How does a whipper snipper motor work

A two stroke engine is an engine that does not have valves, or a specified lubrication system. A two stroke engine is very simple, much simpler than the 4-stroke engine.

It has very few working parts and is very light. This means that there is very little maintenance required and it is much cheaper to manufacture. They are also used in shorter time increments, so the problem of pollution is not as serious. The fuel and oil mixture running through the engine is what lubricates the parts, however, because it is not a specified lubrication system, these engines usually wear down quicker.

This process can also be known by 2 kinds of strokes, the compression stroke and the power stroke. The power stroke is all of the other steps, the steps that actually produce the explosion and create the power.

This is also my 2nd Instructable so please be constructive and supportive. This step involves making the mounting brackets for the motor, this is probably the most crucial step and also the longest, not because of the fabrication takes bout 30mins but the thinking and fiddling around. This took me about about an afternoon and night wondering whether I needed more or less or stronger supports. I then just came up with a 2 support plan and stuck with.

I forgot to take a photo but its pretty simple. I had lots of ideas about this, including using bike pegs, making my own, scooter wheels etc I saw someone use a socket and it slipped against the wheel and didn't work at all if he went through a puddle I had sum bike pegs I was going to use but they had imperial threads and my clutch used a metric thread and I didn't want to make an adapter so I decided to make my own.

I needed a lathe to make my own but so dad knew a bloke with one and he made it for me. I only just had enough throttle cable to have a squeeze lever throttle like on jetski's, if you don't have enough throttle cable as most of the newer whipper snippers use arm linkages and not cable, you will have to get a longer cable and rig it up.

I imagine it would be a pain to do and thats why I made do with my short cable. This is the fun bit. If u used an old motor like mine that is very unreliable and crappy, it would be best to carry out some maintenance on your engine.

Also unlike me it would be wise to put brakes on your bike!!! I got quite a scare going into a busy intersection with thongs flip flops, sandals as my only brake. Also check the legality of these kinds of mods, in NSW, Aust, to be legal it must be under watts of power and under 25cc or something.

My bike when the engine was running nice did 40kmh easy on flat. Thanks for reading my instructable and please vote for it in the Park Tool Bike contest! I am building one of these, but i ran into a problem. If your unit does not have an internal fuel filter, follow the fuel line from the tank leading to the carburetor and locate the filter. Remove the filter by twisting and gently pulling the lines free and install a new filter. Make sure you check for an arrow on the fuel filter indicating the direction of flow.

The arrow should point towards the carburetor. Find your Fuel Filters here. The purpose of a gasket is to seal pieces tightly together, sealing off air and fluids from entering areas where they are not supposed to enter or exit. To check this, start by removing the air filter then loosen carburetor bolts.

Disconnect the fuel line and remove any linkages depending on your clearance to remove the gasket. Check the condition of the gasket; look for tears or any indications of leaks. Clean off both mounting surfaces. The gasket will need to be replaced regardless of condition, as they can only be used once. Re-install the carburetor and hook up any linkages you removed, and reconnect the fuel line.

Re-install the air filter housing with air filter. Find your Gaskets here. Check the spark plug by carefully removing the spark plug wire, as they are fragile. Remove the spark plug and check its condition. You can clean off the plug and re-install it. Make sure you also check for any deposits, breakage, melted parts, or corrosion. If the engine spends most of its time running at high RPMs, try installing a cooler running plug to dissipate heat more quickly.

Find your Spark Plugs here. The primer bulb primes the carburetor with fuel for easier cold start ups, to get the engine to run. Seeing leaking gas is a good indicator as well hearing air rushing in when pushing on the bulb. To replace it, simply pull it off with a pair of pliers. Next, reach back into where the bulb came off, grab the clip and pull out.

Clean out the housing. Put the new clip on the primer bulb with tabs facing out. Then use a socket that fits over the primer bulb and push into the housing, giving a gentle tap with a rubber mallet if necessary. Make sure the metal clip is as far as it can go without damaging the Make sure the metal clip is as far as it can go without damaging the primer bulb. This procedure could vary on different models but are all similar.

Resistance should be less than 1 ohm with the switch in the off position. Ideally you should detach one of the wires from the switch when testing. Useful for checking voltage, current, continuity, and fuses. Unlike lawn mowers and other such yard equipment which is normally used in one orientation, trimmers, chainsaws, and hedge cutters must be used at all sorts of angles. A lawn mower has a vent in the gas tank cap to allow air into the tank as gas leaves it. If the tank wasn't vented to atmospheric pressure, this would restrict the flow of gas out of the tank.

