Siezed chainsaw

[StephenOak]

I have found that my chainsaw, a Stihl MS171, once I have started it with the choke on it will always die when I start to run the throttle, which automatically takes the choke off.

I think this is because it is not warm internally, it lives in a cold garage, because once it has warmed up it runs fine and will restart and run fine.

So I have got into the, probably bad, habit of starting it and then letting it run with the choke on for a couple of minutes. Thus far that has worked okay, it runs when I rev the throttle.

A few days ago I left it running with the choke on for a bit longer than usual and it just died. When I tried to restart it, I could not pull the starter cable and the chain would not run on the drive sprocket.

I have removed the cover that contains the starter assembly, that moves okay detached from the machine.

Inside that is something that looks a bit like an impeller. That will turn by hand and it seems like the internals are moving, resistance on that 'impeller' increases and then suddenly drops, when that happens there is a sound of something moving and the shaft of the drive sprocket seems to move.

I cleaned out a reasonable amount of muck and re-attached the starter assembly cover but it is no better than before.

Is there anything straightforward I can do to sort this out?

If not there is a good shop / service place near me and I will take it there.

 

[Burnerman]

The MS171 is a great, high revving small saw
The choke is only used to start up.....once the saw has fired, take the choke off and start up on full throttle - allow it to rev until it can tickover without stalling. Don't worry about lubrication issues - there is enough oil there.
Continued use of the choke will cause the engine to fill up with unburnt fuel which may cause difficult restarting. If this happens, pull the plug out, turn the saw upside down and pull the recoil starter briskly. You'll get a spray of fuel out of the spark plug hole.
The impeller is the cooling fan and flywheel. In the centre is the mechanism that catches the dog when you pull the recoil starter cord. The cooling fan (flywheel) should not turn freely....once per revolution the resistance will become high as the piston reaches the top of its stroke and its compression that you feel - all completely normal and desirable! No compression means a knackered motor.
So, take the spark plug out, crank the engine with the starter and blow the excess fuel out. Normal service will be resumed!
John

 

[StephenOak]

John, I was hoping you would be along soon!

So, take the spark plug out, crank the engine with the starter and blow the excess fuel out. Normal service will be resumed!

Thanks, you are a star. I just did that and the starter cord will now pull freely.

I could not get it to start after maybe 20 tries. That is worse than normal but not much. It always takes me a dozen or more goes to get it to start.

I have put it somewhere warmer and will try again in the morning.

The choke is only used to start up.....once the saw has fired, take the choke off and start up on full throttle

And it always dies. Then it takes me another dozen or more goes to get it to start again. That is why I have been keeping the choke on until it warms up.

Does being so hard to start sound like I am doing something wrong or a fault with the machine?

 

[Burnerman]

Hi Stephen
I very much doubt there is anything wrong with your saw, but obviously I haven't seen it! Anyway, when these things come to me, this is what I do. With any small two stroke machine, you have to show it who is BOSS.
(1) Squeeze the throttle trigger, hold and set the lever on the left to full choke. Release your hold on the trigger - this should hold the machine on full choke and full throttle. Touching the throttle trigger here will take the choke off and it won't go.
(2) Take the chain brake OFF.
(3) Trap the machine on the ground with your right boot heel on the handle.
(4) Pull the recoil starter rope very quickly - maybe three pulls in one second!
Within 5 pulls, the machine will 'pop' or maybe even run for a short time. At that point:
Move the left lever one click down, so the choke is off but the machine is still on full throttle. Don't touch the throttle trigger!
Within a couple of more swift pulls, the saw should scream into life. You can now squeeze the throttle trigger to allow the saw to speed up and slow down.....keep doing this for maybe 20 sec until the engine will tick over on its own.
(If the engine stalls here, put (1) into practice again - but only give it 1 pull to prevent flooding).
Its best to start a two stroke on full throttle - warm or cold. Familiarity will allow you to start it without throttle.
Hope this helps!
Regards
John

 

[StephenOak]

(1) Squeeze the throttle trigger, hold and set the lever on the left to full choke.

The lever on the left has four settings, from top to bottom:
- Off
- Run
- Warm weather choke
- Cold weather choke

I use the chainsaw a lot more in the winter so I normally use the cold weather choke setting.

Release your hold on the trigger - this should hold the machine on full choke and full throttle.

The throttle control is spring-loaded so when I release it, it goes to zero throttle.

(4) Pull the recoil starter rope very quickly - maybe three pulls in one second!

That is quite different to what I was doing! I was getting the starter engaged with no slack and giving one hard pull.

I just tried it using your method and I got it started after five or six goes. It did stall when I put the throttle on but I was able to restart it quite quickly and was able to do the speed up and slow down process to get it running on tick over.

With hindsight this is obvious. Multiple pulls close together will have the flywheel still moving and so better able to start the motor.

I did all of this with the chain off. I re-attached the chain and restarted it, to make sure that it was fully working okay. On tick over with the chain brake off the chain was creeping around. When I reved it and then took the throttle off the chain was moving at a reasonable rate. So I looked in the manual and it seemed like the carburetor needed to be adjusted. I did that (following the instructions w/o really knowing what I was doing!) and it seems fine now.

Thanks very much for all your help.

 

[Burnerman]

Thanks for the feedback Stephen, for sure, you are getting there!
I think the lever on the left has these settings - mind you I don't have any handbooks or manuals so I don't know what Stihl calls it!
Off
Run
Full throttle - no choke
Full throttle - full choke.

So, for cold starts, its full throttle full choke position, any other time its full throttle . Usually I just squeeze the throttle lever and keep it open full when I'm cranking the thing over - so long as its on the run position of course!

If the chain is moving on tickover, the tickover speed is too high. A screw marked LA adjusts this mechanically. I don't know what LA stands for! You've discovered this anyway.

Masterclass:
These saws can suffer from oil starvation to the chain bar. Occasionally check to see that oil is delivering - you can see the oil being delivered through a hole with the chain bar off. The oil pumps don't usually fail, they gum up and can be freed by bleeding diesel through the oiling system.

Keep the air cleaner spotlessly clean.

Its worth getting a spare spark plug - BPMR7A if its the larger NGK one.

Use Aspen two stroke fuel if the saw is only used a couple of times a year.

Keep a spare chain handy - one excursion into soil blunts it in seconds

Cheers and be safe!
John

 

[StephenOak]

Sorry for the long delay in responding, I've been very busy and have not looked here for days. Thanks very much for all your help.

Use Aspen two stroke fuel if the saw is only used a couple of times a year.

We had a discussion about this before
https://www.diynot.com/diy/threads/fuel-for-a-chainsaw-or-any-two-stroke-for-that-matter.494053/

I still have the last of that fuel but when it is gone I will get some Aspen or Stihl.

Keep a spare chain handy - one excursion into soil blunts it in seconds

Oh indeed! A couple off years ago I had cut down / cut back some trees, cut them into convenient lengths and taken them to the saw-horse. I was cutting one piece into firewood pieces when there were some sparks and the chain (the only one I had) was blunt. I think that there must have been some wire around the tree when it was small and it grew around the wire. So I ditched that length of wood.

A day or so later I returned to this having bought two new chains and a sharpening kit. Some time into cutting again there were some sparks and a new chain was blunt. It was a different length from the same tree.