FS45 puzzled at no start.

Gatafly

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Picked up an FS45 for almost nothing because it would not start and I like to tinker. Previous owner put in a new ignition because it had no spark. Still no start so he put in a new carb yet still would not start and gave up. I checked a verified spark. Also set gap on ignition as it was a little too large. Thought new carb could still be issue i tried starting with a squirt of gas in the intake and still nothing. I checked compression and it is 90. Spark arrestor is clean, new fuel lines and filter were also installed by previous owner. I think thats everything I know that's been done or checked. I'm stumped as it wont even hiccup. Any ideas out there. Thanks!
 

dfbroxy

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Check the flywheel keyway. While the cover is off clean the cooling fins on the engine. If this is a ohv engine then set the valve gaps.
 

bertsmobile1

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An FS 45 is a 2 stroke 45cc power head made by Stihl, only valves are the check valves in the carb & primer.

At 90 psi you are border line for compression on most Stihls.
pop off the muffler & check the bore & rings.
try some squirt down the plug hole with a hot plug ( 10 minutes of a hot air gun will do ).
To check the carb, remover it from the engine but leave the fuel lines attached.
Turn it sideways and blow through the carb with high volume low pressure air.
You should see the fuel being drawn through the fuel lines and also see it blowing out the carb.
 

EngineMan

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Check the flywheel keyway. While the cover is off clean the cooling fins on the engine. If this is a ohv engine then set the valve gaps.

wish people would have some knowledge before they say anything.....there are no valves or flywheel key on them...!

remove the kill wire from the coil and then try, kill switches/and bad wiring on them go bad....and you not be getting a good spark
 

Gatafly

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An FS 45 is a 2 stroke 45cc power head made by Stihl, only valves are the check valves in the carb & primer.

At 90 psi you are border line for compression on most Stihls.
pop off the muffler & check the bore & rings.
try some squirt down the plug hole with a hot plug ( 10 minutes of a hot air gun will do ).
To check the carb, remover it from the engine but leave the fuel lines attached.
Turn it sideways and blow through the carb with high volume low pressure air.
You should see the fuel being drawn through the fuel lines and also see it blowing out the carb.

wish people would have some knowledge before they say anything.....there are no valves or flywheel key on them...!

remove the kill wire from the coil and then try, kill switches/and bad wiring on them go bad....and you not be getting a good spark

I will check into these suggestions tomorrow. I always thought anything above 80 psi was try, but will loo, at the piston. Thanks you 2.
 

bertsmobile1

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I will check into these suggestions tomorrow. I always thought anything above 80 psi was try, but will loo, at the piston. Thanks you 2.

It varies from engine to engine.
Older engine will tolerate lower compressions than newer ones.
Then there are 2 ring pistons where they pump well at low compression and single ring engines where the difference between working and not can be as low a 5 psi.
In most cases you need to log the compression over the life of the mower to see when it suddenly starts to drop off signalling the need to replace the rings (s) .
I had 3 identical McCullochs from a customer all had different compressions and funny enough, the lowest compression one 65psi started & ran fine once the carb was cleaned.
The other two would not kick till they had new rings, despite both being around 90 psi.
Thus the reluctance of anyone to list a definative cut off compression.
 

Gatafly

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I checked into the suggestions and nothing. Took off the exhaust and piston and cylinder look just fine. I did notice when turn crank by hand and watching the piston that gas would bubble out the exhaust side from around the piston skirt. Not sure if this is normal or not. I did burn a bunch of residue from the muffler to clean it up a bit. I think the issue is not enough compression. I checked it again and only got 85 psi. Did some more research and seems most say anything less than 100 on a 2 stroke is likely not to start. I may try a cheap cylinder kit to see if that works.
 

bertsmobile1

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I checked into the suggestions and nothing. Took off the exhaust and piston and cylinder look just fine. I did notice when turn crank by hand and watching the piston that gas would bubble out the exhaust side from around the piston skirt. Not sure if this is normal or not. I did burn a bunch of residue from the muffler to clean it up a bit. I think the issue is not enough compression. I checked it again and only got 85 psi. Did some more research and seems most say anything less than 100 on a 2 stroke is likely not to start. I may try a cheap cylinder kit to see if that works.

Before you go throwing money at it you need a crash course in blue smoke.
I strongly recommend to go to You Tube and watch the entire 2 stroke diagnostics by Joe Pace https://www.youtube.com/user/PACEequipment.
It is a lot of work to fit new rings and / or cylinders to a chain saw.
String trimmers are fairly easy cause you have good access to to the engine.
 
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