Turn a large soda bottle filled with water upside down and you'll see what I mean. If you've ever emptied a 55 gallon oil drum, you'll know they have a secondary bung which needs to be loosened to vent the drum, allowing air to flow in and enabling smooth flow from the main outlet during emptying. On a lawn mower, the vent is just a hole with a fiber or plastic baffle inside the cap to stop gas splashing out.

This isn't good enough on a trimmer if the tank is turned upside down, so a one way valve is used also called a check or non-return valve. The valve allows air in but gas can't leak back out.

This could get clogged with dirt or the internal surfaces of the passageway in the valves could be stuck together, so try starting the engine with the cap slightly loosened keep the tank upright to see if it makes any difference. To clean the valve, gently slide a small flat blade jeweler's screwdriver into it to make sure its clear make sure it's small diameter to prevent damage.

I couldn't get access to the back of this valve because a fuel filter was pushed into place. There wasn't a problem with the valve so I didn't go any further.

On my trimmer, the one-way valve is fitted in the gas tank cap. This valve holder has a filter at the back. It seemed to be difficult to prise out and may have been bonded to the holder, so I left it in place. Possibly, although I've never had any problems with clogged filters on my hedge cutter, chain saw, or trimmer, and they have have had hundreds of hours of use.

Whether the filter gets clogged depends on the quality of the gas you get. If you don't take care when filling the tank and allow crap such as dirt and sand into it, it will inevitably end up in the filter. Impurities in two-stroke oil probably accumulate in the filter also. If you can prime the engine and fuel can be seen to return to the tank via the line without the filter, the filter is unlikely to be clogged. The filter is located on the end of the intake fuel line and is replaced rather than cleaned although you could try removing it, wash in hot soapy water, rinse, and allow it to dry before replacing.

If you've checked all the easy things to remedy above, you may need to checkout the carburetor:. Magnetic parts tray. A cloth also stops parts rolling about. Your carburetor may be somewhat different from the one pictured, but the basic principle is the same.

Remove the air filter from the housing and check it for dirt. Wash it in soap and hot water, then squeeze and allow to air-dry. If you're just removing the air filter to clean it without doing any further maintenance or troubleshooting, it's always a good idea to close the choke beforehand to prevent any dirt from getting into the carburetor.

Ensure the filter is free of dirt. Wash if necessary. The choke is simply a plate which covers the air intake. When it is closed, the engine sucks in a richer mixture i. This makes for easier starting. The carburetor exposed: Next, the fuel lines and throttle cable must be removed.

Mark the fuel lines before removal. A "Tippex" style correction pen is useful for doing this. Don't stretch the fuel lines by pulling them. Instead, try pulling them gently while pushing with a flat bladed screwdriver or needle nose pliers against the edge of the lines. It's probably okay to blow over the outer surface of the assembled carburetor to remove grime, but keep the nozzle of the blowgun away from any openings.

Wear safety glasses to protect your eyes from grime and small parts which could get blown up towards your face. It's also a good idea to take lots of photos at every stage of disassembly just like I did here, in case you forget how to put everything back together!

Remove the primer bulb retaining plate. Trimmers either have a primer button mounted on the carburetor or a remote primer. To check whether the priming system is working, fill the tank so the line with the filter is submerged, but the other return line is above the fuel level. Then try priming. If fuel flows out the return line, the primer bulb and valves are likely working ok.

Primer bulb and one way "umbrella" check valve red piece in center. Check the edges of the valve aren't stuck to the primer body. One-way or check valve. Check there's no dirt stuck in the "duck bill" valve section in the center of the "umbrella" or the internal surfaces of the passageway through it aren't stuck together. With all the holes and passageways in the carburetor, this can be somewhat confusing to work out. Have a look at the photo below. This is the sequence:. Reed valves and fuel pump.

The red numbers are the sequence of ports through which the fuel passes, flowing up through the screen at 1, and exiting down through the metering needle valve at 7 to the reservoir pocket.

Fuel is pumped by pulses of suction from the crankcase acting through an "impulse hole" adjacent to the intake manifold. The pulses of pressure move the membrane backwards and forwards, sucking fuel. Reed valves prevent fuel flowing backwards. Handle this piece with care as it can be easily damaged. Also when you replace any gaskets when re-fitting the carburetor, make sure they are the proper ones and don't block the impulse hole.

