Saw won't run with chain and bar attached!

[skier-hughes]

Hi,

I have a sthil MS250.

It's been running fine, but yesterday on starting it would splutter and stall.

It starts fine, but just won't run.

I took the chain and bar off to have a check and cleaned all I could see (I'm no mechanic) using an airgun to blow away all dirt.

Tried it and it ran like a dream.

Good, that's solved it I thought.

Put bar and chain back on and back to spluttering and stalling.

I loosened the chain right off as much as I could in case I'd overtightened it (I have had and been using this saw for 6 years).

Just the same.

Took bar and chain off, runs like a dream again, revs, idles no problem.

 

Only thing I didn't do, that I'm thinking I could have done, is fit bar but no chain and tried it.

 

Anyone any ideas, or should I just take it in to a dealer to be sorted?

[Llama777]

Could be the sprocket in the nose of your bar if the chains not running when you rev the engine

[Little Al]

As said check nose sprocket runs free binding /tight spots, check clutch & sprocket is not locked up ( sprocket bearing) sprocket teeth for wear/damage, check chain drive links (damage, wear, bent)mount chain & bar on saw, (gloves on)& pull chain around bar, if tight/locked up check for fault.( Please forgive chain brake not engaged ?/ problem with brake mech)usually problem getting clutch cover off with brake problem

[arbandy]

Had the same problem with a 20T. Turned out that the pressure of the chain was enough to pull the crank to allow air past the bearing seals and mess with the fuel/air mix. Take the bar and chain off and check for movement of the shaft . If there's any then that may be your problem. my solution was to buy another stripped down crankcase from my local chainsaw repair shop. It had a seized piston from another cause. then swap all the bits over and it hasn't missed a beat since. Second option and the most reliable long term is to replace the crankshaft bearings then you will have an almost as good as new crankcase pressure seal again .

[skier-hughes]

@Llama777 & Little Al The end sprocket turns freely, the chain will run freely, I can pull it round by gloved hand quite easily. The chain is virtually new, only used for two days home logging and all looks good. There is some wear on the sprocket in the housing.

@arbandy I'll check the shaft and see. Looks like it'll be going in for repairs.

 

Thanks.

[Gray git]

Check your clutch springs, if 1 snaps the clutch won't disengage at low speed and stall the engine.

This would be why it will run with no bar on as no resistance, did you notice if the sprockets were spinning when you had the bar off and the saw running?

 

sent while pretending to do something important on my mobile.

[skier-hughes]

I'll check that as well, cheers.

[SawTroll]

I'll check that as well, cheers.

 

It more or less has to have something to do With the clutch or clutch bearing, if the bar and chain is OK, and the drive sprocket serviceable.

[skier-hughes]

Started it up, the sprocket turns wildly when idling. I gently, with a gloved hand tried to stop it turning and it spluttered and stalled

[MrHairy]

Sounds like the clutch springs aren't doing their job. Stretched or broken maybe.

 

You have to take the main sprocket off, to see it, think it's just a split ring holding it on, if my memory serves my right.

 

Worth replacing the sprocket too usually if you need to change clutch IMO.