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Stihl MS 250 won't run after starting

Started by McRuss, February 19, 2016, 03:16:59 PM

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McRuss

Before someone jumps in to say it, I did a search and didn't find any help.

My issue seems to be unique though I doubt if it is.  Here it is:  this saw gets very little use so between uses, I dump the fuel and run the carb dry.  No no old fuel issues.  This time I put a new plug in right off the bat.  Now it will start on full choke and run if I 'twiddle' the choke between full and partial.  it will not run on partial choke nor with choke off.  Gas is new, mixture is correct.  I HAVE NOT touched the mixture screws nor the idle screw.  So help would be appreciated.
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

beenthere

Welcome to the Forestry Forum.

I also have the MS250, but not the problem. So am interested in a solution.

Click your forum name, and you can add your location to your profile. Helps to have that when answering and reading posts.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

slanted6

My 025 acted the same way a few years back. Turned out to be the impulse line.

Texas-Jim

Off top of my head the 250 doesnt use impulse hose. It has a port where carb mounts up. It does sound like fuel so the carb be my first guess. Cleaning it is easy and id bet you find diaphram is stiff. Dumping the fuel doesnt ensure trouble free storage, it does help. As a rule i use moto-mix as a storage aid, its high so i dont run it as fuel. When im done i dump regular gas out and fill it with moto-mix then run it till its purged the carb. Reason is, it uses synthetic oil and has a stabilizer in it, it has a two year shelf life.
What we do in life echoes through eternity.

smmyb123

It sounds to me like the diaphrams in your carb have dried up/ hardened. A new carb for that saw is about $35, you can test for fuel related issues by spraying some carb cleaner/ starter fluid into the intake while holding the throttle open and then attempting to start the saw. If the saw revs up on the starter fluid then its probably the carb.

McRuss

Quote from: beenthere on February 19, 2016, 03:29:47 PM
Click your forum name, and you can add your location to your profile. Helps to have that when answering and reading posts.
Well, I don't see an option for either adding location (Texas Hill Country) or a tag line (don't have one.)
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

beenthere

McRuss
Also, can get at your profile by clicking the menu tab along the top that says "Profile" and click Account settings and Forum Profile.  Should be available to you.
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

joe_indi

McRuss
Two possibilities:
1. You need to change the pick up body (filter in the tank
OR
2. The impulse hose that is connected from the engine block to the red portion of the body, just below the carb (on the outside) has come loose from its connector.
Look into the narrow space between the fuel tank and the red portion. You will barely see a tube there. move it with a wire or narrow screwdriver to see if one end is free or still fixed to the body.
Joe

McRuss

OK, the impulse hose is connected (yes, there seems to be one on the 250.)  The filter in the tank is on the list of things to do.  But first, I noticed an abnormal looking thing on the carb by the adjusting screws.  Photo attached.

It looks like what ever this is, it needs to be re-seated but doesn't want to go.  It will turn but I would like to know what it is or does before I go any further.

Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

McRuss

And now, to remove the carb....just the two nuts that hold the intake piece/air cleaner to the carb/engine?  I've never had a carb off of a chainsaw before, used to working on motorcycles.....
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

Texas-Jim

That thing in the pic is a vent, it doesnt have an impulse line. I can look tomorrow but im positive it gets its impulse through a port.
What we do in life echoes through eternity.

joe_indi

Yes that is the tank vent. The impulse hose is not that easily visible. I will try and post a diagram or picture

McRuss

Tank vent?  It isn't anywhere near the tank.....but there is a hose running from the tank to the engine (and not the fuel line) that I thought might be the 'impulse hose.'  OK, so maybe what I took to be the impulse hose actually goes to that gizzmo in my photo.  I'll have to take a closer look at it tomorrow.  Should it be 'seated' in the rubber 'socket?'  I couldn't see what it was connected to but it didn't want to either come out or go in.
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

joe_indi

Here is a diagram of how the impulse hose runs from the cylinder through the manifold to the carb


joe_indi


beenthere

joe_indi
As always, excellent instructions and tutorial from you.  smiley_thumbsup
south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

luvmexfood

Quote from: beenthere on February 21, 2016, 01:28:35 AM
joe_indi
As always, excellent instructions and tutorial from you.  smiley_thumbsup

Yes Joe. Thank you for your imput to the forum. Taking the time to make the color drawings for someone halfway around the world is going a step above.

