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2-cycle engine troubleshooting

Posted by slim50 (My Page) on
Sat, Jul 17, 10 at 17:50

My 2-cycle blower cannot be started. There is a hot spark, and despite inserting fuel directly into the intake and trying starting fluid directly into the air intake I cannot get a single pop. I even took out the spark plug and sprayed starting fluid directly into the cylinder, replaced the plug and pulled but could not get a single pop.
Is it possible that the timing could be off?
What else could be the cause?

Your assistance will be appreciated.
Regards,
Slim50


Follow-Up Postings:

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RE: 2-cycle engine troubleshooting

really need to know the brand of the blower, Cheaper models wear out quicker that top of the line models?

Moving air seems to be hard on blower engines. I suspect you have no compression, especially if pulling the rope seems to be easier? First I would make sure the jug mount screws haven't worked loose (usually 3 or 4 depending on the design), also check the crank case cover screws they tend to work loose also. next I would remove the muffler and check the cylinder walls for scoring and of course a plugged up muffler (air goes in but can't get out) I rarely find this problem, but others have reported it. After all that and if you found nothing I would do an compression check (should at least be 100PSI IMO, but don't know the magic number for Two Strokes.


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RE: 2-cycle engine troubleshooting

Dear RCMoser,
Thanks for your reply.
The machine is a Sears Craftsman Model 358.797030

I did strip the machine down and checked the crankcase bolts to ensure tightness and to confirm that there was no leakage from the crankcase.
I did remove the muffler in the process. It was not clogged and looked to be remarkably clean.
I observed the piston through the exhaust port and the intake port and saw no scoring. I did not separate the cylinder head from the crankcase. All looked well.
I did remove the magneto coil, cleaned the surfaces of the coil and the flywheel. There was some greasy residue on the coil faces but not excessie. I regapped the coil to flywheel spacing to about .002 in. using clean paper. The flywheel pulls through without contact or excessive drag. I do get a hot spark.
I did not yet do a compression check but will do so if you think it is mandatory. The machine was running two weeks ago in an acceptable manner. I know of nothing that would prevent me from getting at least a pop when I try to start it. I am not getting a single pop.
Your assistance is appreciated.
Regards,
Slim50


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RE: 2-cycle engine troubleshooting

Yes I would see if you have compression! Anything less than 60 I dought it would start, but still should pop I would think??? As last resort I would remove the jug and piston (note location and disassembly so you can get the piston and crank back in on the right side (most has sprial index mark on the crank on one side or the other)(just note which side it goes in the jug.)and check clearance.(mic and telescoping gauge)


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RE: 2-cycle engine troubleshooting

Dear RC Moser,
It will take a while to proceed as you suggest. I could not locate my compression gauge right off. Will complete the test as soon as I get my hands on another one.
The remaining steps seem to be unnecessary if the compression is less that 60 as you suggest. I would think it would be time to replace the machine.
I'll report back as soon as I can complete the compression test.
Again, I appreciate your help.
Best regards,
Slim50


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RE: 2-cycle engine troubleshooting

Also remember too much fuel will kill the fire. I would suggest that when you prime, try wide-open-throttle (WOT). I also agree compression is a key element (fire/fuel/compression are the key elements) to firing and running. BUT!! With the new low compression engines, Im at a loss when I feel for compression while trying to start. With the true compression building after you start for the ease of starting, how does this affect the compression starting? I have felt very low to no compression on some 2-cycles that started and had good power. I also have some that w/n start. Ill hope to do some compression experimenting soon. Do you know of any published charts or specs on low compression or easy-spin 2-cycles? The old rule of thumb was you should not be able to hold the compression in with your thumb or finger or not less than 60 100 PSI but now who knows??

