I just bought this MS 250 about two weeks ago, did some break-in time on it, and cut up a couple of small trees. Running just fine. Took it out again two days ago and it refused to start. Went to pull the factory spark plug to check it out, and found it so dang tight that a breaker bar was needed to break it free. Didn't check the gap, but did determine that there was spark. Not wanting to dig into it any further since it was just purchased, I took it back to the small engine dealer I bought it from. Fella took it to the back room for a few, and returned with the problem fixed. The spark plug gap had somehow closed down to the point that it wouldn't run. NOW... How did that happen? I figured that the only way possible is that the piston had made contact with the electrode. It ran fine before, and I told him that. He said there's no way that the piston could have hit the spark plug. So, anybody have a possible explanation? The clearance between the piston and the plug is between .02 and .03 MM according to the information I could find. Thats darn close as it is. Something closed the gap on that spark plug is all I know. But what?
New MS 250 PROBLEM!
- Thread starter LawrenceK
- Start date
Yeah, the piston shouldn't normally hit the plug..
Maybe they're not quite seated right, or there could have been a tiny manufacturing defect in the plug itself that allowed the electrode to bend in?
But glad that the dealer fixed it quickly!
Hopefully, it was just a fluke with that specific plug!
Maybe they're not quite seated right, or there could have been a tiny manufacturing defect in the plug itself that allowed the electrode to bend in?
But glad that the dealer fixed it quickly!
Hopefully, it was just a fluke with that specific plug!
xSourMilk23
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Doug Balko
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Sounds to me like the spark plug was WAY overtightened at the factory and the plug was indeed being hit by the piston!
Leon Couper
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This is the right plug for it NGK BPMR7A which you probably have in it.
Strange one to me never heard of it happening but suppose there is always
a first time. Bit like the other guys maybe over tightening could have caused it
it is not a good habit to get into they don't have to be that tight.
Strange one to me never heard of it happening but suppose there is always
a first time. Bit like the other guys maybe over tightening could have caused it
it is not a good habit to get into they don't have to be that tight.
Rickochet
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- Aug 31, 2025
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I've been working on engines of all kinds for many, many years and have never seen a spark plug over-tightened enough to affect the gap.
#1..... Me being a non-perfect human being, I have dropped a spark plug (or 2) and smacked at least one plug on the cylinder head during installation, which tightened up the gap. Never to the point of complete closure, but enough for me to notice it and regap before proceeding. It's easy to overlook the little things like that when you're cutting teeth on working on engines. Do you think you may have possibly dropped it or smacked it enough to close the gap just prior to reinstallation?
#2.... If the plug was incorrectly gapped completely closed up from the manufacturer, there would not be any spark to allow it to run. However, if it was almost completely closed when new, and was running very rich and/or too much oil was in the gas/oil mixture, there's a slim chance the plug was fouled enough during your break-in period and the fouling solidified enough to prevent a spark from occurring.
#3.... Mother Nature just didn't like seeing you cutting down her precious trees and she placed a negative mojo on the plug.
Whichever one it is, if you ever encounter a similar situation, take photos of the plug so we can provide a proper inspection and offer advice. I hope you enjoy many years of cutting wood to stay warm as I have!
#1..... Me being a non-perfect human being, I have dropped a spark plug (or 2) and smacked at least one plug on the cylinder head during installation, which tightened up the gap. Never to the point of complete closure, but enough for me to notice it and regap before proceeding. It's easy to overlook the little things like that when you're cutting teeth on working on engines. Do you think you may have possibly dropped it or smacked it enough to close the gap just prior to reinstallation?
#2.... If the plug was incorrectly gapped completely closed up from the manufacturer, there would not be any spark to allow it to run. However, if it was almost completely closed when new, and was running very rich and/or too much oil was in the gas/oil mixture, there's a slim chance the plug was fouled enough during your break-in period and the fouling solidified enough to prevent a spark from occurring.
#3.... Mother Nature just didn't like seeing you cutting down her precious trees and she placed a negative mojo on the plug.
Whichever one it is, if you ever encounter a similar situation, take photos of the plug so we can provide a proper inspection and offer advice. I hope you enjoy many years of cutting wood to stay warm as I have!
