before going to the track

Get fuel up to Carb before getting ready to push

Pushers

Do some back-warming exercises

Stand with one foot forward and one back while looking UP as high as you can

Right hand on bumper, left hand on seat back

Lift 5cms up and carry for 1 metre

Pushdown and KEEP PUSHING and KEEP LOOKING UP.

Don’t let the driver trap your hand in the seat

When the kart start, KEEP RUNNING and checking behind you until you get off the track

Drivers

Lean forward over the steering wheel

‘Hover’ your hand over inlet

Once rolling, sit back in the seat (but let pushers ‘escape’)

Until the engine fires

0-5 metres no choke, slight throttle setting

6-30 metres, full choke and FULL throttle

30+ metres, no choke but FULL throttle

Once it fires, REDUCE THROTTLE but ‘hover’ hand over the inlet!

Ian Turner (ITPRO)

Email: [email protected]

Last updated byrpuddle on March 15, 2021
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