Last, make sure your compression gauge w/n make contact with your piston. loger


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RE: 2-cycle engine troubleshooting

Dear Loger,
Thanks for your reply. I still have not yet obtained a compression gauge. I did try what you suggested. I removed the plug, inserted my little finger in the hole, then pulled the cord. I could not feel high compression. My finger was not blown out of the hole. I did feel slight compression.
I am still at a loss why I cannot get even a pop when I have hot spark and use starting fluid(ether).
Best regards,
Slim50

Here is a link that might be useful: GardenWeb


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RE: 2-cycle engine troubleshooting

Slim : You certainly have compression issues from what you have indicated. You should also feel a slight suction on the intake stroke . You may also have a base gasket or crank seal issue compounding base compression. Only a Valid Compresion Test will validate this condition .
Loger: I think you are referring to Decompression Release Devices on certain Models only , which assist in ease of start up .


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RE: 2-cycle engine troubleshooting

Ewalk,

Please explain how the Decompression Release Devices work. I related the Easy Spin seen on some mowers with lower compression. Actually it could refer to gear ratio also. I really do not keep up as much as the past on the small combustion engine technology vs as needed now. With Decompression Release Devices technology, will you still get a fair compression reading?

In my early 70s automotive days, I feel I had a cylinder to fire while I was trying to hold a compression gauge in a hot engine. My ears seem like they are still ringing now (and they are from a log splitter possibly) and the gage showed about 300 PSI. That influenced me to use the slower better screw in gauges.

Do you have any hydraulic log splitter experience as to them being noisy and ways to make them quieter? Logger


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RE: 2-cycle engine troubleshooting

Loger: My experience within the Decompression Device relates to Chainsaws and Old Motor Cycles (Single Cylinder) where High Compression made it difficult and in some cases Dangerous (kick back )to Pull over or Kick over the Equipment. A simple Plunger Style Poppet Valve Device was utilized to allow escape of some of the Cylinder Compression from within the Cylinder Head during Start up . It was manually activated by a small (normally) lever or cable usage. I have heard of the same with some larger engined ATV and LT Units with Manual Recoil Starting Requirements , although with the advent of electric start on most newer Recreational equipment decompression is no longer a issue .
I believe I have already answered your Hydraulic Log Splitter question within another thread , check it out .


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RE: 2-cycle engine troubleshooting

Message for all who were concerned that compression would be the core problem.
Well, a compression test was run with a first class compression gauge and the results are as follows:
With two pulls the reading was 75 psi. This was verified several times.
I would imagine that the reading would be a bit higher if I had put a shot of 30 wt oil in the cylinder before running the test. For the readings obtained the cylinder was essentially dry, that is, no fuel mixture was in the cylinder before the test was started.
It is still a mystery why I cannot get even a pop out of this engine.
Any other ideas??
Best regards,
Slim50

Here is a link that might be useful: GardenWeb


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RE: 2-cycle engine troubleshooting

If you have prime and pulling before, there should be mix inside the crankcase. Usually there should be a thin coat of oil on the rings and piston and that should give you some seal. Try put a drop of oil in and do the compression test again. 75lbs is not low to the point that the engine is dead.

There is not timming in 2 cycles.

If you remove the plug and pull the cord, do you feel air coming out of the plug hole? You should if you have good seal on the crankcase. And you should smell gas after a feel pulls. If you, you might not be getting gas. Check pulling the cord without the spark plug and observe whether puff of air come out, and smell the gas after 7 or 8 pulls. If not, hold the throttle open and pull a few more times. If you still don't smell gas, you are not getting gas from the carb.


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RE: 2-cycle engine troubleshooting

Yungman: He has verified spark and primed the engine previously via the spark plug and carb venturi with Starter Fluid. Slim: If as stated ran the mower within the last 2 weeks residual Oil will be retained within the cylinder to ensure proper sealing of the rings.

Note : At least 4-5 pulls required to accurately measure compression . 75 # is marginal compression . I would think you may get higher readings with additional pulls.
You are sure you have a nice Bright Blue Spark ? You may have to add a dribble of fuel mixture within the plug hole and retry not to much to cause a Hydro lock situation .


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RE: 2-cycle engine troubleshooting

Loger: Did you find the July 15th Hydraulic Log Splitter response ?


