Many 2-cycle engines have problems and are sent to the junk yard before their time. Typical problems include hard starting, rough running, a need to adjust the carburetor during use to keep the engine from stalling, a need to rev the engine to keep it from dying, and not starting at all.

I will assume the user knows to replace the spark plug regularly, to use fresh fuel, and to replace or clean the air filter.

With time and normal vibration, the screws that seal the crankcase from air leaks loosen just a little and air gets into the engine through leaks in the crankcase gaskets.

First check the mounting screws for the carburetor and tighten them. Then go to the screws that hold the cylinder head to the crankcase body and those that cover the end where the crankshaft comes out of the engine. See the yellow circles on this photo of a weed whacker engine. If any of these screws loosen as little as a quarter of a turn air begins to leak into the engine and the fuel/air mixture either is not pushed into the engine on the piston's downstroke or it becomes too lean for the engine to run by pulling in extra air during the piston's upstroke.

After about ten years of use, no amount of tightening on these screws will make a dead engine run. Chances are the gaskets have become hardened beyond their ability to seal the engine. Dismantle the engine completely and install new gaskets. You may not be able to buy the proper gaskets, but you can buy a sheet of gasket material. Use the old gaskets or the engine castings as a pattern to cut new gaskets. Your engine will run like new again.

Step 1: Clean the exhaust ports, too.

Remove the muffler. The exhaust ports are under it. In time carbon residue from the burned oil in the fuel mixture begins to close off the exhaust ports. An engine is an air pump. What cannot get out blocks what needs to get in. Move the piston to the downstroke position (most distant position away from the spark plug) and knock off carbon deposits with a screwdriver. Turn the engine over by hand a few times to blow the carbon granules out of the engine.

Once I used our small 2-cycle garden tiller. After ten minutes the engine siezed and stopped. I had mixed 2-cycle oil with the gasoline, but it was old by the time I was using it. I found advice on the Internet that said to let the engine cool. Then use a wrench with a long handle to slowly turn the engine over. Turn in the same direction, not back and forth. That engine still works very well, although I am sure it suffered a little. Lesson learned: always use freshly mixed fuel.

When a gasoline engine of any kind will sit unused for any length of time, drain the fuel from the tank and run the engine until all remaining fuel in the system has been burned through the engine. This prevents gums and varnishes from closing off small openings.


