Stihl Cement Saw not starting - frustration

[51Plymouth]

Stihl TS-350 2-stroke cement saw not starting. Bought used 5 months ago. Seller demonstrated that it started in one pull and idled great. Then sat in my barn 4 months. Gas tank has small crack in it so most gas leaks out over a day. Added fresh mix a month ago and it started fine. Used it for about 30 minutes. Sometimes stalled when I pulled the throttle. Restarted immediately and I just played with and pulled the throttle slowly. Used it two weeks ago for 15 minutes, same stalling but at least it restarted and I got the job done.

Today I go to use it - started in about 10 pulls. Worked good for about 10 minutes. Then stalled with a very small backfire. Seemed like intake backfire. Now does not start at all. I thought my mix might have been too strong (might be 32:1) so I added some unmixed gas. Still not starting. It currently has no mix and only a tank of regular gas. I thought if it started I would turn it off immediately and put in mixed gas.

Here is what I tried:
Heating and drying spark plug with propane torch. Sometimes the spark plug was wet with fuel other times dry. Tried other spark plugs. There is all kinds of visible spark when pulling rope while watching spark plug.

Took apart carburetor - Tillotson carburetor. Nothing visibly wrong and it was totally clean. Blew everything out anyways. The one diaphragm or whatever it is with the steel part on the back might have been a bit stretched, but could be okay.

Blew fuel line with my breath. It is clear along with the screen on the end of the hose in the tank.

I put a few drops of regular gas in spark plug hole. Pulled rope. Nothing. When I took out the spark plug there was a slight mist of smoke rising from spark plug hole, but not a hint of firing.

What else can I try? There seems like there should be good spark and I put a few drops of fuel in the spark plug hole. Shouldn't it at least fire and run for a few seconds if nothing else?

Did I miss something? What else and how else can I test anything? Thanks everyone.

 

[Warstud]

Start by replacing the leaky gas tank...may be sucking air...plus it's dangerous. Then go from there.

 

[51Plymouth]

Oh yeah, I forgot to mention that the seller repaired the tank with epoxy so it is fairly sealed. It might only be very slowly leaking around the cap threads or seal.

Warstud, I appreciate the advice about the danger of the leaky tank but I'm only going to need this thing to run about 10 minutes every couple of months so I am trying to avoid tank replacement.

If I understand you right, you are saying the tank needs to be 100% completely sealed? If the filter screen in the tank is below the fuel level is this adequate for at least test starting or no? So there should be no vent anywhere on the tank to replace the gas that the carburetor takes out with air?

I noticed on top of the tank beside the carburetor there is a hose barb molded into the tank that has a piece of hose sticking straight up with a screw in the end. This hose was cracked from age. For a temporary measure I wrapped the hose in tape to cover the hole. No improvement with the non-starting.

I also forgot to mention when I pull the rope it feels like great compression.

 

[eljefino]

Is there a primer bulb on it anywhere? I had a 2-stroke weedwhacker where apparently the tank was pressurized and forced the fuel up the hose. There were two hoses; the 2nd one somehow pressurized the tank. When I opened the cap there was a pressure whoosh.

 

[51Plymouth]

No primer bulb. There is a choke sliding lever, for choke on or off or anywhere in between.

I forgot to mention when it was running before, sometimes pulling the throttle would cause it to slow down and stall. I left the choke in the middle and it ran good enough in that position. Not ideal of course but at least it was running and cutting good enough.

 

[Clevy]

It's a carb issue. Those saws are very simple engines which is what makes them so great. I'm betting there is some form of gasket sealing issue.
How does it sound when you pull it over. Is it a deep type sound or higher pitch. Deep is too much fuel.
When our plug gets fouled I have to lock the trigger at wot then pull the rip crud to start it.
Don't let it run lean or the piston will melt. I think its supposed to run fuel at 50-1 but maybe google to confirm.
Good luck

 

[51Plymouth]

Yes the saw seems very simple. Unfortunately I can't figure out what is wrong. I think I would rather work on a complicated car.

I agree when it was running it seemed like a carb issue. Now that it is not starting at all - I'm still lost.

I have the air filter off so the sound when pulling the cord might be different than normal. It sounds different with the choke on and off. One way makes a deeper sound.

I've pulled the cord about 100 times, all with different combinations of choke and throttle setting, different spark plugs, blow drying the spark plug, blow drying the cylinder, putting in a few drops of gas in the cylinder, etc.

