Stihl 46S

Nickster2213

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I am having a very difficult time starting Stihl 46S grass trimmer. This was given to me to see if I could get it to start. I have rebuild the carburetor and also replaced it with a new one, new gas line,filter, air filter, sparkplug, fresh gas and compression is 148 psi. I can get to start and run nice if I use quick start or a little gas in the cylinder. That is the only way to get it to start. Ready to toss it to the curb.
 

StarTech

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As far as I know there is no 46S string trimmers. Is it a FS46?

IF so have check the muffler's spark arrester for clogging with carbon?
 

Nickster2213

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Yes I did clean that also and I did a bench test on the coil. All seems to be good, it takes quite a few pulls to get it going.
 

StarTech

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The only to test the coil other than very factory tester is with the coil mounted on the engine with the flywheel magnets flying pass it. NO ohm meter tests as it is impossible to the electronics via an ohm meter.

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bertsmobile1

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Two strokes require both crankcase compression as well as cylinder compression
Crank case compression is controlled by the seals at each end .
You test them in both pressure & vacuum
One of the signs of worm seals is engines that are very hard to start cold but start fine during use
Or start very hard on Friday afternoon, work perfectly all weekend but be impossible to start next Friday when the seals have dried out again.
Joe Pace did a series of 2 stroke diagnostic techniques and this is the one on Crank Case Testing
It takes about 1/4 to 1/2 hour to do if you have all of the gear on hand .
If some one comes in and asks me to test their trimmer I charge 1/2 hour same for a blower and 1 hour for a chainsaw .
The time eater is making the kit to do the tests with
 

Nickster2213

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Just finished doing a pressure and vacuum test on the unit and all is good with it, no leaks. Let it sit over night under pressure and did the same with vacuum all test held. I even put the whole thing in water to see if and bubbles showed, and did the soap spray and no bubbles.
 

bertsmobile1

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Well this is both good & bad
If the tests were done properly ( piston at BDC ) then that only leaves the replacement carb and If it came from Ammozone or Evilpay and in particular if it came with a kit ( air filter, fuel filter, spark plug & tubes ) then there is a 90% chance it is defective .
And in particular the choke is not closing fully
I am not familiar with this model
If the choke is on the air filter then you have a leak between the air filter housing & the carb.
Apart from allowing fine dust into the engine a leak there will have no effect apart from making the trimmer hard to start
 

Nickster2213

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Ok, thankyou, I did do a rebuild of the original carb also and still it takes many pulls to get it going. I do believe I am the second person that tryed to get this to start properly.
 

bertsmobile1

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People rarely change the air filter to carb gasket .
The gasket is soft to conform & make a complete seal
They take on a set over time so when replaced they can not compress any more so fail to make a proper seal .
 

Nickster2213

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Yes did that also, I make all my own gaskets for all my small engines. Good quality gasket material.
 
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