Good day mr. Phil! I have this honda dio 2 stroke 50cc engine, it stocked in a very long time, i would like to restore it, so i cleaned the carburetor change the cdi,ignition coil, sparkplug and statorcoil, i change the oil in the oil tank and a fresh fuel, so it has a fresh fuel,full compression, good spark, and propper lubrication, but it wouldnt start i change the cylinder gasket but it wouldnt start the engine, i am so confused right now what should i do? Thanks!
My engine would no longer start ten years after I bought it. Gaskets between the halves of the crankcase and between the carburetor and the crankcase hardened from age and no longer sealed. When I changed all of the gaskets the engine ran again.
So i must overhaul the engine and replace all the gasket
<p>If the engine is more than ten years old, I would definitely replace all gaskets. I think it is very likely the cure to your problem. All you need for the engine not to start is just a little too much air getting into the crankcase and making the mixture too lean. Gaskets hardened from age make that very possible. I bought some gasket material and made my own gaskets. </p>
Thank you mr. Phil. My engine is running very smooth after i replaced all the gasket. Thank you very much sir and god bless!
<p>I am very happy for you. Thank you for the report. Repair manuals do not mention old gaskets that no longer seal properly. I suppose you are not expected to keep your engine, but to buy a new one.</p>
<p>hi, i have a craftsman leaf blower (358797310) that i just changed the spark arrestor gaskets on. now when i turn it on, it blows blue smoke and has a high pitch noise.</p>
<p>I do not have any experience with what you are asking. Can you adjust the carburetor to reduce or eliminate the blue smoke? Is the high pitch noise mechanical, like a dry bearing, or a whistling, like air rushing through a confined space? </p>
Its a whistling noise. I will go ahead and try to adjust the carburetor for the blue smoke.
<p>Is there any possibility the gasket can be installed upside down? I know that is impossible in many applications, but I have heard of it happening in other applications. A gasket upside down could plug some passageways and open others, which might make a whistling noise. </p>
<p>Hi there. I have a 2 Stroke Tecumseh 3.5 mower. I loaned it to somebody who then put straight gasoline into it with no oil and then called to say its not running properly. I drained it out when I got it back and refuelled with proper mixture. Now when I use full throttle it starts sounding like a Helicopter and starts billowing out white smoke. Any ideas where I might start looking for the problem? I am a newbie when it comes to 2 stroke engines. Many Thanks</p>
I am sorry to hear of your engine problem. I would not lend my things to that friend again, unless the friend offers to pay for any damage to your engine caused by his error.<br><br>4-cycle engines have oil in the crankcase to lubricate moving parts, especially the contact between the piston rings and the cylinder walls. 2-cycle engines get their lubrication from the special oil mixed with the gasoline. When that oil is not present in the fuel in the proper mixture, the danger is that destructive wear will occur in the engine quickly. A compression check would give a strong clue about the extent of damage. Once damage happens, there is no economical way to restore the engine. You could check on the cost of honing the cylinder walls and installing new piston rings, but it may be cheaper to buy a new engine. If you choose to buy a new engine, look into a short block. It is the bulk on the engine and contains all moving parts, but does not include still useful things like the engine head, the ignition parts, and the carburetor. You would need to install those on the short block with new gaskets where parts need to seal. <br><br>One choice you have would be to use the engine as is, but not use wide open speeds at which you get the visible smoke. If there is scoring on the cylinder walls, the looseness it causes with the piston could cause more wear faster than normal. <br><br>You could remove the head for a visual inspection of the cylinder walls, but will need to install a new head gasket and torque the bolts to the proper amount. You or a repair shop may have a fiber optics device that allows you to peek inside through the hole for the spark plug. <br><br>I wish I had better news for you.
<p>8 hp Suzuki outboard motor spits out oil in the cooling water when I first start the motor. Motor runs great and starts easily. Is the oil a sign of problems coming in the future? Could this be a sign of the head bolts becoming loose?</p>
Welcome to Instructsbles. I have no experience with outboard boat motors. I did a little search on the Internet and learned some outboard engines have an oil tank and the oil system can be out of adjustment, but I think that dealt more with combustion and your question deals more with water cooling. It may be someone else will see your question and give you a better answer. There appear to be Internet fora for outboard owners to discuss problems like yours with other owners. <br><br>Instructsbles is a great site for sharing. Often I came to it looking for an answer, but found none. Then I had to develop my own solution I later posted. One such case concerned an electronic flyswatter that did not spark. Posting what I have done also allows me to have a detailed record for the next time I need to do the same thing, but have forgotten a detail or two.
<p>Hi Phil B, <br></p><p>I am a newbie with very little knowledge of 2 <br>stroke engines, just bought a new Hyundai 33 cc 2 stroke multi tool, <br>every thing was fine on all the heads and then it just stopped. Got it <br>going again but if i pull the accelerator trigger there is no power it <br>slows down and stops. This is brand new so the only thing i can think of<br> is the petrol /2 stroke oil mix. on the instructions it says 40:1 for <br>synthetic and 20:1 for mineral. I bought new petrol and new 2 stroke <br>garden oil that is green, its ingredients says mineral so I put it in at<br> 20:1 was i right to do this and is this the problem?</p><p>any help would be great before I contact the shop I bought it in and look like a fool if it is the petrol/2 stroke oil mix</p><p>regards</p><p>John</p>
