Idles too fast - Stihl MS-250

[HarleyT]

When I said metering valve I meant the fulcrum that controls fuel flow. 2X now I have had an otherwise good saw that wouldn't take a tune and it turned out the thing was bent wrong allowing to much fuel.

You then mean "metering lever".

 

[philo]

I am pleased to report that I have found and fixed the problem, which of course had nothing to do with the clutch or clutch springs which someone had suggested. The problem was, as I suspected(and others too) an air leak, and since I had already replaced the fuel line and impulse line(but not the rubber boot inbetween the cylinder and the carburetor), let alone rebuild the carburetor with a new kit, what fixed it was replacing the crankshaft seals. The aha moment came when, while disassembling the saw I finally got to the four screws that hold the engine clamshell together underneath the saw. The two screws that are hidden underneath the grip handle bar were loose! The other two were tight - the ones that you can easily get at if you flip the saw over. How they got loose is a mystery, though I have used the saw hard for the last 6 years. And so the loose screws probably caused some wobble in the crankshaft which wore out the crankshaft seals prematurely. The crankshaft bearings, cylinder bore and cylinder/rings were all fine.

I would suggest to any MS-250 owner that they take the handle off their saws and check the tightness of these two screws periodically.

The saw now idles and runs perfectly, just as it did when it was new. Disassembly of the saw was greatly aided by the YouTube videos that show and explain the disassembly process pretty thoroughly. It's not an easy repair, but anyone who is reasonably handy could do it. The seals were $4 on eBay and the hoses and carb kits brought the parts cost up to about $20. I never did a compression/vacuum test - I don't have the tools for that - but if your 250(or similar) has an unstable or a fast idle even after a carb cleaning and rebuild, then the problem is almost certainly an air leak, and there are only a few places where leaks of this sort can take place. I used Permatex Ultra Black RTV to seal the engine clamshell as suggested in the YouTube videos. These MS-250s are great saws and well worth the trouble to fix them, even when it requires a full engine breakdown.

 

[Chainsaw Jim]

Everyone fix my saw right now and you had better not give me the wrong troubleshooting tip!

 

[HarleyT]

which of course had nothing to do with the clutch or clutch springs which someone had suggested.

Yeah, that guy is a well known idiot!!!