Thoughts on an MS 250

[TreePointer]

Difficult restart when hot has meant a couple things in my experience (I'm not a pro service tech, just a farm tinkerer):

1. Vapor lock. Crack open fuel cap immediately after turning off saw to relieve low pressure condition. Eventually replace fuel tank breather valve.

2. Low carburetor jet is too lean. Turn out "L" screw. Sometimes as little as 1/8 turn can solve this issue.

I've read about other issues but I've never had them with my chainsaws. I did have to replace an ignition module in a lawnmower (not a 2-cycle engine) that was causing difficult restarts with a hot engine. Spark plugs at the end of their life can also cause issues with hot engines, bit mine get changed before they get too old.

 

[WeldrDave]

Any thoughts on what could be the problem?

I'm not a Mechanic, but I had a magneto do that before, it had a crack in it. This wasn't a chainsaw, it was an outboard but basicly same thing.
Master Mech I'm sure can help

 

[MasterMech]

Ignition is worth a shot. I would make sure the fuel tank vent works properly, try cracking the gas cap after you shut it down and just before you restart. If that doesn't change anything then I would look into ignition trouble. Ignition problems eventually worsen to the point of the saw shutting down while in use.

 

[Angelo C]

Ignition is worth a shot. I would make sure the fuel tank vent works properly, try cracking the gas cap after you shut it down and just before you restart. If that doesn't change anything then I would look into ignition trouble. Ignition problems eventually worsen to the point of the saw shutting down while in use.

Im with Mech on this one...check the spark cold once and see what it looks like. then run it for a while and see if the saw fails, then check the coil again once it wont start.
not to seem stupid but is your "restart" method the same as your "cold start" ??? you are not using the choke again once its warm are you.?
sorry had to ask.

 

[Tony D]

Nope... no choking involved. I will do some trouble shooting this weekend and let you guys know what i find. Thanks again for the input!

 

[Tony D]

I was doing some cutting yesterday and since i was prepared to do some trouble shooting to the 357 it ran like a top. I cut down an 18" standing dead hard maple, cut it up and then turned the saw off. Then drove about 10 minutes away and went to fire the saw up expecting it to at least give me a little grief, but it fired right up. I cut for another 15 minutes and then shut it off again. Let it sit for another 10 and went to start it again and it fired right up. I did crack the gas cap before the second start up to see if i could hear a sucking sound caused by vapor lock but didn't hear anything. I hope this behavior continues because that saw rips when its running good with a sharp chain!

 

[schwaggly]

I just bartered my MS 250 for a Craftsman 4-1 chipper vacuum. Now I'm looking for a simple and strong 18 inch saw that can take a full chisel chain.

 

[Angelo C]

I was doing some cutting yesterday and since i was prepared to do some trouble shooting to the 357 it ran like a top. I cut down an 18" standing dead hard maple, cut it up and then turned the saw off. Then drove about 10 minutes away and went to fire the saw up expecting it to at least give me a little grief, but it fired right up. I cut for another 15 minutes and then shut it off again. Let it sit for another 10 and went to start it again and it fired right up. I did crack the gas cap before the second start up to see if i could hear a sucking sound caused by vapor lock but didn't hear anything. I hope this behavior continues because that saw rips when its running good with a sharp chain!

Tony,
sometimes changing the Mix/fuel/ratio or any of the above can slightly alter the carb settings, Im thinking that might be a contributor, but a faulty ignition will diagnose intermittently like you are experiencing.