Stihl Chainsaw Won't Start

[Bill George]

My Stihl MS170 sat for years before now I need it. Fresh gas with Stabil pull and pull, nothing. Pull the plug, damp from gas replace plug, pull and pull nothing. Pull new plug lay on top, pull looks to be spark but not fat. Pull cover off, starting fluid into air intake to carb, nothing. Zero, thinking a weak spark ordered new coil and new Carb just in case. Since it would not start with Either I thought that was a clue. Comments?

[Edward Weber]

You have spark, you sprayed in starting fluid, so somthing should have at least given you an indication of the issue. Does it even try to fire? Is the chain brake engaged? Have you checked for a clogged fuel filter (stabil or not)

[jack duren]

I cant imagine you needing a new carb if you’ve used it recently. Fuel issue?

[Tom M King]

One thing you can check is the coil gap. Too wide and the plug won’t fire under compression. Probably a YouTube video. I have a gauge but some use a dollar bill.

Several things it could be. If coil gap is okay and it is firing the plug, I would do a pressure test, but you need a few things to be able to do that. Won’t pad pressure test, then you start looking for the leak.

Just throwing parts at it is guesswork. Guesswork is as good as any only when you get lucky.

[Andrew Hughes]

My experience with chainsaws is somewhat limited. One of my good running saw sat for a long year or more without being started the gas left a plastic like varnish around the diaphragm in the carburetor. I carefully cleaned it out and never left gas sit in the saw again.
Good Luck

[Tom M King]

Especially if it sat for a period of time with ethanol gas in it.

[Bruce Wrenn]

Check for rust on magnets and coil assembly. Twenty bucks will get you a new magneto from Amazon

[Bill Dufour]

Why would you add anything to fresh gas? Check plug gap. for some reason some folks think they are factory gapped.
BilL D

[Bill George]

Stabil in everything, you fill the gas tank use it a couple times and then it sits.

This chainsaw is my fault it set for 5-6 years. I checked the coil yesterday and the gap is good so I am not replacing it now, going to try to clean the carb. In case you folks have not noticed there are no idle or fast jets you can remove and clean and very little else thanks EPA. I have had good luck replacing the carbs with the ones from China so If I can not get it clean do to limited access I will replace.

NO Ethanol ever in small engines at least I don't need to contend with that!

[Ole Anderson]

Carb varnished up.

[George Yetka]

Bill

Everytime I come up to a no start situation I try for 30 minutes then get on computer and replace everything. Its not worth the $20-40 in parts to fight it, just replace it. Your back will thank you.

[Tom M King]

My bet is on the carb putting it back to work now.

[Tom M King]

While you’re waiting for the carb to get there, pull the spark arrestee screen and see how clean it is.

[Alan Rutherford]

Bill

Everytime I come up to a no start situation I try for 30 minutes then get on computer and replace everything. Its not worth the $20-40 in parts to fight it, just replace it. Your back will thank you.

Yep. New carb still in the Amazon package waiting for me to install it. That's when I'll find out if the -1 version of the carb was the right one or I should have ordered -2, -3, or -4. No clue in the listing - they all fit this model - and I haven't taken it apart yet.

[Alex Zeller]

An old Canadian neighbor taught me a trick. He gave me an old igniter coil from a furnace. He wired up a plug on the wires so it could be plugged in and create an arc. The trick is, BEFORE plugging it in, to put the spark pug on one of the terminals and a screw driver touching the base of the plug to the other terminal. Be very careful. Plug it in and let the plug arc for 5 minutes or so. It'll burn off any bad gas. After unplugging it the plug will be very hot but you'll be able to reuse it.

[Larry Frank]

Ok had a Stihl for years and drained gas every year. It seemed harder to start every year and I got older and my shoulder sorer. I sold my Stihl and bought an Ego battery one. It cuts great and starts easy .

[Bill George]

Well despite fresh gas mix, new plug, removal of the spark arrester screen and new carb still no start. I even tried another coil and that did not help so back to the OEM. I think it has to do with timing and I found info online that suggests that the key way might be compromised. There is also info regarding altering the timing on this engine to increase the output power. I will get into that later on as this project is going on hold as I have other things to get done.

[Edward Weber]

The distance of the coil from the flywheel will effect the strength of the spark. The key way on these saws has been described as "notoriously" sloppy, + or - 5 degrees in some descriptions.
the combination of these things can certainly 1. provide spark, 2. fail to start.

[Bill George]

From what I found out the gap or distance also has some effect on the timing. The magnets are marked N & S for a reason that needs looking into when I get more time. Right now we are headed toward a early spring.

[Tom M King]

Might be worth pulling the muffler and locking at the piston. https://www.youtube.com/watch?v=Iay9-rmhWEA

My next step would be a pressure test. Might just be a leak in the impulse line, but could be other places too. I doubt it's anything to do with timing.

[Bill George]

Might be worth pulling the muffler and locking at the piston. https://www.youtube.com/watch?v=Iay9-rmhWEA

My next step would be a pressure test. Might just be a leak in the impulse line, but could be other places too. I doubt it's anything to do with timing.

I had it, off piston looks fine, and good compression. Lots of experience with both 2 and 4 stroke engines. Its getting gas , plug shows that, but no fire at the right time or not hot enough spark causes it not to start.

[Edward Weber]

I had it, off piston looks fine, and good compression. Lots of experience with both 2 and 4 stroke engines. Its getting gas , plug shows that, but no fire at the right time or not hot enough spark causes it not to start.
While I don't typically recommend products, I strongly suggest an NGK spark plug.

[Bill George]

While I don't typically recommend products, I strongly suggest an NGK spark plug.
That was replaced first and always a NGK.

[Tom M King]

I had a friend a long time ago that raced motorcycles. One of his sponsors was Champion sparkplugs. I saw him one night repainting some sparkplugs and doing a pretty good job of putting Champion on them.

[Bill George]

Went out to do some checking on the saw and this time found NO Spark, WT heck!! Always had it before?? So I put on the Made in China coil that I had and did not use because it Had Spark. After a few pulls and now starts and runs. Headed out to cut off a stump so I can get the mower back in that area. I did no adjustments to the Chinese Carb I put on a week or so ago. Never had a problem with the better grade of Chinese carbs I buy.










'

[Tom M King]

Glad it was something simple and you got it back to work.

[George Armstrong]

What should the gap be on the coil?

[Tom M King]

Different saws ask for different gaps but if I'm remembering correctly Stihl saws call for .2MM to .4MM depending on the saw. Bigger saws with stronger coils use the larger gap. I have two different gauges that cover my three saws. Some people use a new dollar bill but that always seemed like it had a guesswork factor to me.

[Bill George]

I went by what Chickanic put in her video , business card. The one I used measured about .014 inch or .35mm . It must fit under both poles of the coil. I use premium grade non Ethanol gas, with Stabil unless I know I am going to use it right now.

I am going to guess since the OEM coils are replaced by the thousands, they have a design or manufacturing issue.