With that said not forgeting about the good advice provided by other forum members.
Give me a new saw chain and I can find you a rock in a heartbeat.

McRuss

Wow!  Joe, I am impressed!  Thanks for the great photos and info.  I had the carb off and cleaned it today.  Cleaning the carb resulted in being able to start it at full throttle but it will not idle.  I ordered a diaphragm kit to replace both of them, hoping that will solve the problem as they don't look too good.  And I understand now what the 'gizmo/breather' is I was looking at and how it attaches. When I have the carb back off to install the diaphragms, I'll look more closely for the impulse line.  It may be easier to see then.

So until then, Thanks to all who have responded to my query!
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

joe_indi

Quote from: luvmexfood on February 21, 2016, 03:11:49 PM
With that said not forgeting about the good advice provided by other forum members.
More thanks actually to the other forum members!
The next time I have a similar issue I always follow their suggestions also.
So, it is a continuous learning process for me too.
"The older I get the more I learn"
With all the help from the Forum.
Joe

deerslayer

When you replace the carb parts, make sure to clean the tiny carb screen. It's about the diameter of a pencil eraser and is a screen that fits into a shallow hole.
Too many chainsaws, not enough wood.
Stihl, Husky, Craftsman, Mac, Homelite, Poulan. Some live here, some just passing through.

McRuss

"Oh no, he's back!" 

Yes, I'm back.  Put a carb kit in the saw, made sure the screen was clean along with the rest of the carb.  All looked good so back together. 

Fast forward a couple hours

Filled it with fuel and same symptoms.  It will start and run at full throttle (pardon me if I'm wrong but the pulse line/system must be working if it will run and as near as I can see the line is attached) but will not idle.  I can fiddle with the throttle to keep it running but it runs rough in between idle and full throttle and immediately dies when throttle is released.
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

joe_indi

Remove the carb, pump a few drops of oil into the impulse hole. Pull the starter. If the impulse is good the impulse hole should spit that oil out.
Joe

old2stroke

When you cleaned the carb, did you remove the welch plug covering the idle jet and the transfer ports?  When a saw won't idle and doesn't respond to the low speed adjustment screw, this is something that has to be done to make sure dirt hasn't found it's way into the well under the plug.  Does that carb have a nozzle check valve on the main jet?  If it is stuck open it can let air bleed back into the idle circuit and lean it out to the point where it won't idle.
Not too many saws.  Not enough storage space.

McRuss

Quote from: old2stroke on March 02, 2016, 03:56:19 PM
When you cleaned the carb, did you remove the welch plug covering the idle jet and the transfer ports?  When a saw won't idle and doesn't respond to the low speed adjustment screw, this is something that has to be done to make sure dirt hasn't found it's way into the well under the plug.  Does that carb have a nozzle check valve on the main jet?  If it is stuck open it can let air bleed back into the idle circuit and lean it out to the point where it won't idle.

Sorry but I'm not sure what or where the 'welch' plug is so I probably did not remove it.  And I have no idea if the MS250 has a nozzle check valve on the main jet.
Guns are like parachutes:  if you need one and don't have one, you probably will never need one again.

old2stroke

If you get the make and model numbers of the carb, a blow up diagram of the parts can be found on the internet and it will list a nozzle check valve if it has one.  Maybe someone will jump in who is familiar with that saw model and will know the carb.  The welch plug for the idle system is a round disc in the body of the carb covering the area where the idle jet (small hole just on the engine side of the closed throttle plate) and the 2 transfer ports (small holes just behind the closed throttle plate) are located.  Fuel from the low speed adj screw is delivered to the well that this plug covers and is then sucked out through the little holes into the air stream through the carb.  The holes are quite small and are easily blocked, so if you remove the plug, you can gently push a small wire through the holes and ensure they are clean.  You remove the plug by carefully drilling a small hole (1/16") just through the plug, then sticking a pointed tool in the hole and prying it out.  You need to replace it with a new plug the same size (sometimes includes with a rebuild kit).  You place the new plug in the cavity with the dome side up, then flatten it with flat end punch to seal it in.  Sounds messy but really quite easy to do.  There should be another plug covering the main jet, but lets find out if there is a check valve on the jet before digging it out.
Not too many saws.  Not enough storage space.

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