Stihl MS-250 chainsaw engine bogging down

baymee(LehighValleyPA)April 14, 2008

My neighbor's Stihl chainsaw was bogging down so I said I'd take a look at it. It's not very old.

I took the carb off and dismantled it; blew out the jets, eyeballed everything. Checked the spark arrester, it's like new. Put in new gas mix. Chain spins freely. Adjusting screws at their proper position. Spark plug is new and proper type.

Went to start it up and it ran great. Revved it up and down and it had great high speed and smooth low to high speed acceleration. After about 30 seconds it was bogging down again. It has an external tank vent, and it is working well. Tried restarting and it starts easy enough, but just won't go from low to high speed. If I coax it, I may get it to high speed for one second and then it's bogging again. Tried adjusting the Low speed screw a little, but no good.

Any suggestions appreciated.

Thank you for reporting this comment. Undo
ladylake(minnesota)

Try cleaning the carb again, could be a little crud got back in. Maybe put a new fuel line and filter in first. Steve

    Bookmark   April 14, 2008 at 7:46PM
Thank you for reporting this comment. Undo
masiman(z7 VA)

Fuel and impulse lines can also be problems if they are old and or cracked. Fuel filter and fuel hose are other things to check too. Since you can get some throttling out of it I would not think it is the air filter.

Carb rebuild kits are cheap. The diaphragm could be stiff.

    Bookmark   April 14, 2008 at 8:42PM
Thank you for reporting this comment. Undo
baymee(LehighValleyPA)

Will check again.

    Bookmark   April 15, 2008 at 5:53AM
Thank you for reporting this comment. Undo
rcmoser

I would try to richen up the high mixture alittle see if that helped? If not My guess would be the diaphram also.

    Bookmark   April 15, 2008 at 10:26PM
Thank you for reporting this comment. Undo
baymee(LehighValleyPA)

The diaphragm "appeared" to be good. The high speed jet has a limiter on it, but what is strange is that it ran perfectly for the first 30 seconds after I cleaned the carb. I tried it out again yesterday and it bogged down immediately.

    Bookmark   April 16, 2008 at 6:39AM
Thank you for reporting this comment. Undo
masiman(z7 VA)

To make sure it is not the air filter, try running it briefly with the air filter off.

    Bookmark   April 16, 2008 at 9:09AM
Thank you for reporting this comment. Undo
barbedwire

It seems that all the bases have been covered here. I`ll second the suggestion that you have a good look at the fuel line.

    Bookmark   April 16, 2008 at 9:26AM
Thank you for reporting this comment. Undo
josephtm(CHN India)

This sounds more like a partially blocked pickup body(fuel filter)
Remove the pickup body and try the engine once more.If it runs OK, replace the pickup body.

    Bookmark   April 18, 2008 at 10:13AM
Thank you for reporting this comment. Undo
baymee(LehighValleyPA)

I took the carb apart again, removed and blew out the fuel line and filter, all is clear. Removed the limiter on the high speed needle and tried that adjustment, nothing worked. The fuel line does have some cracks in it, but I applied a little pressure to the line and it doesn't leak through. I hate to tell the guy to get a new line, but that might be the next step.

    Bookmark   April 19, 2008 at 7:06AM
Thank you for reporting this comment. Undo
josephtm(CHN India)

Check the four screws holding the engine pan and cylinder together.
They are located on the underside of the saw.
These screws becoming loose could cause a similar symptom.
External air gets in and causes the engine to lean out.

    Bookmark   April 19, 2008 at 9:46AM
Thank you for reporting this comment. Undo
baymee(LehighValleyPA)

Good point, and will do. But why did it run perfectly for the first 30 seconds after I cleaned the carb internally and then start bogging? Subsequent restarts result in immediate bogging.

    Bookmark   April 20, 2008 at 11:21AM
Thank you for reporting this comment. Undo
ladylake(minnesota)

That running good for 30 seconds is why I suggested to clean the carb again, could have been some dirt in the fuel line or somewhere that clogged it up again. Haveing cleaned the carb again it might be time to try a new fuel line, it could be cracked inside the tank. I suppose you could try holding it upside down, then if the line had a crack in the tank it would suck fuel instead of air. Steve

    Bookmark   April 20, 2008 at 8:56PM
Thank you for reporting this comment. Undo
den69rs96(z6CT)

my older mcCollough would bog down and idle fine. I cleaned the carb. Worked ok for a while, tried adjusting the fuel mixtures and it still bogged. Found cracked fuel lines were the problem.

    Bookmark   April 24, 2008 at 10:51AM
Thank you for reporting this comment. Undo
lawjort_msn_com

I had exactly same problems. Blew out the carb, cleaned air cleaner, new fuel pickup, changed spark plug. Same thing, not working. Changed the fuel pickup line to carb, works like new!

    Bookmark   June 6, 2011 at 8:54AM
Sign Up to comment
More Discussions
Woodzig electric pruner
I have a Woodzig electric pruner and use it often....
ranger_ric
Any owners of the Troy-bilt Cultivator Plus?
I bought this around 1984 and have never seen another...
baymee
Who Makes This 'New' Craftsman 50cc Chain Saw?
Doing a little research on possible replacement saws......
pgtr
New Ryobi S430 engine dies on full throttle
Just bought a new Ryobi straight shaft 4 Cycle S430...
losrubios
Have Chipper/Shredder for trade
I have a very nice gas powered wood chipper/leaf shredder...
charlieboring
Sponsored Products
Dimond Tobermore Ceramic Table Lamp D2236 - D2236
$230.00 | Hayneedle
Besa Milo 4 Pendant 3JC Light with Purple Glass - 3JC-MILO4PL-BR
$382.50 | Hayneedle
DUO 2-Arm Towel Rail by Blomus
$71.99 | Lumens
Engineered Hardwood: Mohawk Flooring Light Amber Maple 3/8 in. Thick x 5 in.
$3.88 | Home Depot
Diz Havana Brown Bronze Tech Lighting Mini Pendant
Euro Style Lighting
LOUNGE Bottle Cooler with Handles by Blomus
$71.09 | Lumens
© 2015 Houzz Inc. Houzz® The new way to design your home™