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!