Have you taken the spark plug out to se if it is reasonably clean or fouled with carbon? Does the crankshaft turn over smoothly? Does the cap on the gasoline tank allow air to get back into the tank so the engine does not get a vapor lock? In some of the comments I linked a diagnostic site for small engines. It is set up like a flow chart. You have to work through it in logical steps until you find the problem. <br><br>One consideration with new equipment is that if you tweak it, you may void your warranty.<br><br>I wish I could be of more help.
Thanks Phil for the answer. <br>I will have a look and see if I can find the link and run through it over the weekend. I have since found out that the 2 stroke oil is in fact synthetic so I have definitely mixed it wrong even though it is not marked on the bottle. I have since drained the tank and added the same amount of petrol again to bring the mix back to where it should be.<br>regards<br><br>John<br><br>
<p>I retrieved the troubleshooting link. </p><p><a href="http://www.smallengineadvisor.com/members/2stroke/main_screen_2S.html">http://www.smallengineadvisor.com/members/2stroke/...</a></p><p>We had a little 2-cycle roto-tiller. I used some old fuel mixed with 2-cycle oil in it, but the fuel should have been discarded. The engine stopped abruptly after running ten minutes or so. It had seized. I checked on-line. I think I put a spoonful of light oil into the spark plug hole. I do remember instructions were to turn the engine slowly with s large wrench, but in one direction only--no back and forth. It loosened and seemed to run fine after I got some fresh fuel properly mixed. I am sure I added some wear to the engine. </p>
The point condenser has not been changed recently. I don't even know if it can be adjusted. its a fairly simple motor. Any other suggestions that would cause a yellow spark? Spark plug wire or anything else?
<p>It has been a long time since I have dealt with points and condensers, but points become pitted after lots of use and need to be replaced. The pitting also causes the engine timing to change. Condensers can become weak. Sometimes they are even shorted from the factory, although that is rare. It is pretty difficult to get a good blue spark unless the points, condenser, and engine timing are good. </p><p>There was also a time when points were in general use, but pointless ignition systems were coming into general use. Some people made devices to eliminate the points and condenser on engines that normally used them. On a fluke, you may be able to find one of those devices. I had a little module like that for a 1970 Lawn Boy 2-cycle push lawnmower. You probably want to find new points and condenser for your Cushman engine. Perhaps Cushman still makes them available. You will need specs. on the proper gap for the points, too. It may be there is no separate timing setting. I do not know. </p>
Thank you. I will check those.
<p>I have a 1984 ezgo golf cart with a 2 stroke engine. It has ran fine for many years. Then one day it just stopped. It has spark, fuel, and turns over, but wont start. It wont even start with starting fluid. </p>
Welcome to Instructables. Does your engine still have sufficient compression? Does it need a new spark plug? An old plug will show spark at atmospheric pressure, but it fails at the pressure of engine compression?
Yes. the compression is 110. The plug is new, but the spark is yellow. I was told it should be blue. Any suggestions?
<p>Yes, you do need a blue spark. Have the points and condenser been changed anytime recently? Can you get new points and condenser for that motor? The engine timing needs to be set correctly, too.</p>
Hi I bought a 99 Polaris trail boss 250 2 stroke it run nice but it leaks gas for the engine block.. And also i can't floor it or it dies right away
It sounds like the float in your carburetor is heavy and needs to be replaced. A heavy float does not stop the flow of gas into the carburetor. It flows out of the engine block and makes the engine run so rough that it stumbles and dies. Even foam plastic floats absorb gasoline and become heavy.
<p>Hi. I purchased a roughhouse 50 scooter for my son couple months ago. The scooter is having some issues. The mechanic is telling me that we used the wrong oil for it. We used 2-cycle oil and he told us we had to use 2 strokes... I thought it was the same thing? Is there a difference?</p>
Two stroke has always meant two cycle in everything I have ever seen. Is there a lot of carbon deposit on the spark plug when you take it out?
<p>It is at the dealership right now so I cannot check...</p>
My 2 stroke 49cc bike will start but will shut off almost instantly. What is wrong?
Fuel starvation? Perhaps the engine gets enough fuel to start with the choke on, but as soon as it starts the choke may, perhaps, go off and something blocks enough fuel from getting to the engine, or there are air leaks through poorly sealing gaskets and the engine dies for lack of properly mixed fuel.
<p>I just upgraded my 49cc 2 stroke and the exhaust pipe I got is not letting my engine start, I take it off it fires up, is the pipe too short?</p>
I do not know. Is there a blockage in your exhaust system that restricts flow, like a piece of packaging? Can you blow freely through it? The engine cannot run if the exhaust cannot escape, as you likely know.
<p>no blew it out its clear, just downloaded 2 stroke wizard tuned pipe pro5, going to build my own. </p>
<p>phil b, I just tried putting the stock exhaust on and it wont start, so i'm assuming it's all in the pipe. I've been working on this upgrade, for a month and half, reading and learning, to figure it out, I cant find a manual, I don't even know who makes the engine. I bought a scooter x xracer.</p>
<p>its a tecumseh 1589A and it has a strange reed port near top of cylinder on side have no clue what its for almost like a compression reducer! reeds seem ok. i'm assuming crank seals leak i see some wetness there. points look fine has good spark gap is 16 thousands. cant get it to fire except with what seems a chance perfect mixture and then it runs for 1 sec weakly. piston ring is not carboned up.</p>
