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Ironhead

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I have a Stihl ms251 saw that won’t start. I have replace ignition and the spark plug and still no spark. Please help. Thanks
 

SE#1

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I have a Stihl ms251 saw that won’t start. I have replace ignition and the spark plug and still no spark. Please help. Thanks
What is the air gap that you used?
 
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Czed

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How's the compression?
 

Ironhead

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Used a business card
 

SE#1

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Unhook the ground wire and then try to start. Look for spark with the ground wire disconnected. If it starts, it will not shut off because ground wire is disconnected. Enable choke to kill it.

Based on the information you provided, it appears the ground wire has a short or the on/off switch has an issue. Usually, the ground wire rubs bare and then shorts on the engine. Hence, no spark Boss....

While you are there check magnets on flywheel, make sure they still have magnetism.... 🧲
 
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bertfixessome

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Good is not a response to that question
XYZpsi is the reply we need
The difference between starts and will not start can be as fine as 10 psi which I found out the hard way after spending way too many hours trying to get a concrete saw to run
On my tester anything less than 150psi is a waste of time
I think that figure is fairly accurate as it has a solid pressure tube
Most car compression testers will give a low reading and on top of that a long rubber hose can take near 100 pulls to pressurize when you are only pumping in 20 to 40 cc
 

Ford3000

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Is there a spark at the plug.
Did the flywheel key shear and throw the timing off.
Try some fuel down the plug hole and see if there is
a kick of some sorts.

When did the saw last run, did it die and refuse to start,
has the saw lay up for a period with fuel in it, have you
tried replacing the fuel with new fuel.

Have you looked at the fuel filter to see if it is clogged,
how about the fuel lines, the vacuum line, is it on off
or cracked, same with fuel lines, are all the linkages on
the carb connected up.
 
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