I am trying to fix a Stihl FS 55R lawn trimmer would not keep running when cranked. I checked the fire through the spark plug and found it firing. Checked the compression and got 100+ and pulled and cleaned the carburetor. It still would not keep running. I then REPLACED the carb with one from China that I found on Ebay. How do I adjust the high and low jets for starting? I have pulled the crank mechanism off and am trying to start by cranking with an electric drill and am using Starting Fluid. Engine will run maybe two - three seconds and then dies after apparently running out of fumes of starting fluid. I screwed the high/low adjustment screws all the way in and then backed them out 1 turn and then tried 1-/1/2 turns and then 2 turns and still will not keep running. Because I'm holding the throttle wide open the engine revs up then dies. IMHO the carb is apparently not allowing the gas to flow. I am beginning to wonder if the trimmer has been run using fuel not mixed with oil. I am also concerned that maybe I may be damaging the engine using starting fluid. I do not know the symptoms of an engine being run with non-oil mixed fuel. What else could be the problem?
Oiless fuel ruins your compression. The trimmer should crank anywhere above 50 psi. A good place to start with the jets is 3/4 to 1 out. You may have damaged the new jets by srewing them all the way in. These small jets are often needle thin and can be damaged when bottomed out.
SOURCE: Snapper SS312 weed eater. Cranks when primed but won't run
I am sorry to say this, but the compression for that type of engine should be atleast 120 psi. Remove the muffler and look at the cylinder, it is scarred beyond repair.
SOURCE: Engine will only run on 1/2 Choke
Hello edv40026:
Have you Checked the Exhaust Port and Muffler for Restriction?
From your Description it Sounds like the Exhaust Port or Muffler is Restricted with Carbon Deposits, the Carburetor Metering Pump Actuator Gap is Incorrect or the Compression is Low (Worn Rings/Cylinder).
>>The Following is a Basic Instruction File for Doing a Diagnostic on the Engine for this Problem. Any Input is Appreciated.
>>**Remove the Muffler and Make Sure the Exhaust Port is Clear.
>>If it is, then Try to Start the engine with the Muffler Off.
>>If it Starts and Runs Properly, then Clean the Spark Arrestor Screen in the Muffler or Replace the Muffler if Required.
>>The Following is a Basic Instruction File for Doing a Diagnostic on the Engine for this Problem. Any Input is Appreciated.
>>**Remove the Muffler and Make Sure the Exhaust Port is Clear.
>>If it is, then Try to Start the engine with the Muffler Off.
>>If it Starts and Runs Properly, then Clean the Spark Arrestor Screen in the Muffler or Replace the Muffler if Required.
Is the Fuel Line from the Fuel Filter Staying Full of Fuel?
The Carburetor Metering Jet Actuator is Set so the Pump Diaphram Dowl is Just Touching the Actuator Arm. These Components are Located Under the Cover with 4 Small Screws Holdong it to the Carburetor Body.
Please, Do Not Hesitate, If you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.
Good Luck
Respectfully
jbridger (John)
Hi jim gabriel
Sounds like you have dirt/debris in your caburetor jets,fuel passages
Check/Clean/Replace your Air Filter, a dirty air filter can make your engine run to rich with fuel.
Note: ALWAYS USE COMPRESSED AIR TO CLEAN YOUR JETS AND PASSAGES, VERY IMPORTANT.
Note:Before you disassemble the carburetor:
Write down on a piece of paper or take a picture of how the linkage attaches to your carburetor for later reference when you go to reinstall your carburetor.
Mark each piece with a awl, or some kind of instrument that will make an alignment scratch before you disassemble the carburetor into separate pieces.
That way you will know which way it goes back together when you reassemble it.
Sometimes you can get by with priming the carburetor or by using a very small shot of starting fluid and letting it run a few times like that, and it will flush the gunk out of the jets,but most of the time you will need to rebuild the carburetor.
Be sure to check your fuel tank for water and dirt/debris, if there is water/debris then you need to clean your tank.
Check you fuel line condition after a while they will degrade and need replacment.
Check/Clean/Replace your fuel filter if you have one, normally they are located in the fuel tank of chainsaws and weedeaters.
When you remove your fuel lines from the carburetor be sure to make a drawing to how the lines are connected to the carburetor or take a pictue for later reference.
Normally the big line will be the line the fuel filter is connected to inside of the tank.The smaller of the two lines is the return to the fuel tank from the carburetor after it is pumped thru the carburetor by the primer bulb.
Make sure you are using fresh fuel...and oil if your using a two cycle chainsaw or weedeater with the oil to the right mixture...too much oil as it can cause hard starting and excessive smoking.
If the chainsaw/trimmer is over a couple of years old, then I recommend that you buy and install a new carburetor repair kit,because the diaphragm will get hard and that will cause it to be hard to crank.
The diaphgram may look good and flexible, but it can be deceiving and not act as a fuel pump as it should because it has become too hard and will cause hard starting,start and run and shut off, etc.
When you clean your carburetor, I recommend that you use a laquer thinner type cleaner to clean and dissolve the laquer build-up in the float and needle jet passages.
Be sure to remove all plastic and rubber parts before using the laquer thinner because it can dissolve the plastic parts and render them unuseable.
Be sure to use COMPRESSED AIR to blow out all the fuel and air passages.The higher air pressure is needed to blow some of the trash/debris from the fuel or air passages.
Be careful when blowing out the passages, because there are sometimes small rubber type seats in the bottom of some of the passages.
Keep in mind that the float (if you have one) for the carburetor must be level when you go to reassemble the carburetor or follow the instructions you get with the carburetor kit, or you could also ask the parts man that you get your kit from.
When you clean your carburetor and remove the jet screws, you will first need to lightly seat the jet screws.
But before you lightly seat the jet screws count the number of turns it takes to seat the jet screws from their original position.
Be sure to mark the turns down on a piece of paper.
That way when you put the jets back in, you know to lightly seat them first and then turn them back out to their original position before you started.
Note:
The little spring inside of the carburetor goes under the float arm.
That is where your fuel inlet needle/float valve is located...on the arm at the end.
Normally there is a small indention in the carburetor base and a small protrusion on the underneath of the float arm where the spring will be in the right postion for installation.
The spring will set in the indention and you will install the float arm with the needle/float valve and float rod into position over top of the spring,you will push down until it is in position and then you can tighten the screw that holds the float arm assembly in position.
Once you have your carburetor cleaned/rebuilt that should solve your problem.
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Bud
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