FIXED - "Warm" start issues - MS250

[spuldup]

Homeowner use (obvs.)
I've had the saw about 12 years, but used it more heavily since heating with wood 2 years ago. It has never had the typical hard to start complaints, either cold or hot (3 pulls to bark cold, runs immediately hot). But if I run it for a while and get up to temp, and shut it off for 5-20 minutes, it will not start. I have tried choking it, not choking it, pulling the plug to clear gas... But no matter what, the only way to get it to start is to wait to cool (I usually just grab another saw if at home). Hot restarts (off less than 4-5 minutes) are no problem for it.

It has a straight thru muffler and I shaped the intake and exhaust ports (not ported). Issue existed before these mods. Carb limiters removed, and I tune it every day of use. It will idle forever and run in any position just fine. I rebuilt the carb - same problem. It is running an 18" bar with .325 pico chain. For such a small saw it's power is quite impressive for cleanup work and I can run it all day due to the low weight.

Hopefully I've provided enough info for you guys to weigh in. Thanks in advance!

 

[skooter]

Homeowner use (obvs.)
I've had the saw about 12 years, but used it more heavily since heating with wood 2 years ago. It has never had the typical hard to start complaints, either cold or hot (3 pulls to bark cold, runs immediately hot). But if I run it for a while and get up to temp, and shut it off for 5-20 minutes, it will not start. I have tried choking it, not choking it, pulling the plug to clear gas... But no matter what, the only way to get it to start is to wait to cool (I usually just grab another saw if at home). Hot restarts (off less than 4-5 minutes) are no problem for it.

It has a straight thru muffler and I shaped the intake and exhaust ports (not ported). Issue existed before these mods. Carb limiters removed, and I tune it every day of use. It will idle forever and run in any position just fine. I rebuilt the carb - same problem. It is running an 18" bar with .325 pico chain. For such a small saw it's power is quite impressive for cleanup work and I can run it all day due to the low weight.

Hopefully I've provided enough info for you guys to weigh in. Thanks in advance!

One simple thing to try is a new spark plug

 

[coffeebrk]

Have you checked for spark when it doesn't start?

 

[spuldup]

Yes I have tried a new NGK plug. Same issue. Never checked the spark quality in this warm condition. @coffeebrk Are you thinking there is a "dead band" of temperature in the coil? Or something else?

 

[lwmibc]

How old is the gas and is there methanol in it? I had a similar problem with my favourite firewood saw, even bought a new Chinese replacement in case the old Dolmar was finally quitting; wouldn't restart once hot on a hot day.

Turned out the new saw exhibited the same thing--upon which I realize the gas I was using had been bought the summer before. My interpretation was that the gas was boiling in the carb and fuel line close to it when shut off hot, and I had to pull and pull until it pumped liquid fuel into the carb again. Gasoline isn't what it used to be.

Bought fresh gas, still the methanol-containing low grade, and problem disappeared on both saw. Possible?

 

[cscltd]

Have you tried-
1 pull (only) on full choke, then put it on fast idle position and then pull again.
I find that works

 

[lwmibc]

I'm 75 years old, no newly to chainsaws. If there's no liquid fuel for several inches of fuel line due to boiling, that can't/won't work.

I'd always been able to eventually get the saw to run, but it takes a lot of pulling to get the liquid fuel filling the line and fuel pump/metering sides of the carb to the point where it can do its job.

Fresh fuel eliminated the problem, on both saws. I don't mind if anyone disagrees, only trying to help by description of my experience. I hope it helps; after all, just trying fresh fuel during hot weather is not hard to do. I even saved the old fuel and mixed it with fresh mix when the weather cooled down. It works fine.

 

[Hulpio]

If it starts normally when you let is cool I would suggest too rich idle mixture. Have you ever tried to start full throttle?

 

[stihltech]

#1 check the spark when it does not start hot. Open the fuel cap and try it if the spark is good. The poor man's vac and pressure test with spray brake clean (using the straw) is a very good idea. I put a lot of carburetors on saws of this age.

 

[Lawless]

250s are known for this. I hated mine for the same reasons. I put an aftermarket Chinese carb on it and it is 100% reliable and a great saw now. It is my ATV saw and never fails to start in any condition. I don’t know what in the factory carb causes this, but rebuilding doesn't fix it.

https://www.amazon.com/gp/product/B06XWHHGHH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[spuldup]

@lwmibc New ethanol free gas, 90 octane, also stabil 360 in it, echo red armor at 40:1.
@cscltd Not remembering specifically, I likely have due to the number of attempts, but will purposefully try next time
@Hulpio leaning out the idle more than it is kills throttle response, but I can try a small bump.
@stihltech Good idea to check the spark at that time. It is strong when cold (the only tie I've checked it). Tank breather is working. There is no shortage of fuel, so the ignition is def. suspect.
@Lawless I clicked your link and realized I bought that exact carb years ago for it, lol! That time was because wanted one w/o limiters. I still had this issue with that one, so I rebuilt it with an OEM kit. I had forgotten that I swapped the carb back then.

Thanks to all for the replies. I've got a few new things to try now. Sadly it's raining all weekend...

 

[coffeebrk]

Have you checked for spark when it doesn't start?

#1 check the spark when it does not start hot. Open the fuel cap and try it if the spark is good. The poor man's vac and pressure test with spray brake clean (using the straw) is a very good idea. I put a lot of carburetors on saws of this age.

Why I bother, lol

 

[Hulpio]

Leaning idle mix wont help then. It did not have much chance even in the beginning. There is a reason for your problems.

 

[SteveSr]

@stihltech Good idea to check the spark at that time. It is strong when cold (the only tie I've checked it). Tank breather is working. There is no shortage of fuel, so the ignition is def. suspect.

Coils are known to fail hot as in after heat soaking. The only way to determine for sure is to exchange coils. Should be lots of used ones on Ebay.

You can also try letting it idle for 30-60 seconds to cool off before shutting it down.

 

[spuldup]

@Hulpio Can you elaborate on this cryptic language?
@SteveSr I do "idle down" all my equipment when possible. I'm not a fan of the parts cannon approach. But given the age, a new coil may be on the docket.

 

[SteveSr]

@SteveSr I do "idle down" all my equipment when possible. I'm not a fan of the parts cannon approach. But given the age, a new coil may be on the docket.

Used Ebay come with a 30 day satisfaction guarantee!

 

[Pioneer]

Had that problem this spring with winter gas, one of my saws would not start again until it cooled down. New gas cured the problem.

 

[Hulpio]

@Hulpio Can you elaborate on this cryptic language?
@SteveSr I do "idle down" all my equipment when possible. I'm not a fan of the parts cannon approach. But given the age, a new coil may be on the docket.

If leaning the idle mix kills throttle response then it is not too rich in the beginning. There is something else.

 

[slowcar281]

I’ve seen coils that would fail occasionally when hot. Next time it acts up check for spark using an actual spark tester, rather than grounding the spark plug itself.

I know you said the tank breather works fine but try cracking the fuel cap next time it acts up if you have a good spark. I had a mower that would vapor lock because of poor venting.

 

[spuldup]

Ok well I feel stupid now. I ordered a new coil, went to replace it, and saw the factory coil was caked with oily sawdust. I simply cleaned that off and sanded the flywheel magnents a bit. Put it back together and tried the warm start thing. Worked 5/5 times.

Kind of odd that it didn't have issues starting cold or hot, but there you go.