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.
<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?
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>
I have a chinese 125cc tgb scooter <br>Last night i got to about 90kms and then the scooter died and slowly came to a holt and will not start. Engine electric start is turning over but will not start .please help
I can only say I looked for a discussion of your problem on the Internet. Hard starting after an episode of overheating usually brought concerns about loss of compression due to warped heads, which would explain hard starting after an experience with overheating, the examples I found related to four-cycle engines, <br><br>You may simply need to check the condition of basics related to the engine. In addition to adequate compression, is there a good flow of fresh fuel? Is it properly mixed with clean air? Is there adequate spark delivered at the proper time.?
<p>I have a chinese built chainsaw which has run once, actually ran the fuel tank dry, ever since then I have not been able to start it. Did the usual checks, air filter, plug, fuel mixture, still to no avail. So today I decided to have a look inside, took off the exhaust chamber and turned the motor over a couple of times to have a look at the piston. On the upstroke I could see the fuel bubbling down (past the rings) but the piston itself looked incredibly clean. I then decided to take the head off to have a proper look, in case the rings had got gummed in from running too hot?</p><p>Anyhoo, both the piston and barrel are pristine, looks like there has not been any kind of combustion at all, is that normal? Like I said the chainsaw only worked the once and went through a whole tank, about 2-1/2 hours running, should I have seen some evidence that there had been combustion or not? Oh and the rings were free, not gummed at all. Gaskets in good condition and can be reused. Would it be a fuel delivery problem, over fuelling and flooding every time or some thing else?</p>
<p>I am guessing it did not start again after it cooled down, even though it may have been hot when you first tried unsuccessfully to start it. I have not had he problem you describe, but searched the Internet for related things. One person had a chainsaw that would not start much like yours. In his case the connector that grasps the top end of the spark plug had separated from the cable from the coil, but it was inside the end of the cable, not where you could see it. The lesson learned was that when things get hot they expand and sometimes things move or let go. I would not be too concerned that you cannot see signs of combustion after burning one tank of gas. </p><p>When you pull the cord several times and it does not start, take the spark plug out and see if the plug is wet or dry. That will tell you if the engine is getting fuel or not. There can also be problems with the choke and whether it comes on when it is not needed or does not come on at all (assuming it is not fully manual). </p>
Hi and thanks for the reply. <br>We had done the wet plug test before I stripped it down, yes fuel getting through OK. Now I seem to remember back in the day, I placed a piston ring in upside down in an old Suzuki 2 stroke I used to own!!!!<br>Can you install the rings upside down in a single piston chain saw or does it not matter? <br>When we took the exhaust off we could see fuel bubbling past the rings down into the barrel on the upstroke, surely this is not right and indicates loss of compression? could they (the rings) have been installed incorrectly during assembly? This puzzles me as it has been running previously. Would overheating cause the loss of compression, permanently? If there is a certain way to install the two rings it would be nice to know I am putting it back correctly. <br><br>Thank you
<p>I installed rings in a 4-cycle engine once, but that was quite a few years ago. I would look for information on the Internet about upside down installation of the rings. I have peeked through the exhaust ports on a 2-cycle engine while turning the crankshaft and did not see fuel bubbling past the piston. That would be a good thing to address. I am sorry not to be of more help. We are beyond my level of experience. </p>
Hi i have bought a two stroke scooter NOT A MOPED a scooter i road ir about 8ks and it just died i found out the fuel.i used had already been mixed before i mixed it again so double dosed the oil... i replaced spark plug , carburetor and fuel ... it starts and runs if i spray &quot;START YA BASTARD&quot; down the carbi untill that burns out then just dies again... so now i dont know wat the hell to do
What you describe sounds like fuel starvation. If you crank the engine a few times and then remove the spark plug, is there any moist gasoline on the plug? If not, fuel is not getting to the combustion chamber. Is there a filter in the fuel line or inside the fuel tank? It may be obstructed and need to be replaced. Also, if you have been burning oil rich fuel, you probably have carbon build up in the exhaust ports that will need to be removed. I described that in my Instructable. You may want to check the engine compression. To do that, remove the spark plug cable, but not the spark plug. Make certain the crankshaft can turn freely. Spin the crankshaft by hand. On the compression stroke there should be enough compression to make the piston stop and boucpnce the crankshaft backwards a little.
I have a ezogo golf cart was working then the nxt day it won't go it sits n acts like it wants to go n will then just fall on its face I've changed spark plug which has spark changed fuel filter drain gas n put new in rebuilt carb it it dosent go it will start but won't move alot
Is it 2-cycle or 4-cycle?
