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? Answer: It sounds like something's rubbing or broken in the engine. It could be a serious failure like a broken connecting rod which you can check by removing the crankcase cover or possibly a loose magneto coil rubbing against the flywheel, requiring the fixings to be tightened, ensuring the legs of the coil's former are at the correct spacing distance from the flywheel magnets.
Question: Why is it difficult to pull the starter cord but easy with the plug removed? Answer: A clogged exhaust can make it difficult to pull the starter cord. Over time, residue from combustion can clog exhaust ports, spark arrestor screen and muffler. Also, there could be a hydraulic lock with fuel in the cylinder. If the engine doesn't have a clutch, whatever is down the line from the engine may be sticking and making pull starting difficult. Thee could also be an issue with the recoil starter, causing the rope, spring mechanism or starter pulley to jam.
Answer: No. It's fixed to the engine. However, the pickup fuel line moves around in the tank so that it's always under the surface of the fuel, even if the tank isn't full. The line that sucks up fuel in the tank is supposed to move around when the trimmer is used at different orientations.
If it doesn't do this, if the fuel is low in the tank when the trimmer is used at an angle, or upside down, air can get sucked into the line and stall the engine. On initial starting, a trimmer can splutter and stall with choke off until it warms up and reaches speed and the carburetor fills properly. Try starting and running with choke back on again or half on for several seconds before turning the choke back off. See the guide for more details.
Question: I have started using my Mitox 2-stroke petrol strimmer to cut down very tall, dense grass. So I've fitted the heaviest duty nylon line, and the strimmer is working very hard. Yesterday was very humid, and I noticed water coming from the exhaust in quite large amounts. I initially thought the petrol tank has split, but was reassured to find that the fluid was dirty water.
Is this normal? Answer: A by-product of combustion is water vapor, but you normally only see this on frosty days from, e. It's possible as the exhaust gasses expand, the temperature drops to the degree that water vapor condenses out in the humid atmosphere.
Temperature can drop substantially as gas expands, hence the vapor trails on the wings of aircraft in low-pressure regions of the wing, or you'll notice how an aerosol can get really cold as the spray is released. Another example is when you blow out air from your mouth onto your hand. If your mouth is wide open it feels warm, but if you blow out with your lips tightly closed, the air feels cold, because of the temperature drops as it expands on exit.
Moisture will also condense when the air is compressed because it can only hold a certain mass of water per volume at a specific temperature. So this is why water condenses in the tank of an air compressor, as molecules of H2O get squashed together when the air is compressed. If the trimmer is 4-stroke, you can follow the procedure outlined in Jacks Small Engines here, or check your manual for the procedure for your specific model.
If you can give me the model number, I can check the details. Question: My string trimmer's starter rope has no tension on it. Has it disconnected from something? Hi, thanks for the quick reply and taking the time to look into it. Mine doesn't have any marking either but I was hoping your manual had a part diagram with part numbers.
Mine didn't. I'll call Yardworks but I'm afraid I'll be told that it's discontinued and can't help me. I'll keep Googling and maybe I'll get lucky. BTW, reason I need a new carb is after cleaning it in my ultrasonic tank and rinsing it, I used compressed air to get the water out.
Don't know if you know this but there is a small o-ring within that cross air hole. The compress air took it out and there is no way to put it back. That part doesn't come off either so my carb is having more issues than it did before messing with it The only thing I can suggest is to try and blow out any flakes that could be lodged in passage ways in the carb with an air compressor blow gun. Blow out the jet in the carb too. Check the valve in the primer button is clear too and pushing air out through the centre and not sucking it in from the tank through the flappy edges I describe in the article.
Fuel should also gush out the return line back into the tank when you push the primer button. Great article, tons of good information. Didn't answer the question about if it is normal for the primer bulb to have a large air bubble no matter how many times you press it in.
My Blue Max was new, purchased prior to my shoulder surgery so it wasn't unboxed until a year later. It started once. It would idle but never gut a single weed as would conked out when the trigger was depressed. Due to 2nd shoulder surgery I drained the gas out and put it away.
Now this August I did all the basic including taking apart and cleaning the carb and blowing out the gas filter. My findings were only that there were black gaskets flakes like from a dirty factory that made the carburetors. The carb screen was clean but flakes beyond in other areas. Put gas in and it almost started then nothing after many pulls.
I have a tack for my chainsaw and lawnmower repairs. A pull yields an RPM of Last week it would run if you feed it gas with an eye dropper directly into the carburetor. I figured cleaning the carb would solve the problem even though there are zero hours on the machine. Hope you can help. Unfortunately there are no markings on my carb. I can't find any references online for your carb either, but I've tweeted Canadian Tire and they may be able to help.