Note: In the photo, this appears to be one piece. However if you zoom in, you can see that there are in fact two parts stuck together. Firstly a gasket which makes contact with the numbered part of the carb and secondly a part which has the valves and pump. When reassembling, it's important to replace these in the correct order to prevent leaks. If you have a trimmer made by a well-known manufacturer, the chances are that you will be able to buy a carburetor rebuild kit. This is a collection of parts which can be used to replace components in a carburetor which have become torn, worn out, warped, punctured, coated with hard deposits, or deteriorated in any other way to the extent that cleaning won't help.

The other half of the carburetor. Part of the jet assembly is in the center. The diaphragm. As fuel is used, atmospheric pressure pushes down on the diaphragm, pivoting a rocker arm, lifting a needle valve and allowing more fuel to enter the pocket. Check for holes by holding up against a bright light source. Warping of these delicate parts can also prevent them working properly.

The needle valve seat. Clean this with carburetor cleaner. Clean all surfaces and fuel passageways with a carburetor cleaning aerosol. This removes any gum deposits which can clog pathways and jets.

The screen filter can be difficult to remove without prising up from the edge. This can cause damage, so it's probably best to leave it and spray cleaner down through it.

If you have a compressed air blow gun, you can use it to aid drying. Set parts aside to dry once cleaned. Plastic parts, especially the reed valve piece and diaphragm, should be dried immediately after cleaning as the solvents in carburetor cleaner can be harsh and dissolve the plastic. Using IPA to clean these parts and the metering needle might be a safer option to avoid damage. Avoid bending the reed valves with the force of the jet by spraying gently or resting the piece on a flat surface.

If you find your trimmer leaks fuel when not in use, the problem can be caused by a damaged tip on the metering needle or an accumulation of gum. This can be removed with a cotton bud soaked in isopropyl alcohol IPA. Clean the fuel pathways with carb cleaner. Make sure the outlets are pointed away from your eyes.

Clean all surfaces of the carburetor with carb cleaner. Clean the jet. An air blow gun is invaluable for clearing a complete blockage in the the jet if you don't have any carb cleaner. The muffler exhaust is fitted with a wire spark arrestor screen so you don't set fire to your garden or start a bush fire!

Over time, this collects smuts and can get clogged, reducing power output of the machine. Low smoke two-stroke oil supposedly slows build up of carbon. If you add too much two-stroke oil to your gas, however, the engine will smoke and deposits of soot will accumulate more rapidly.

I have checked this screen on my trimmer every couple of years and have never seen any deposits worth talking about. In any case, you can clean the carbon deposits with an old toothbrush, compressed air, or a small wire brush. Clean the screen with an old tooth brush, wire brush, or compressed air. The high and low speed mixture screws are often indicated by the letters "H" and "L" respectively. These screws adjust the proportion of fuel in the fuel air mix.

Turning them clockwise reduces the amount of fuel in the mix and vice versa. Some trimmers don't have any mixture screws, the proportion being set in the factory. To adjust the "H" screw, first screw it in carefully until it reaches the end of travel.

Then screw back in a little at a time until it runs ok again. This will flood the engine and stop it promptly. You then need to either replace the switch if it's faulty, or reconnect either of the two wires connected to the switch. Usually they break at the points where the wire is terminated by spade clips either at the engine or switch.

This is another problem that can cause difficult starting. To avoid problems next year, drain all fuel from the tank and run the engine until it cuts out. Leaving fuel in the carburetor over winter or when a tool isn't going to be used for a long period can cause everything to stick together, resulting in difficult starting.

Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters. Question: I have a 26cc Chinese hedge trimmer which refuses to start. All the usual checks I have carried out and still no joy.

It has new fuel, new spark plug, new carb, and still not even a kick. There is plenty of spark, fuel and air. Is it possible that the spark timing has moved, and if so how does one check it?

Answer: Yes, it is possible that the flywheel has moved on the shaft and affected timing. There may be a flywheel key which could have sheared allowing the flywheel to shift from the correct position.

A spark should occur when the piston is near the top, dead center TDC , so look into the spark plug hole and check whether the piston is near the top of the cylinder when the magneto coincides with the flywheel magnets.

Another thing you should check is that the crankcase cover if there is one is sealing properly and the gasket is ok. Answer: Lines get stiff and shrink over time from exposure to gas.