2 cycle
<p>Have you checked the exhaust ports to make certain they are not partially blocked with carbon?</p>
<p>I have a starting problem that has me stumped. I have replaced the spark plug, ignition coil and plug wire and fuel line. When I get the engine to start it runs great but as soon as I shut if off I have trouble getting it to start again. Any idea's?</p>
Do all of the basic checks I mentioned in this Instructable, especially that the engine and carburetor gaskets are sealing. If the engine is older than ten years, replace the gaskets, even if you need to get gas,et material and make your own. <br>When an engine is hot things heat up and expand. Hot start problems in cars are also frequently caused by fuel percolation. Too much engine heat finds its way to the carburetor and causes the fuel to boil so that the carburetor no longer works effectively. But, it may be that gaskets which were tight when the engine was cold no longer seal when the engine is hot. <br>Long before the Internet when I had an engine problem we all had to consult a troubleshooting chart in an auto manual and just work through likely causes until we found the problem. There is a good troubleshooting chart at this site. http://www.smallengineadvisor.com/members/2stroke/wont_start.html<br>
Hello I have a 43cc engine that won't start....I tried turning it over and I get nothing so I replaced the spark plug thinking it's the issue so I try cranking it again still nothing but once I took the spark plug out and tried cranking it against the frame it sparks so I know its not the ignition coil but I do see that the flywheel is rubbing against the ignition coil so I'm going to take a business card and readjust the space between the two I just don't know what to do to get a spark while the spark plug in the engine
You have done some good work already. Adjusting the magneto or coil frame so it does not scrape on the flywheel would be good, even if it is not the problem. I know you get s spark when the plug is removed and grounded to the frame of the engine. I know your engine does not start. There may be a spark when the plug is installed in the engine, but the engine would not start if the spark is not properly timed. Some engines have a soft key that shears so the flywheel does not twist the crankshaft when it stops abruptly. Very small engines usually do not have a soft key. <br>Is the ignition pointless, or does it use points and a condenser? Although probably not your problem, I once worked on a lawnmower engine that produced no spark. The primary side of the ignition coil was shorting to ground because a wire to the points was pinched. I mention that because troubleshooting these things often means laying aside all normal assumptions and proving each part of the system is still working until you find the one part that is not. <br>You have replaced the spark plug. Just for the sake of discussion, an old plug sometimes fires outside the engine, but fails to fire when under compression. <br>I know you are focusing on the ignition system. Is there any possibility the difficulty could be with one of the other systems (fuel to air mixture, clean air, adequate compression)?
<p>hi there i have a gilera sc 125 with a Yamaha dt125 engine in it and one day i was riding and my chain came off and rapped around my front sproket on my engine i pushed it to side of the road and put the chain back on started riding and my bike was fine until i go to like 20 mph and i put it on full rev and it just stayied at 20mph in every gear so i changed the clutch plates and springs put it all back together and it was exactly the same full rev clocks say 12 thou rpm and max speed was 24 mph my bike use to do 90+ no problem until my chain came off and locked around my front sprocket if anyone could help and have had this problem before please let me know thanks</p>
Hi Phil,<br>I have a 1980 Yamaha QT50 that sat in a barn for about 15 years, it was used a little before its storage but as I opened things up and began the cleaning process nothing was very dirty which was good. I rebuilt the carb, spent a good amount of time cleaning the gas tank from rust, and got it running and the mixture and idke screws are now set perfectly. My new problem is getting a consistent strong spark. I used a multimeter for about 10 hours checking every single wire to ensure nothing was shorting out as well as testing the key switch and that checked out, I replaced the spark plug coil and the cool pack, and arrived at the culprit of a faulty charging coil, it should read 295 ohms plus or minus 10% and it was at 150.. So I bought a new stator and soldered on a new charging coil and BOOM! Awesome spark every time, but now it sounds like it's misfiring because it idles great but if I rec it up nothing happens, it just remains to idle.. Any suggestions? Sorry for the lengthy explanation.
Carter, I appreciate the thorough description. It sounds like you have made a very methodical and intelligent approach to the problem. I am hardly expert on engine problems. <br><br>Do you know if this engine has a mechanical spark advance with centrifugal weights and restraining springs? The spark timing has to adjust on an engine as the speed at which it is run increases. If it does have a mechanical advance (rather than something computerized and electronic), remove the plate that covers it and see if the weights can move freely. It can happen that some corrosion sets in and the weights do not move properly, if at all, as the RPMs increase, which results in improper timing and a miss. Apply some penetrating oil and work the weights until they move freely.
Thanks Phil I will try to check that out next time I work on it, my only question is why would soldering on a new charging coil and keeping the old stator in place and everything, why would that screw up the timing? I thought the pulsar coil was for the timing and that checked out.. Oh well I'm no expert here either, I'll try it and get back to ya. Thanks again
<p>I did a search on your Yamaha QT50 and found an article at Wikipedia. It contains this interesting paragraph. </p><p>&quot;Other noteworthy features of the QT50 are its unusual charging and ignition system incorporating a six-volt battery and alternator. This system eases cold starting: when the key is placed in the &quot;start&quot; position,the ignition supplies a stronger than normal spark for initial starting, but does not allow the engine to rev so as to avoid burning the piston. Once kicked to life with the reverse-mounted, left-side kickstart lever, the key is turned to &quot;run&quot; and the engine is able to rev freely.&quot;</p><p>I do not know if you are aware of these features or not. Could anything be wrong with the ignition switch? </p>
<p>I believe I know what switch your talking about but I thought the three options were &quot;run&quot;, &quot;off&quot;, and &quot;run&quot;. Maybe the new charging coil turned that switch into a &quot;start&quot;, &quot;off&quot;, and &quot;run&quot;? I'll try it out thanks for the idea!</p>

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