Hi, thanks for the great article. It really explains how this little carb is working and that video you linked was very informative as well. I can't find a match for a carb anywhere online. Would you have its part number or better yet, would you know the part number of the carb for this Yardworks trimmer? The exhaust could be clogged or the recoil starter could be rubbing creating friction which would add to the normal force required for starting.
Some strimmers have decompression valves which need to be pressed also when starting. Have a look at this discussion:. My strimmer cut out whilst using it.
I tried restarting it but the pull chord was very stiff. When the spark plug is removed everything moves smoothly. Any ideas? Interesting article. Since most of the string trimmers and other such handheld devices are having 2-stroke engines predominantly. Is there a market shift from towards 4 stroke from 2 stroke in any handheld equipment you see?
This may have resolved the problem temporarily allowing air into the tank, but there could still be an issue with the check valve located in the cap or body of the tank. Probably a good idea to examine it to see if the internal valve surfaces are stuck together or there's stuff stuck in it.
Hi Eugene. Thanks for the advice. I unscrewed the fuel cap and that has sorted the problem. I thought it should be something simple as I always use the correct fuel mix and being almost new very unlikely to be a problem with the carb. Great article. This model seems to have a clutch. Is it possible that the cutting head or shaft are seized and this stalls the engine when it's revved?
Hi Eugene, thanks for your comments. Yes we've adjusted the high speed mixture - but no joy there ok we can get it going better, but it still cuts out. We've also tried the fuel cap trick - again no difference. We've also tried the gentle squeeze trick - again no joy. Interested to read your comments on the coil - so maybe this could e the culprit? But yes the issue is just with throttling - it idles fine.
It's an odd one as we have changed everything else and cleaned meticulously. I have a Stihl Kombi engine which is only a couple of months old. It starts ok. Wondered what is the most likely problem. Maybe the coil just ceases to function due to electrical break down when the engine speeds up and it's sparking more often.
I don't know. If the engine cuts out when throttled, it's due to fuel starvation for whatever reason. Is there a high speed mixture screw that you can adjust? Have you tried loosening the fuel tank cap in case the tank isn't venting and letting air in as fuel leaves to feed the carburetor? Sometimes my strimmer dies on throttling up, so after turning off the choke, I gradually squeeze the throttle and let it reach speed and turn the choke back on half way if it starts spluttering.
Great article btw - So have a Husq ld strimmer which dies after throttling. Have replaced carb, fuel filter, fuel lines, spark, filter and cleaned it top to bottom. I can now start it and it will idle, but as soon as I try to throttle it dies. I have repeatedly adjusted the fine tune screws which don't seem to help occasionally it may run for 60 secs, but then dies.
Fuel is new - everything new. Have taken it to local 'fixer' who suggested that ignition coil module 'may be' required. My question is that as it starts, idles etc - would the coil actually have any bearing on the running of the engine? Happy to hear if so, but don't want to pay for someething to be replaced if there is no way it could be the problem?
Sorry I don't. Just wondering if you had a motor parts list. Mine is identical to yours but a different brand still made in China and of course I can't find anything on mine. Really excellent article you done. Really appreciate it. I have an issue with my trimmer at the moment. I think what happens is that the carburettor leaks in storage.
I'm not sure of what exactly happens because I store it with the tank on it's back, so possibly as temperature rises in the shed, this causes fuel to expand in the lines and dribble out past the metering needle. Anyway with fuel flooded into the carburetor and crankcase, it's difficult to start. I've just tested the tank Geez, fuel tastes awful and there is a leak in it.
I feel like breaking into the tip to get one of those damn tanks! J Joe Carroll Unregistered. Switch to Threaded Mode. Show Likes. General Discussion Forum. Off Topics. Joke of the day. OutdoorKing Showcase. Show and Tell. Power Equipment Mishaps and Funny Stuff. Repairs and Maintenance. Questions on Engines. Questions On Honda Engines. Questions On Rover Engines. Questions On Robin Subaru Engines. Questions on Other Engines. Two Stroke Lawn Mower Frames.
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Collectors Events including Swap Meets. I have a Ryobi trimmer that won't start. As part of the diagnosis, I cleaned the carb. In doing so, I did find some gunk - unfortunately it still won't start, so diagnosis is still ongoing.
