MS250

[Opihi59]

A friend brought me his trusted MS250 and told me it quit running and he was unable to get it to start. Not like I'm an expert, but he knows I've fixed 2-strokes in the past. I found it did not make spark, so installed a new Amazon coil. After this it did run fine. I felt it was fixed, and it also started easily and ran the next day for me, but when he came to pick it up, I was unable to get it to run again, not even to pop. I've pulled apart the carb, and there is no gunk in it, the diaphragm is soft and moves well. It has spark and compression. I am really unsure what it is I am missing. It has new fuel line, new filter, new spark plug and did run fine. I'm not really sure what to consider next and feel I am missing something reasonably simple so I'm happy to consider recommendations on where to look next.
I have read thru PAGES of MS250 posts, and do not feel I've come up with too much helpful: I've looked at the piston, there is no scoring, and the compression feels good. The exhaust screen isn't plugged, and yes, it ran fine once I put in a new coil. I still have spark. Thanks in advance of course.
Provided the attachment works, this is it running immediately after I put in the new aftermarket coil.

 

[cookies]

I would not trust that amazon coil, when you try to start it pull the plug and see if its wet with fuel.

 

[Opihi59]

Well, it beats spending $100 on an OEM coil, IF I could find one. It makes spark, and it ran with it when it would not spark w the original OEM coil. The sparkplug does get wet with fuel, though in addition to this I have also tried priming with a small douche of gas down the sparkplug hole.

 

[cookies]

Is it the older rectangle coil or the rounded universal version? either version of coil used oem can be had for under 30 bucks. Inspect the flywheel magnets strength and for correct polarity, coil gap and even the flywheels key being stripped. I'm betting that coil shlt the bed or the plug is after one use from getting warm or the plug is bad. Nothing magical happened since you repaired it, a low fuel level in the tank sometimes gets me thinking there is a carb issue haha
In the last year I have experienced amazons knockoff chinese parts have been around a 80% bad out of the box or suffer a immediate failure vs just a year and a half ago being about 25%. I really think it is a concentrated sabotage on us. For a decade I was the guy championing the under 20 dollar carbs off amazon and ebay but this past year changed that after dozens of issues. If I buy aftermarket I get it from one of the usual saw websites like hl supply, sawzilla, dukes etc.

 

[L34]

Might not be sparking under compression.

 

[allbrandfan]

I'd start with making sure it's not simply flooded. A "douche" in the sparkplug hole is pretty much guaranteed to flood and if you are using the choke, it just gets worse from there. If plug is wet it may not spark. Weak coil, wet plug, bad timing (key) all might increase sensitivity to over-rich starting conditions. Yesterday may have been a lucky start and today she's too rich. I'd reset the needles to baseline, hold throttle wide open and rope it about 6x then begin the start procedure (choke on1-2 pulls, half choke etc).

If you have spark and can't fire, a TINY spritz of gumout or ether can confirm whether it's a fuel shortage. Neither contain lube so I wouldn't try to run on spray but if it will pop on spray and not without then you likely have a carb problem. At 45cc, this isn't a SBC and squirting any more than a drip of fuel into whatever orifice is gonna drown it.

 

[ZeroJunk]

I'd start with making sure it's not simply flooded

^^^^

Put it on high idle, no choke, and pull it 20 or 30 times. Bet she'll take off.

 

[Kenh]

I was a Stihl certified tech in a former lifetime. I've forgotten most of what I knew. But often a spark plug that sparks on the open air will not spark under compression. Try a new plug. Set the flywheel to coil gap set to .010" Also if you just want to see if you have a viable engine, squirt some brake parts cleaner down the plug hole. DO NOT USE THE CHLORINATED VERSION. That makes phosgene gas which can kill you. The brake cleaner is far less likely to flood the engine.
I agree that the import parts quality has gone in the $hitter lately.

Ken

 

[Chevboy0167]

Husqy 55 came to the bench with brand new coil from the usual scumbags. Perfect blue/white spark outside cylinder. Under compression was NFG.

10 dollar used OEM Husqvarna coil from eBay and it ran better than the shinny red super stock Dodge that the little old lady from Pasadena drove!

 

[Wood Doctor]

^^^^

Put it on high idle, no choke, and pull it 20 or 30 times. Bet she'll take off.

Or just let it sit for half an hour and run a backup saw to keep working. No need to choke it on the restart, just set it on fast idle. That has worked for me many times.

 

[Oletrapper]

^^^^

Put it on high idle, no choke, and pull it 20 or 30 times. Bet she'll take off.

Zero Junk be correct. I've probably said it a hundred times. The MS 250 is the easiest saw to flood I have ever seen. My starting method is full choke and pull twice, then half choke and pull till it starts. If all else fails, pull the spark plug and let it set for a few days. jmho OT

 

[2StrokeFondler]

Husqy 55 came to the bench with brand new coil from the usual scumbags. Perfect blue/white spark outside cylinder. Under compression was NFG.

10 dollar used OEM Husqvarna coil from eBay and it ran better than the shinny red super stock Dodge that the little old lady from Pasadena drove!


View attachment 1242704 View attachment 1242705

Did you measure the coils?

 

[Okie]

Put a OEM new mag and correct type spark plug on the saw.
(and set the air gaps to correct specs)

Why throw China junk on something the other guy is paying for and wants you to fix correctly?

It will most likely run ok afterwards if you got the carb back together correctly.