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RE: 2-cycle engine troubleshooting

ewalk,

Thanks for the follow-up. I did get the good info and remembered the splitter working to good to have any of the related problems. I'll keep the plugs in and muffs on for the short times I use it. The splitter and my chainsaws might let me work with firewood a few more years. I wish I had gotten the splitter in the late 70s vs now. The shock and work from splitting wood is showing in my hands, arms and back. Cutting my personal firewood is what got me into 2-cycles (servicing and rebuilding mid size Poulans). Two have averaged 4 cords per year since 1978. I have serviced too many of all brands for friends since the mid 1970s.

I have gotten on too many message board and into to many conversations to keep up (4). Good Money Saving Info!

loger


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RE: 2-cycle engine troubleshooting

Loger: I hear you , recently hand a Hip Replacement and do on occasion feel the ache in the knuckles on damp days . Signs of a misspent youth lol . I wouldn't have done a thing different , oh perhaps quit playing Competitive Hockey a few yrs earlier may have Prolonged the Joint Replacement Requirement :) Have fun with the Splitter Dude !


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RE: 2-cycle engine troubleshooting

I don't like using starting fluid for priming. it evaporates too quickly and has no lubication qualities. Carb. cleaner is a much better choice IMO. It don't evaporate very quick, hard to flood an engine unless you just keep spraying, and has some lubrication properties. Plus it don't hurt the engine to run off carb. cleaner, Now I didn't say fill the gas tank up with carb. cleaner and go weedeating cause heat will build up after few minutes and lock it up due to the load being put on the engine.

I have alway used carb. cleaner for priming. First I remove the plug, squirt about two second blast into the cylinder head. Pull the rope blow out any excess. Then I wet the plug with carb. cleaner ( this does two things, Cleans out any over oily parts from flooded engine and primes the comb chamber for starting) When I do this I alway get it to fire off the first or second pull no matter how long the set or how flooded they may of been.

After it fires and dies then I spuirt a one or two second blast down the carb. and pull the rope. this usually takes two to 4 pulls for it to fire and run till the carb. cleaner is used up. Now I know I got a fuel supply problem.

In your case if it don't fire or pop with this method then IMO you either have little compression (due to worn out jug and piston clearances or a massive vaccum leak) I think you have already explained you are getting fire! pretty blue spark right??


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RE: 2-cycle engine troubleshooting

RC: I agree with the evaporation point but the lubricity concern is really not all that important on a 2-Stroke application for this testing application there is more than ample lubrication within the cylinder . The validation of any viable compression and crankcase vacuum with the ether volatile mixture was what would identify any ignitable fuel mixture. Failing this Properly Mixed fuel dribbled slightly directly within the combustion chamber was the next best approach. Until he attempts this and actually conducts a valid 4-5 pull compression test he still is reaching . I think our conclusion of poor compression and vacuum along with possible weak spark are probable causes for lack of
ignition of any accumulative fuel . Slim has not yet confirmed my previous question of Bright Blue Spark only his assertion of "Hot Spark" which can be deceiving lol .


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RE: 2-cycle engine troubleshooting

Repost-1st one didn't make it for some reason.

1. A bit of a stretch, but you might want to try a new plug. Plugs have been known to fire under ambient pressure, but not under working pressure. May be worth a try and not really a waste......i.e., a spare plug on hand ain't a bad idea.

2. Another stretch.....if there is a way, you might check for "fire" with the plug wire bent into its installed position...just in the event it is cracked or broken inside.

Agree with all though......there should at least be a "pop"


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RE: 2-cycle engine troubleshooting

Youracman: Very sound points to consider , never a stretch or stupid question when it comes to trouble shooting Bro !


