# I can get my stihl weedeater started



## small engine (Oct 14, 2010)

I have a stihl f5 55 rc weedeater. when i try to start it it just fires but wont even run for a sec, it will fire with every pull but thats the most i get, ive tryed to adjust the jets, i checked the timing, ive change the spark plugs, the muffler isnt clogged, im lost and dont know what else to try, any info or what you think let me know thanks


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## justin3 (Apr 10, 2007)

Did you check the cylinder for scoring or do a compression test?


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## small engine (Oct 14, 2010)

Yes their is no scoring, it lookes brand new, its got good compression


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## geogrubb (Jul 28, 2006)

I had one like that, only 1 pop per pull, never 2 or three, but can't remember exactly what I did, I think I removed the plug and cranked it about 20 times to clear the engine. It's worth a try. Have a good one. Geo


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## Rentahusband (Aug 25, 2008)

Sounds like it is not getting proper fuel. Have you cleaned/overhauled the carb?


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## small engine (Oct 14, 2010)

yes i have cleaned the carb, its getting enough fuel but dosent keep running


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## luckyvision (May 24, 2007)

first, did you pull the screen from the muffler? they clogg with carbon (use a low ash oil)

you can't clean the carb with carb cleaner, it'll warp the mylar check valves, which are not servicable. use brake or electronics spray.

sounds like the low speed check valve may be stuck. sonic cleaning may help, but if you cleaned it once, probably not.

a replacement carb ranges from 40-60. worth the $ if the cyl isn't scored.
--Lucky


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## small engine (Oct 14, 2010)

Ok My sister has the same weedeater so when i had to watch her kids for her i switched the carb from hers over to mine and it did the same , thing, i have taken the muffler off and the screen wasent clogged, ive changed the spark plug , checked the timing i am lost now i thought it was the carb but it isnt


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## usmcgrunt (Sep 16, 2007)

Since you have good spark and a known good carb,have you actually done a compression test?Even though you said the piston wasn't scarred,you could have a stuck piston ring or the bolts holding the cylinder and block together are loose and sucking air.The engine has to have good compression and the ability to create a vacuum for it to run correctly.Hope this helps.


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## small engine (Oct 14, 2010)

I know that the rings arnt stuck and they are in good shape bec i had it all the way apart to repack the bearings, but when i get home tommorow i will check the compression with my gauge, even though it seems to have good compression thanks


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## usmcgrunt (Sep 16, 2007)

I'm confused now.Why was it taken apart originally and what bearings would have to be repacked?All the engine internals would be lubricated by the fuel/oil mix.Could you have possibly damaged one of the seals on the bearings and now have a crankcase leak?


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## small engine (Oct 14, 2010)

Ok Ill tell you why and what i did. I noticed it was hard to turn over, and it would only just fire and not start so i took it all of the way apart and the bearings had like bread crumbs kindof stuff and were hard to turn so i took them off the crank and oiled and repacked them and put it back together and it did the same thing, i didnt damage any of the seals, its still doing the same thing before i took it apart, I packed the bearings because i thought maby it wont run bec the bearings were hard to turn over, but everything is moving good now and i just have to figure out why it wont run im going to go out to my shop and do a compression gauge and ill let you know thanks


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## small engine (Oct 14, 2010)

Ok i did a compression test and its about 85 psi


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## usmcgrunt (Sep 16, 2007)

85 PSI is actually on the low side for two cycle motors and will make it harder to start.You have to have good compression,fuel and spark at the correct time before it will run.You said it has spark,you tried a known good carb and it still won't run.It was mentioned before,but,it sounds like a stuck piston ring or a damaged cylinder.Have you tried squirting a little premix fuel down the spark plug hole and starting it? The gas has to be fresh and clean.Is the flywheel key sheared and throwing the ignition timing off a little?


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## small engine (Oct 14, 2010)

like i stated before the rings arnt stuck and the key is in the right place, ive seen lots of weedeaters and most are running about 75 psi and the 4 stroke engines on mowers are running 125 to 175 i dont think its a compression issue


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## chuck_thehammer (Oct 24, 2007)

a question...you said in another post of repacking the bearings..what do you mean??

you have spark...outside of engine....but the real question is do you have spark under 90psi and fuel and air and oil mix...plus the 14 psi the air puts on all of us.
it is not easy to test under full preasure. inline spark tester, if you can find one.
replace everything in the spark system...

the engine should run if you spray starter fluid in the carb and run for 5 to 10 seconds...it will even run without a carb attacked to the engine..

try it...sounds dumb...put it does work. if it will not run than something is bad, like coil or coil wire. plug cap. plug. or something is killing the coil as it tries to spark..


