Chainsaw won’t start – basic troubleshooting advice

[rworkman98]

My chainsaw stopped running yesterday.  It’s failed before, and I’ve fixed it before (tune at idle, fuel line replacement).  But this time I’m at a loss.  

My first guess was a problem with the carburetor or the fuel line.  However, I took off the carb cover and sprayed a bit of carb cleaner straight down the throat.  I expected it to start, run for a sec, and then die.  It won’t even turn over when it has straight fuel in it.  I also tried taking off the spark plug, spraying a small amount of fuel straight into the cylinder, and replacing the spark plug.  It won’t even turn over or try to catch for a sec.   So it can’t be a carb issue.

My next guess was “spark plug” or electric issue.  However, pulling out the spark plug and grounding it while pulling the starter cord produces a good spark.  So it can’t be a spark or electrical issue.  I also assume it can’t be a pull-starter or kill-switch issue, because either would prevent it from making good spark.

I even took the chain and bar off just to give the engine a really easy time for testing.  It made no difference.  The saw won’t even catch or sputter for a second.

What else am I missing?  Where have I gone wrong?

[barbender]

 So it must actually turn over if you are getting spark? It's kind of confusing the way you're describing it.

 How does the compression feel?

[Colonel428]

Take the muffler off and look at the piston for scoring marks...

[rusticretreater]

An engine needs three things to run, fuel compression and spark.  As you have said you provided some fuel and you have spark, you must not have compression.  Do you feel compression as you pull start?  

Please tell us what brand and model the saw is.  

[rworkman98]

So it must actually turn over if you are getting spark? It's kind of confusing the way you're describing it.

How does the compression feel?

Sorry if I am describing it poorly.  The saw is making the "woof-woof-woof" sound that I normally associate with small engines that will not start.  However, it will not ever "catch".  I am feeling the normal resistance when doing the pull-start.

An engine needs three things to run, fuel compression and spark.  As you have said you provided some fuel and you have spark, you must not have compression.  Do you feel compression as you pull start?  

Please tell us what brand and model the saw is.  

Could be.  Is there an easy way to test compression without specialized tools?  When I pull the start, I feel the normal resistance which I associate with compression.  The saw acts as it always has before "catching" and starting.  Where I am confused is that if I have verified spark, and I have cheated by spraying fuel straight into the cylinder, it should start and run for a sec regardless.  

It is a PoulanPro PP4218.  I'm aware it's a "lower-end" saw, but I'd really like to avoid the > $400 of a better saw right now, and have several more trees I need to get down this week / weekend. :(

Are there any common things to check that cause compression to fail?

[lxskllr]

Like the colonel said, take the muffler off and look at the piston, and inspect the parts of the cylinder you can see. If it's gouged, the troubleshooting can stop there. That's new saw time with a poulanpro.

[Jack S]

Don't forget a plugged or severely restricted muffler will shut down an engine also

[TroyC]

Check the flywheel for a stripped keyway. That will give you a spark but won't run.

A clogged muffler should at least do a few pops before the back pressure stops it. Had one like that a while back from a friend running too much and cheap oil. Cleaned the screen and it was fine.

When you try to start it  and it won't start, pull the spark plug. Is it wet? If so, I blow air thru the carb as I rotate the crankshaft. Don't overpressure it or you may damage the reed valves. Also blow some compressed air thru the spark plug hole. Put a new plug in and try again. I have several Poulans ans sometimes they can get finicky. Occasionally just changing to a new plug fixes them.

[rworkman98]

Take the muffler off and look at the piston for scoring marks...

There are some pretty good scratches / slight gouges on the outside of the piston.  So I guess that means it can no longer hold a vacuum & compression is gone?  Or something else?

[lxskllr]

That'll cause low compression, and a no start scenario. That saw's pretty much done. A pro saw would be worth repairing, but the effort and cost is prohibitive for your saw.

[JonathanPace]

Not sure if this helps, but came across a few videos on YouTube about reasons why a chainsaw may give issues.  ???

Chainsaw WON'T START or HARD to START? Try these easy fixes! - YouTube

[rworkman98]

Thank you all for the help!  Since it appears unfixable (or at least not worth fixing), I have just picked up a Husqvarna 455 Rancher.  I hope it serves me longer than the 6 years the Poulan lasted.

[lxskllr]

That'll be a good saw for you. Six years from the poulan isn't bad. That's $25/yr, and it cut wood. People are pretty down on the old poulans, but they are what they are. For the cost of a bar and chain for my 661, you get a whole saw that cuts wood. The older pp designated 4218s were better than the newest pr designated saws, but even they cut wood. The 5020s do suck, and while they cut wood, they get you wondering if a bowsaw might be better  :^D

Anyway, that rancher is a nice step up. Enjoy your new saw  :^)

[Al_Smith]

On Poulan it just depends on what model it is .FWIW I have an S25 DA I bought new in 1974-75 that still runs as good as it did when new .---32 to one oil ya know . 8)

[DHansen]

Str 8 30 weight?   ;D

[Hilltop366]

On Poulan it just depends on what model it is .FWIW I have an S25 DA I bought new in 1974-75 that still runs as good as it did when new .---32 to one oil ya know . 8)

I can't believe you bought a new saw!  ;D

I know it was almost 50 years ago but it still counts.