Therefore to stop this type of leak, it's a good idea to replace both lines. If you're doing this repair yourself, drain the tank first, then push the lines off the carburetor connections using the side of the blade of a screwdriver. Next, pull them through the grommet and remove them from the tank. Remove the grommet also, ideally using your thumb to peel it out by the edges rather than using a screwdriver which could mark the sealing surfaces, potentially resulting in a leak when it's replaced.

When replacing the lines, feed them through the hole in the tank first with the grommet removed. It's easier to pull lines than push because they stretch and reduce slightly in diameter, whereas they bulge when being pushed. Next replace the grommet in the tank. If you find this difficult, use a screwdriver to poke it in at the edges, but use the side of the screwdriver blade rather than the tip, again to avoid damage. Pull out the lines and connect them to the carburetor inputs, making sure they're the correct way around.

Question: Can you provide a diagram of the diaphragm, needle valve combination in a carburetor? Answer: I don't have a diagram, but if you look below the section in the article "Diaphragm on a Two-Stroke Engine Carburetor", you'll see photos of the arrangement.

Question: My toro weed wacker will only run with full choke. I just put a new carb on. Why is this? Answer: It sounds as if it's starved of fuel and if it were an old carb, I'd suggest the following:. Check that any gaskets between the carb and air filter and carb and intake manifold are ok. There are one or two small holes beside the intake manifold on two-stroke engines, connected to the crankcase. Suction from the crankcase is used to operate the fuel pump in the carb.

Check the fuel line in the tank to make sure there are no splits that could be letting air in and preventing its ability to suck up fuel. Answer: Something could be causing the flywheel to jam, possibly a loose flywheel magneto.

Remove the plug and see if it's easier to pull the starter cord. If it is, check the exhaust and air cleaner to make sure they're not clogged and restricting the flow of exhaust out and mixture flowing in. There may just be high compression on the engine some engines have a compression release that reduces compression and makes it easier to pull start the engine.

Answer: If the valve is like the red one in the photo in the article, it could be because it's stuck, specifically the central "duck bill" part that allows fuel to pass into the reservoir pocket under the diaphragm.

If it stays stuck in, it's the flappy edges that are stuck. Answer: There's very little you can do with the magneto other than making sure the distance from the laminated core to the flywheel is correct and tightening the mounting screws.

Loose connections should be checked and screws tightened on ring crimps. Faulty magnetos that don't produce a spark at the plug always try a plug that you know is working and isn't cracked should be replaced with a new unit. Question: Do you have any possible causes for a dangerously strong recoil on the pull cord? The engine engages, whips the cord back and then the engine cuts. Answer: This can be caused by the engine misfiring at the wrong point in the sequence.

So instead of the plug sparking and the mixture exploding as the mixture is compressed and the piston is about to change direction, ignition occurs prematurely, and the piston gets pushed back "the other way.

Misfiring can be caused by a loose or incorrectly adjusted magnet coil, or a flywheel in the wrong position on the crankshaft due to a damaged flywheel key. Also, poor fuel and air leaks between carburetor and engine can be an issue. Answer: The air filter could be dirty, but it's more likely that something is restricting flow through the carburetor such as a blocked jet. When starting a trimmer, it can be reluctant to run without choke for the first 20 seconds or so until it warms up and get's going and the carburetor reservoir fills with fuel.

So try alternating running it with full choke and no choke until it can run without stalling on no choke. Answer: 4 stroke engines have exhaust valves which can possibly stick.

Question: Why does the starter cord on my string trimmer snap back out of my hand when starting? Answer: This is likely due to misfiring and the engine turning the "wrong way". So it can fire once and pull the rope back. Question: Can you to explain why burned fuel exits by the admission of new mixture into the cylinder? Answer: When the piston descends into the crankcase, it pushes mixture previously admitted into the crankcase up along a passageway into the cylinder.

This flushes burned gasses out of the cylinder. Question: What is the carburetor model shown in your article and can you get a refurbishing kit for it? It's the same as mine. Answer: I had a conversation with a reader called Mike about 15 months ago, and he reckoned the carburetor was a Walbro wyl series carb. Search for "Mike" on the page and you should be able to find it. He got a rebuild kit for the trimmer and it worked ok.

Question: When I pull the starter rope I get a clanking noise. The engine quit like it was fuel starved. Why does this happen?