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RE: 2-cycle engine troubleshooting

Dear All,
I know it may be confusing and jy explanations may be somewhat lacking and for th;is I apologize.
To verify hot spark I have removed the plug, grounded the base with a wire to engine ground, and the spark plug cap in place on the top. The spark observed is hot blue. I did not try to measure the strength of the spark of measure the maximum gap that could be obtained. What is observed is a spark that should certainly fire fuel in the cylinder.
I have inserted fuel directly into the cylinder via a removed spark plug, then reinserted the plug and pulled and got not a single pop. I have done likewise with starting fluid. Not a single pop. I have inserted fuel into the carbutetor in sufficient quantity that I am convinced it reachtd the combustion chamber because I pulled the plug and found it slightly wet with fuel.
With all of this and not a single pop I am am inclined th think that it has to be timing. With fuel and spart there has to be at least a pop. Now, why tliming might be off I have no idea. The flywheel is keyed to the shaft and that has not changed.
It all still remains a complete mystery to me.
Thanks to all for their help.
Best regards,,
Slim50


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RE: 2-cycle engine troubleshooting

I have two 2-cycle engine questions if someone's interested.
1 - String Trimmer - Rough Starter but once it starts it stays idling. But, when I give it gas, it dogs and dies. There's only one adjustment screw and that's for idle speed. Any ideas what I need to to do remedy this problem?
2 - My Mantis and snow blower use 50:1 ratio. The trimmer uses 40:1 ratio. What's the diff (besides 10 points)? Can I use one ratio interchangeably for all tools?
Thanks!


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RE: 2-cycle engine troubleshooting

Hor: What brand is the trimmer ? Sounds like fuel restriction issues . Normally adjusting the Low Speed Jet would resolve the stumbling (hesitation) issues. Try some concentrated Fuel cleaner (2 ounces) within fresh fuel . Let the unit idle until warm before attempting to increase rpm this will allow the cleaner to begin to work . Go with 50:1 Ratio accross the board just ensure a Premium Syn Oil of your preference . I love Amsoil Sabre . Keep in touch Bro !


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RE: 2-cycle engine troubleshooting

"There is not timming in 2 cycles."

Huh?

Presumably he meant timing. Timing is critical with any internal combustion engine. It wouldn't hurt to pull the magneto flywheel off to make sure the woodruff key is intact. When that key shears timing accuracy is lost.

That would also allow inspection of the magneto end crankshaft seal. In a 2-stroke engine crankcase compression that forces the fuel-air mix through the transfer ports to the combustion chamber on the piston's down stroke depends on leak free crankshaft seals. Those seals are inexpensive and easy to replace.


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RE: 2-cycle engine troubleshooting

R&L: Is there a valid reason that you feel compelled to post a response to Yungman after over 10 mths ?


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RE: 2-cycle engine troubleshooting

ewalk, I didn't notice the age of the issue. My mistake. Even so, the thing may still not run and the cause may be a sheared mag woodruff key. That's actually happened to me on a B & S powered camping generator I made using a car alternator about 30 years ago. In that case my experience may be useful.

In general, I find these forums very interesting for 2 reasons. First, there is always something to be learned from people more skilled and knowledgable than myself. I have learned a great deal from technical publications and the occasional true experts who post to various forums.

Second, the various amateur opinions can be really amusing and fun to read. An never ending example is "My Husky/Stihl can beat up your Stihl/Husky". In 11 years of reading this forum the longetivity of that topic really amazes me.

Again, I made a mistake in not noticing the age of the issue. In my self defense, it is way up on the page so seemed "current".

Ray


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RE: 2-cycle engine troubleshooting

No Harm done Dude . Just had to ask the question , some of the older forum members get a little tired of old articles be dragged back to the forfront for no actual benefit . These articles are for reference only . I personally would prefer people to start a new thread when req'd .It always amazes me when people have the ask the same questions that have been answered 100 + times but just have to ask it again , as if the answer is going to change lol . I agree with your Chainsaw Philosphy . I just wish people would read previous threads with pertinent info and refrain from duplicating questions and answers :)


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RE: 2-cycle engine troubleshooting

Ewalk, the information on this forum can be very useful. For example I just bought a Poulin pole saw from Northern Tool. It is obviously not a quality item but a really good pole saw from Stihl or Husky would cost 3 or 4 times as much and mine will be used only on my property. The trees here are mostly mature oaks so once they are limbed up the pole saw will be in mothballs.

