Hi I have a stihl 250 chainsaw which when I pull the rope to start it snaps back and almost pulls the rope handle out of my hand but when it does start it runs great,I am wondering if is a build up of carbon and if so how can I clean the carbon out of the of cylinder without dismantling the saw???
or could the it be pre ignition?
thanks don
 
Push in the compression release on the top of the saw and you won't have that problem.
I start mine cold with the compression release in and the choke on. pull till it starts or tries to start. Release choke, if it just tried to start pull rope with choke off, if it yanks your hand back push in compression release, pull till it starts.

That is what works for me, your saw may have a different temperamental attitude.
 
My MS250 doesn't have a compression release. I bought this one new two years ago, and it is doing fine. But I have a ten-year-old MS250 that developed the same problem the original poster described. I have that saw on my workbench, dismantled. I haven't determined the cause for the problem, but I read in the owners manual that you should not use fuel with a lower octane rating than 89. I had used 87 octane regular no-lead since it was new. I figure it was caused by that or ethanol. In my new saw I am using 93 octane fuel.
Butch
 
I have that issue (problem?) with one I bought two years ago. It was that way from the time I bought it. I just thought it was the nature of it. Otherwise the saw is fine. MS250
 

One I have is like that from new, seems worse at first start of the day. Found I just need to grip and pull hard enough to go past the hard spot. Always used the recommended fuel and still oil.
When warm I just start in the idle position and just notice a normal pull.
 
Two possible causes.

#1 is the rope too short? If it has ever broken and then the handle got put back on with the rope shorter - it has less mechanical advantage because the rope sits on a smaller circle. Very common for that to happen.

#2 I don't know how your modern Sthil oil-pump works. On older Sthil saws - they had gear driven oil pumps for the bar that sat inside the crankcase. Often the oil pumps would leak bar oil into the crankcase and make them very hard to pull the rope.
 
Sounds normal to me.

When it is worn out and the compression goes down, it will not do that.

Dean
 
I am wondering what series saw he has an older 250, 1127 series maybe,(250, 290, 310's I believe) if so, its external like my 390 which is an 1127 series The worm gear drive oil pump sits in the engine housing behind the sprocket surrounding the crankshaft where it projects through the engine housing and is driven from the other gear that slides over the crankshaft, when the clutch is engaged, if I remember correctly. I don't believe you can get bar oil into the engine with this arrangement.

What you said about the rope being short, I think if I don't get the pull right, it does that, meaning I've not pulled it far enough, one does have to keep a good grip on the rubber handle when pulling one of these over without the decompression button/lever. My MS 390 will do that.
 
I don't know about carbon in the combustion chamber, I recently inspected the piston and cylinder in what should be the same series or family of saws, been in use since '02, top of the piston was the only part that had a little carbon and or black substance.

One thing you can check is the muffler anti spark screen, those load up with carbon, not much on mine, but enough to clean.

Not sure what air filter you have, but mine likes those kept clean, regular interval, more if I am cutting dry dead wood, more dust than chips.

Mine with meticulous care, will start cold in 3-4 pulls, 1-2 on full choke, pops off, if you are quick enough to move the lever up one notch, it will stay running, if not it will in 2 pulls. Hot, usually one pull, no choke, consistently.
 
(quoted from post at 05:48:03 11/13/14) Sounds normal to me.

When it is worn out and the compression goes down, it will not do that.

Dean

same here.
lots of pull start engines here.
Every pull, you can never relax or get sloppy.
Inch it to find the compression, then let the rope recoil, and go violent....every time.
Engines are just waiting for you to relax your hand or shoulder.....to bite you.
Pull ropes, hand cranks on tractors, kicking a Harley....all the same...do it like it just insulted your mother/sister/wife. :D
 
In all my small engine, I use premium grade fuel-93 Octane with no alcohol. For the amount I use, maybe 30 gallons each year, it is a small expense.

It prevents fuel line problems, run on when I shut the larger engines off, breakdown when stored and other problems.

Since often, the service station has a single hose for all grades, I often put the first gallon into my vehicle and fill my containers after that. That long hose can hold quite a bit of alcohol enriched fuel.

I usually try to find a place that has a dedicated hose to each fuel grade.

This may sound terrible to some but I have never used Stabil in any fuel tank since using premium and have never had a problem.
 
Sounds about right for a 250 to me too.

I had a standard MS250 that was almost impossible to start. I actually tore up a leg of my jeans and cut my leg trying to start it.

I traded it back in for an MS250 with EZ Start. Solved the problem. The EZ Start is great. Made a whole different ball game out of it.
 

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