If it don't run correctly afterwards fess up and tell him it need to go to the Stihl EXPERT repair shop. (from reading your first post)

 

[Opihi59]

Thank you all for your input.
It actually is acting like there is an OFF switch, and switched to the OFF position if that makes any sense at all.
I wonder if there is an acceptable way to test a coil that is available to the average person, other than swapping it in, and looking for a spark. I'm not sure what it is that I am missing here. Attached are photos of the OEM coil (sitting on the flywheel) and the aftermarket coil installed. Hopefully to answer @cookies question.
I have tried SEVERAL new spark plugs of course. Right now I am working on a question of spark timing and the keyway issue and need to pull the flywheel. it is VERY tight, and now I cannot recall if these flywheel bolts on the early Stihls were LEFT hand thread, or RIGHT hand. I don't want to brute this thing up quite honestly.
I have tried one by one everyone's starting suggestions, one at a time over a several day period as they have come in. No luck here. I'll let everyone know about spark timing once I get the flywheel off, which seems to be posing a challenge.

EDIT--I have NOT tried any alternative starting fluids as of yet.

 

[ZeroJunk]

Thank you all for your input.
It actually is acting like there is an OFF switch, and switched to the OFF position if that makes any sense at all.
I wonder if there is an acceptable way to test a coil that is available to the average person, other than swapping it in, and looking for a spark. I'm not sure what it is that I am missing here. Attached are photos of the OEM coil (sitting on the flywheel) and the aftermarket coil installed. Hopefully to answer @cookies question.
I have tried SEVERAL new spark plugs of course. Right now I am working on a question of spark timing and the keyway issue and need to pull the flywheel. it is VERY tight, and now I cannot recall if these flywheel bolts on the early Stihls were LEFT hand thread, or RIGHT hand. I don't want to brute this thing up quite honestly.
I have tried one by one everyone's starting suggestions, one at a time over a several day period as they have come in. No luck here. I'll let everyone know about spark timing once I get the flywheel off, which seems to be posing a challenge.

EDIT--I have NOT tried any alternative starting fluids as of yet.

The flywheel is standard righty tightie lefty loosey. But, it is on a taper. So, if you want to get it off you need to screw the nut out and while holding the flywheel with large channel locks put a deep socket against the flange of the nut and hit it with a hammer holding the saw up by the channel locks.

We do see flywheels move, but you would have needed to be running high RPM and the chain brake or something lock the chain to spin it.

 

[Chevboy0167]

Did you measure the coils?

No. Modern solid-state coils have transistors, capacitors, resistors and induction triggers that cannot be tested individually for fault finding.

Old school (and cool!) points systems can be tested as the components are individually packaged, Also mechanically actuated so as us humans can use our digits to manipulate them from on/off state.

Video is a bit long and somewhat confusing to some but is spot on.

 

[allbrandfan]

Thank you all for your input.
It actually is acting like there is an OFF switch, and switched to the OFF position if that makes any sense at all.
I wonder if there is an acceptable way to test a coil that is available to the average person, other than swapping it in, and looking for a spark. I'm not sure what it is that I am missing here. Attached are photos of the OEM coil (sitting on the flywheel) and the aftermarket coil installed. Hopefully to answer @cookies question.
I have tried SEVERAL new spark plugs of course. Right now I am working on a question of spark timing and the keyway issue and need to pull the flywheel. it is VERY tight, and now I cannot recall if these flywheel bolts on the early Stihls were LEFT hand thread, or RIGHT hand. I don't want to brute this thing up quite honestly.
I have tried one by one everyone's starting suggestions, one at a time over a several day period as they have come in. No luck here. I'll let everyone know about spark timing once I get the flywheel off, which seems to be posing a challenge.

EDIT--I have NOT tried any alternative starting fluids as of yet.

Surely you've examined the kill switch and nothing is amiss there? To be clear, it has spark but the timing or strength is suspect, or does it have no spark whatsoever?

 

[Opihi59]

Surely you've examined the kill switch and nothing is amiss there? To be clear, it has spark but the timing or strength is suspect, or does it have no spark whatsoever?

Yeah. It has spark, it RAN after I changed the coil, it ran again the next day as well, but when my buddy came to get it, it would not run.

Interesting about the kill switch. I started checking continuity of the wires. I found all the wires to be intact, but found very puzzling thing in that there was continuity between the kill part of the switch, with the kill tab, when the saw was in choke and run position. I know this may sound sketchy and can post up some poser photos of the situation but it is as follows: There is a wire from the coil to the tab on the switch. When the saw is in choke, half choke and run positions, the ground wire and the tab do not touch. There is not supposed to be continuity until the run lever is flipped all the way up. At this point, continuity is established and the saw quits running. However in my saw,even though these two parts-tab and ground wire are not touching in any way, there is electrical continuity between them when testing with a meter. I have pulled all wires, and found no shorts, no exposed conductors. I can find no reason for the continuity. Tomorrow I'll try disconnecting wires at the kill switch end and taping them, and see if it will then run, but I'm going to fiddle with the flywheel first and rule that out as a problem. Things here simply not making any sense at all.

 

[GMB74]

What you have stated above is correct. You are testing for continuity from the coil ground wire at the shutoff switch back through the coil to ground. This is normal.

It sounds to me like you have either a badly flooded engine or a faulty aftermarket coil.

 

[Opihi59]

What you have stated above is correct. You are testing for continuity from the coil ground wire at the shutoff switch back through the coil to ground. This is normal.

It sounds to me like you have either a badly flooded engine or a faulty aftermarket coil.

Well, now that begs the question of how the OFF switch is actually working on an intact saw. If there is continuity whether the switch is open or closed, then how is that supposed to be working? Obviously I'm missing something here. Willing to hear more on this of course. Thank you for your input and interest in my thread.