Upon opening it I noticed that unlike my saw (Stihl 026) and string trimmer (Echo) that both came with fixed jet carbs that I had to retrofit with adjustable carbs, the pole saw has an adjustable carb. The adjusting screws are splined rather than slotted to prevent owner adjustment

Following up on information in this forum I found an ebay seller in Florida who has the tool for the splined screws. As you know, lean running is death for 2-stroke engines so now I can adjust the carb to run properly.

Another 2-stroke issue I find very interesting is premix oil ratio. My initial interest in that subject was because I was an off road motorcycle racer and that form of racing is a true test of 2-stroke engine durability. Objective dynomometer testing of race engines with various premix oil ratios was very enlightening to me. The test results completely contradict the recommendations in 2-stroke owners manuals. From that I conclude that the 2-stroke engine manufacturers are saying what the emissions bureaucrats are telling them to say, not what they know is best for engine performance and longevity.


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RE: 2-cycle engine troubleshooting

R&L : Yes , Splined , D , Pac Man Styles are the most common adjusters currently . Quite often I just suggest using a dremel to slot the heads unless the owner routinely does small engine carburator repairs. As for the 2-Stroke Oil debate I agree 100% . Having Raced Motocross and Enduro along with Semi Professional Snowmobiles (Sno-Pro) I always used plug check colouration to determine proper engine performance and tuning . Back in the day it was routine to re-ring and parallel hone cylinders every 3-4th Race . Decarbonizing was also normal requirement with Castor Based Racing oils back then . It's like night & day with the Superior oil technology of today as you well know lol . But there was something wild about the smell of a well tuned 2-stroke running Klotz "R" with AV 100LL . I pretty well run Amsoil Sabre now within all my 2-Strokes from 50:1 to 80:1 ratio depending on the application . I use to laugh at the local Dealer's advising customers to run 24:1 or 32:1 ratios back in the 70's when 40:1 was more than adeqaute even within Racing extremes. Hell we may even of competed against each other if you ever raced within the Mid-West , but probably not since I a little long in the tooth lol . Thanks for the Memories Dude ! :<) .


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RE: 2-cycle engine troubleshooting

When there is no compression, I always think its the rings or head gasket. What about the reed valves?


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RE: 2-cycle engine troubleshooting

A worn-out piston ring with an excessive ring end-gap will cause a no-start issue big time with these small 2-strokes. Racers prefer a real close gap, but .012" is considered sufficient for compression on a trimmer or blower. I think 90+ PSI is the neighborhood you want your compression rating in for normal starting.


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RE: 2-cycle engine troubleshooting

I have a Poulan Wild Thing 18" chain saw that kicks back when trying to start. I checked the fly wheel key and it's OK. Any idea ?


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RE: 2-cycle engine troubleshooting

Is it violent as pulling the string out of your hand? Otherwise, it could be a good compression stroke.

Any history on the saw’s past performance compared to the present? IMO, a carbon build-up from rich oil mix or bad plug fire might affect the compression stroke. Pulling the muffler should give you a glance onto the top of the piston X carbon build-up. There is probably a chemical to run if there is a carbon build-up.

Please share your find or cure.


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RE: 2-cycle engine troubleshooting

Thanks for thr info . Kick back is violent . I will check your suggestons and let you know what I find.


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RE: 2-cycle engine troubleshooting

jimdean59, I ran a search on troubleshooting Poulan Wild Thing 18" chain saw and saw lots of potential info at the 1st page. The page address is below and a youtub on the page address is below. The quality of the youtube was not good but compression release was mentioned. I wonder if your compression release is not working and if it would feel as a violent kick back??

Hopefully the big and new saws experienced users will Jump in and share. I have learned that I have little to no experience on saws above the 70s or large saws with compression release systems. But! My Old School Basics 2-Cycle Basics Still Goes A Long Ways.

http://www.youtube.com/watch?v=jei9xQw5IzA

Here is a link that might be useful: troubleshooting Poulan Wild Thing 18


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