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## small engine (Oct 14, 2010)

ill unhook the wires to the coil and see if it starts, bec that would eleminate anything to do with the wiring


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## small engine (Oct 14, 2010)

i took it apart and unhooked the wires and it still does it so I am lost, it has compression, spark and fuel and right timing and it wont start,


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## usmcgrunt (Sep 16, 2007)

Hmmmm! Starting to run out of ideas!Are you sure the seal between the cylinder and crankcase is good?Is the choke working properly?Is the air filter clean?Did you try a little premix down the spark plug hole to start it?The last resort would be a leak down test to see if one of the seals is leaking and sucking air.Most people don't have this tester and the necessary block off plates.As long as you keep asking,we'll keep trying to give answers.I know I have said it before,but the low compression is still a concern to me.


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## ladornato (Jul 31, 2011)

Seems like I had one that was doing that. I believe I had the fuel lines to the carb. reversed. It has been a while but seems like that is what it was.


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## jsouth (Jan 31, 2008)

The compression is way to low for a stihl trimmer.My 2 cycle service manual says the compression should be above 90# or better to run.Go and get your sister trimmer and do a compression check,I bet it will be 120# for better. Hope this helps.

Jerry


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## small engine (Oct 14, 2010)

I ordered new piston rings and they should be in tomorrow, so i will let everyone know what happens i hope this fixes the problem


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## jsouth (Jan 31, 2008)

Your stihl trimmer has to low compression.My service manual,says compression should be 90# or better to run.Go and get your sister trimmer and do a compression check.I bet it will be 120# or better.Hope this helps.

Jerry


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## jsouth (Jan 31, 2008)

Sorry about the 2 post.

Jerry


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## small engine (Oct 14, 2010)

Bad News i got the new rings and got it back together and it still does the same thing.


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## usmcgrunt (Sep 16, 2007)

Did you do another compression check WITH the new rings?If the readings improved a lot,we need to go in another direction.If the readings are still low,there must be scarring or a crack in the cylinder that is preventing higher compression which is absolutely necessary.


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## small engine (Oct 14, 2010)

ok i will do the test a little later thanks


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## small engine (Oct 14, 2010)

The compression is about the same, their is no scoring in the cylinder


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## small engine (Oct 14, 2010)

I tested the compression on my sisters weedeater, and it was about 75 to 85 lbs. Which was the same as the weedeater im having trouble with, my sisters weedeater runs great and is easy to start so the compression isnt the issue here


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## justin3 (Apr 10, 2007)

I tested two FS55's we had in at work for service, they both had 110-120psi, something is wrong with your gauge or you have low compression. Are you holding the Throttle wide open?


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## small engine (Oct 14, 2010)

no im not holding the throttle wide open, even if my gauge is worng , since the other stihl i have has about the same compression and it runs great that rules out the compression problem


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## justin3 (Apr 10, 2007)

Stihl chart says at least 90-95psi to run.. Something sure is fishy here. If compression truly isn't the issue, Are you positive the Crankcase seals and Cylinder gasket are in good condition? No part of the muffler is clogged? have you tried running it without the muffler?


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## small engine (Oct 14, 2010)

No i have not tryed to run it without the muffler, i didnt look clogged, i am pretty sure the seals where good, i used rtv to seal the bottom, thats what was their when i took it apart


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## justin3 (Apr 10, 2007)

Sounds like you have an air leak somewhere in the crankcase, cylinder head, crankshaft seals or where you applied silicone.


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## jsouth (Jan 31, 2008)

The compression is to low for that trimmer.My service manual says the compression should be 90# are better to run.The stihl trimmer you have should be at least 120# compression.Go and do a compression check,on your sister trimmer,and see what you get.Hope this helps.

Jerry


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## justin3 (Apr 10, 2007)

He did check his sister's unit, he said the compression was 75-85psi Something doesn't add up because my service manual also says 90psi of compression before it will even run, I tested 2 FS55's I had in for service and they have 120-130psi


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## small engine (Oct 14, 2010)

i guess my gauge is worng but its still the same as my sisters that runs


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## small engine (Oct 14, 2010)

Well i just am parting the weedeater out but thanks for everyones help


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