In any case, while cleaning the carb, I used compressed air, and blew out the screen. At the time I thought I saw something fly out, but I didn't clue into the fact that it was the screen. Now I can't find it. What are the consequences of running without the screen? I will try to see if I can get a replacement screen at the local shop, but I suspect I'll need a whole new carb.
Nothing more frusturating for the average individual than a 2 cycle engine that will note start or run well.. If you have compression and Spark those two cycles run very well with a bit of Carb work that anyone can do.
That surface so important to proper flapper valve seating is a rough sanded factory surface comparable to a grit sand job. Just look at those machining marks in there. Take apart only that flapper valve side of the Carp.
Then take and polish that entire Aluminum surface with a grit Auto polishing paper glued to a flat board. The flapper valves will it seat properly and 2 cycle engines become easy starters. Many of our test engines starting with one or two pulls 5 years later. Don't be fooled by Carb replacement garble Resurface that Aluminum surface as above and your starting problems will be gone. I heard that carb cleaner will ruin the plastic and rubber gaskets and O-rings in a carburetor.
Is that true? If so, please update the instructions with that warning. I have a Blue Max Chainsaw and it was running pretty well until yesterday, I think I mixed too-rich fuel mixture. It was almost stalling when I gave it gas, then eventually it gave up the ghost. I have replaced the spark plug, fuel filter, checked the muffler and spark arrestor and cleaned everything up fairly well, but it will not start, period.
I even used ether starting spray, which usually starts anything, but nada. My carburetor does not look anything like the one in the instructions. It's smaller, and it look pretty clean. Should I take it out and clean?? I do get a spark across the plug, btw. Reply 6 years ago. I'd say remove the exhaust and apply heat using a torch first before dissembling the carb. I have a craftsmano weed eater with out a primer bulb,carburetor been off the the unite for a while,I've replaced the carb,but now I don't remminber how the fuel li.
I recently did this for a Stihl trimmer, which has a Walbro carb though it looks just like the one in this instructable. I bought a parts kit from a location dealership and did pretty much everything explained here, except replaced old parts with new.
For me, the hard part is tuning the thing afterward. I still haven't been able to get it to run right and idle right I can get it to do one or the other , even after finding the factory tuning specs online and following that. Reply 10 years ago on Introduction. There Is one screw for idle I and one for everything from idle and hirer H.
Set the idle first than the high, after its warmed up. If you Messed up it totally, turn all in to the right than back about 1 - 1. Then go from there plus or -. Tune in order of lowest RPM to Highest. Also check your air filter, gas line, and important and often missed - the fuel tank breather tube I have a Stihl chain saw that always has problems with breather tube.
A bad breather tube creates a vacuum lock, their by stopping fuel flow. Sign in Sign in with Password. Cart Shopping Cart 0 item s in your cart. Restore a saved shopping cart. Preferred Partners of. Trimmer: Engine Will Idle But Dies At Full Throttle If your trimmer engine idles, but stalls on throttle, check the following parts: the gasket, primer bulb, fuel filter, air filter, fuel vent, fuel line, and carburetor.
The carburetor mixes the air and fuel together to the proper ratio for combustion. Locate the carburetor underneath the air filter. What follows is a guide to fine-tuning your carburetor, as a poorly adjusted carburetor can contribute to your symptom. Remove covers to gain access to the carburetor.
Remove the air cleaner cap and filter, checking for any obstructions in the way that could block air flow, starving the engine of oxygen. Locate the adjustment screws. To adjust the carburetor, start with both screws backed out 2 turns from the closed position. One should be idle mix and the other should be high speed. Start the engine and let it warm up for 5 minutes.
You may have to keep the throttle open a bit. Slowly turn in Next, hold the throttle wide open, and slowly turn in the high speed, until it really starts to smooth out and rev high, and starts screaming, then back this out until it starts to run rough or slows down. Turn it back in to midway between these two positions.
Keep playing with the low speed needle until you get rapid immediate response from the throttle, and good idle with the idle adjustment. Backing it out will allow more fuel when under a load, and keep your 2-cycle motor from running too lean.
Put a load on it and just tweak the settings a hair at a time. Most will start and run with both screws open 2 turns. Don't close the high speed off any more than necessary, no matter how well it runs.
Some carburetors are fixed, meaning they have no adjustments. Clean out the carburetor with carburetor cleaner. They can become gummed up easily in 2-stroke engines. Find your Carburetors here. Over time the air filter will need to be replaced as it becomes clogged with small particles and debris, starving the engine of air, causing a loss in power. Locate the air filter cover on top of the carburetor and remove it.
It may be attached by screws or just a tab.
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