It would be nice if it ran for 5 minutes so I could finish the small cutting job I was on.

 

[doitmyself]

Seems like you know about basic engine diagnoses: fuel,spark, compression, timing.

Quit putting raw gas in there! Oil mix is not the problem.

Spend $2 and put a new, correct spark plug in there.

Check the fuel filter for clogging.

That exterior tank hose with screw is probably the breather. Saw won't run with a vacuum condition in the tank.

CHECK THE FUEL LINE FROM THE TANK TO CARB. They often crack and result in sucking air.

Make sure both the carb and the piston are mounted tight, again to avoid air suckage.

TAKE OFF THE MUFFLER COVER AND CHECK FOR A CARBON BLOCKED SCREEN. Another common problem caused by poor carb adjustment, bad fuel mix, and too much idleing. Same effect as Eddie Murphy sticking a bananna in the exhaust pipe.

DOES THE SAW SEEM TO HAVE COMPRESSION?......"back pressure" when you pull the cord.

You need more than a few drops poured in the hole. I use a "small" teaspoon. A great trick that sometimes gets a saw running and maybe unsticks the carb?

Air filter is Clean???? Not fuel soaked...equals plugged.

The carb still might require a rebuild kit....very cheap. Also, learn how to adjust the carb....high/low/idle speed screws.

We covered fuel, spark, compression. Timing? Don't rule out the ignition system going bad, but I have rarely ever seen that happen.

Best of luck. If you are brave, join arboristsite and ask the gurus over there.


HERE'E THE OWNERS MANUAL: http://www.stihlusa.com/WebContent/CMSFileLibrary/instructionmanuals/TS350_Manual.pdf

High/low carb screws should only be 1/4 turn out to start.....very odd, so small.
Don't over tighten them to seat and ruin the screw/seat.

Fuel mix is 50/1.

 

[doitmyself]

Check that on/off switch also.

 

[51Plymouth]

UPDATE - FIXED ! Thanks everyone, here's what happened.

Yesterday saw stopped running and did not restart, as in my first post. Other things I checked yesterday after my post:

My mix was incorrect. Needs to be 50:1. I was more like 32:1.

Incorrect spark plug by former owner. At least it had the right reach in the cylinder.

My gas tank breather was missing, replaced before me with a hose which now has a crack in the side. I guess the tank is breathing, but I think the original breather has a check valve or something so gas doesn't leak out if the saw is on its side.

Fuel filter was clear, fuel lines in great shape. Carb mounted tightly. Air filter was clear.

Today I took off the muffler to see what I could see. Piston, rings, bore looked fine. The muffler was not clogged, and someone already removed the spark arresting screen at the outlet of the muffler.
I tried to start it - nothing.
I double checked the spark - almost no spark. Sometimes there was no spark and when there was spark it was so faint I could barely see it. That was really strange because yesterday there was lots of spark.
I checked the switch - it was fine.

I gave up did something else for a while. Later I decided to go to the local Stihl dealer to try to get some free advice and see if they have some sort of spark intensity tester. Gentleman behind the counter was really nice. Gave the saw a quick look over for free. That is when he said that it wasn't a TS-350 at all. It says that on the blade attachment, but someone put that blade attachment on a regular Stihl 08s (newer version) chainsaw. The engine part did not leave the factory as a cement saw at all.
He has no real spark tester, he said either there is spark or there isn't. He noticed the spark was so weak he didn't even get a shock from the spark plug. Also he said the compression wasn't great. I still have to strain to pull the rope. New saws must be really tough to pull the rope.
Without removing the flywheel he could not tell if it was an old model that had points, or newer with electronic ignition. He priced a new ignition module for me, it was $250! He realized I probably didn't want to pay that much to repair this particular saw. He suggested I could pull the flywheel and clean the points if it had them, or blow dust and debris from around the module and maybe then it would have spark.
He spent about five minutes looking things over and talking to me for free. I thanked him, I was very grateful he was willing to do that. A very nice guy.

I went home and removed the flywheel. Normally there is a special puller but I held the flywheel up carefully around the edges with my fingers and carefully whacked the crankshaft with a hammer a couple of times. The flywheel came off and I immediately spotted a problem - the flywheel key was COMPLETELY SHEARED OFF! Fortunately the crankshaft and flywheel were still okay.

I went back to the dealer for a new flywheel key and a correct new spark plug. $5 for both.

