Stihl ms180 won’t start

[DerekE]

Stihl ms180 won’t start up at all, doesn’t even pretend to start … I’ve tried all the obvious stuff

- has good spark and fully cleaned spark plug
- has good compression measured at around 165psi
- piston looks great, no scoring of any kind
- totally cleaned the carb. Tried with brand new carburetor just to be sure…
- brand new 50:1 stihl mix gas in the tank
- fuel line looks fine and is feeding gas, carb is soaked after attempting to start from full choke position.

I am stumped and hoping someone may have an idea of what else to try before I just buy a new saw…

 

[Bob Hedgecutter]

Okay- all we need for a 2 stroke single cylinder engine to run is- correct air/fuel mix entering the combustion chamber, it being compressed and a spark to ignite it.
Pretty simple mechanics- till it isnt.
We also need timing of the spark occurring at the correct part of the compression stroke- sheared flywheel key is the usual cause of goofed up timing- but not if the flywheel is still factory tight and has not been removed and replaced recently.
Next up is a massive air leak- like main crank seals and or a loose engine pan on a clamshell engine like the MS180 has- enough air getting sucked in around and below the piston- pushed up through the transfers with the deemed to be correct explosive charge leans things out enough that it wont ignite.

If indeed all else is correct- willing to bet air leak is causing your woes.

Now, if all else is not correct and this is a "new to you" saw you got off marketplace and the seller said it was running last time they used it, then you are likely to be in for a bigger repair bill than the thing is worth- so some kind of background story be nice.
Is it new to you?
Did it run and then scream, then die and not restart?
Did it chug slowly to a stop and refuse to restart?
Was it stored for a few years and you decided to get it going again?

 

[DerekE]

Great info, thank you. I’ve had the saw for a few years, sitting in storage for probably 2 winters now. It worked ok but not great before that (lots of smoke coming off the chain, maybe not lubricated or cleaned well enough).

Would I get good compression with an air leak?

 

[Bob Hedgecutter]

Yes you will get compression with an air leak- as long as the leak has not leaned it out enough to burn up the piston and destroy the rings- the vapor still compresses as it is above the transfers- just the fuel to air ratio is way off so it doesnt go bang.

Stored for a couple of Winters, fuel delivery might still be an issue.
If you had been trying to start it with many rope pulls, saw should just about flood to the point raw fuel is coming out of the muffler.

Because that is another option- nothing wrong in so much as you simply flooded the saw and too much fuel is over riding the air volume- that wont go bang either.