Thank you for the additional information. You mentioned spark timing. There is not much opportunity to adjust timing on those engines because the timing is set by a flywheel key. The gap on the points could cause a change in timing, but that seems to be good. You certainly could have worn crankshaft seals. Yet, you said the plug appears to be wet after a period of cranking. You seem to be checking all of the right things. I do not have any better ideas than the things you have been checking. Unfortunately, all I can say is to check things one by one and try to eliminate all you can until you find the problem.
<p>i got i to run by raising the pressure required to open the compression releif port. (reed)i dont know if that means compression was too low for 0 weather or what? now i just have to put carb on and see if that's working right. it only has 1 jet adjustment compared to the 2 i am used to. </p>
<p>Thank you for the report. I never would have guessed. I used someone's Chainsaw, but do not remember if it was Stihk or Husqvarna, and it had a compression relief valve for cranking the engine. It sounds like your engine was low on compression. Thank you for the education, </p>
the points holder has slotted bolt holes but looks like the bolts have never been disturbed. its a yardman bantam snowblower from 79 i believe. am going to double u on the reed that releases compression to see if that helps. also do a comparative compression check. if the extra pressure makes it start/run i could plug that hole permanently.
<p>got an old 2stroke snowblower with 2 or 3 hp engine and trying to get it started. compression seems ok spark pug is clean and nice blue spark . fuel line not hooked up i am just using spray start to try it out before investing any more time in blower rebuild. it did run just one time but very weakly is the only way i can describe it no feeling of power. plug gets wet does not pop/sputter at all! tried another plug already. almost acts as if timing is wrong?</p>
<p>I have a Ryobi RGBV3100 2 cycle leaf blower about 12 years old.Over the past few years the starter cord has been jamming but when the machine eventually starts it runs well.A few weeks ago the starter cord broke.I have dismantled the machine(lots of screws on this model) and the muffler and carburettor are off the machine and the fuel tank drained.In its stripped down state and with the spark plug removed</p><p>a pull on the new starter cord turns over the engine easily.However as soon as I replace the spark plug the starter cord starts jamming after about six inches.</p><p>Any ideas for a solution.</p>
<p>I found on my RIOBI 2 stroke that my &quot;garden engineer&quot; decided to use not just regular motor oil.... but used motor oil in place of 2 stroke oil in the petrol mix.</p><p>The motor started but died as soon as I tried revving it.</p><p>I removed the muffler to check for carbon buildup but didn't find much, I did however find the whole muffler were clogged up with carbon and oil. Running the motor without the muffler, caused it to run fine.</p><p>Now to see if I can dissolve the residue or buy a new muffler.....??? </p>
I once thought I would save by using motor oil instead of 2-cycle oil. The engine was a dozen years old, anyway. The engine quit. I found lots of hardened carbon in the rings. I ended up buying a new short block. I wish you well.
It sounds like something is obstructing the movement of the piston, but it comes and goes with the presence of the spark plug. A physical object inside the cylinder could obstruct the piston. So could too much liquid inside the cylinder. Liquid would make more sense, but that does not seem likely with the carburetor removed. Extra liquid should also spew out when the engine is cranked with no spark plug, at least enough to indicate its presence. I did once work on a friend's 4-cycle roto tiller. It had a piece of stray metal inside the cylinder. I have no idea how it got there. The piece of metal was a little battered. Have you turned the engine with the spark plug hole down to see if any liquid flows out? (If yu are getting liquid into the cylinder, it would indicate a carburetor problem, probably a heavy float. Even plastic floats absorb gasoline over time and become heavy. It seems counter-intuitive, but I had it happen on a car I drove.
<p> Thanks Phil B for your comments.Yesterday I turned the engine upside down so that</p><p> the plug hole was on top.I then moved the piston down so it was as far as possible from the plug hole.I then squirted WD40 several times down the hole on to the cylinder/piston, inserted the plug and left the engine upside down overnight.This morning I took the plug out and easily turned the engine over about 30 times in the hope of moving the WD40 around.I then replaced the plug and was able to move jerkily through the full length of the starter string,I will follow the same procedure for tonight in the hope that the engine will</p><p>turn over less jerkily tomorrow with the plug in.I'll also check for stray metal.The fuel tank is still empty although I have reinstalled the muffler and carburetor and I will have to replace the brittle fuel lines.I'm wondering whether the problem has been caused by using fuel/oil</p><p>in the ratio of 50:1 (as recommended by an engine mechanic) instead of 25:1</p><p>specified in the manual.I'll report tomorrow.Thanks again.</p>
<p>if the range of motion improves with a light lubricant sprayed into the cylinder the problem may be related to deposits or roughness on the cylinder wall near the top of the cylinder. Such roughness could be like a mechanical blockage.</p>
<p>The range of motion improved slightly again.No loose metal in the cylinder.The</p><p>incorrect fuel mixture may have caused some deposits to build up on the cylinder wall.</p><p>I have ordered replacement fuel lines ,filter etc.When I return from holidays in about a month.I will instal the new lines,put some fresh fuel (25:1 ratio) in and</p><p>hopefully will be able to get sufficient speed on the starter line to get the engine to fire.</p><p>Not worthwhile to spend too much on an old machine.I will let you know</p><p>the result.</p>
<p>if the crankshaft is broken then the engine can start or not ab ot chainsaws</p>

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