Back home I carefully tapped out the broken flywheel key. There were little pieces of key everywhere. I think a few were closing the gap between the flywheel and ignition module. I blew everything out and put in new key. Reassembled and checked spark. Still kind of wimpy spark but at least it had spark and was consistently there.

Fired immediately and almost started on first pull! I ran it for a little bit and seems fine except needs some carburetor adjustment. Stalled a couple of times but it restarted right away.

Yay!! What a wonderful feeling of having operating equipment.

Good thing I pulled the flywheel, I would have never guessed that the flywheel key sheared. I didn't realize that cement saws or chainsaws would ever shear their flywheel keys. I also forgot they had them.
I guess cement saws and chainsaws take hardened flywheel keys in case anyone is wondering. (The sheared off one was also hardened and appeared to be the correct one.)

Also of note, since this is a Stihl 08s converted to a cement saw, I do not have the large cement saw air filter. I only have the original 08s air filter. The previous owner put a thin sponge around it to help keep out cement dust. I noticed that a while after I bought the saw and wondered why I did not have large air filter. The dealer thought it would not last too long as a cement saw due to dust ingestion. I have been carefully keeping dust away from the filter area, which is underneath the handle. I think it will last a long time because it is only for personal use around my house and buildings.

 

[lars11]

Good work!
Anyways, all those sheared flywheel keys, why is that happening? What kind of violent events are shearing that key? Why is nothing else damaged if the key is ripped at a sudden hard stop or something? Or are the flywheels not tighten enough so it slowly eats away at the key?
I have never seen it myself but read alot about it. Please enlighten me!

 

[51Plymouth]

About the sheared flywheel key, it only happened once to me with this saw, so far. I am not sure why it happened. Here are the only clues I have:

I bought the saw used five months ago. At that time it had an almost worn out black metal cutting blade (for cutting metal) on it. Ran great at time of sale.

I found out later it is not a real cement saw, it had the TS-350 cement cutting wheel attachment put together on a formerly regular Stihl 08s chainsaw. The flywheel could have been taken off and put back on during this transformation process. It looked like someone might have ground down the case with a grinder for the flywheel to fit. I am not sure if I have a cement saw flywheel or chainsaw flywheel.

What I think people should do, when they put a flywheel back on, is to run the saw for a little while and then recheck to make sure the flywheel is still actually tight. Maybe the previous owner did not do this.

Whatever flywheel I have, the tapered fit looked properly sized, and the flywheel appears to fit well.

After purchase, I used the saw for cutting cement over the course of a month for a total of about 45 minutes. It was several different cuts, with stopping in between, changing blades, etc. I was using "used" concrete blades (black material), and not diamond blades. Most blades were about 10 to 11 inches when I started.

I took my time cutting, there were absolutely no violent events or sudden stops while I was cutting. I noticed with my saw there must be a clutch for when the blade grabs because if this happens the blade stops turning with the engine running. Either that or my drive belt is loose but I don't think so.

The former owner may have had sudden stops or abused the machine, I have no way of knowing.

The flywheel may have been a little bit loose for a long time and the key finally wore out from that.

Surprisingly after this event, there appears to be no other damage. The slot in the flywheel and crankshaft looks like brand new. There is no damage to the slots at all. All of their edges are still perfectly square.

 

[doitmyself]

Excellent. I have never seen a sheared key on a 2 cycle engine in over 35 years (4 cylcle, yes). Maybe a bad ignition system once (can't remember).

There were numerous issues that clouded the diagnosis (plug quality, fuel quality, etc.)and initially you thought the spark quality was o.k..

The dealer visit was the key that lit up the light bulb in your head to remove the flywheel.

This happens to me often. With blinders on, I assume what might be wrong. Often, when I bring someone else into the diagnosis, they ask a key question, and bingo, "why didn't I think of that?" I know the feeling well, when you found that broken key........YES!

Good for you! And, another lesson for all of us.

 

[Bullet]

I got a sthil chain saw that is stuborn and sometimes won't start. The first time this happend I pulled an replaced the plug, but nothing. The plug sparked no prolblem. Quick start dind't help. I tried spraying carb cleaning in the air intake. I pulled the flywheel to make sure the key didn't didn't fail. Finally I sprayed WF40 in the carb and it fired up. Sometimes it starts fine sometimes not. When ir doesn't start I dry the plug and spray WD 40 in the carb and it fires up like new.