Please Help! Chainsaw bogs and dies when revs

I used my Stihl ms260 last weekend and worked great. The saw is 5 years old and been trouble free, still on original spark plug and been using Stihl synthetic 2 cycle oil. Went to cut wood tonight and it was hard to start and seemed to idle fine (perhaps faster than normal) but when I went to rev it to cut the motor would bog and die. I did run last years gas last wknd, but dumped it and made fresh today. Borrowed a new plug fro my dads saw and tried it with same result. Air filter is clean. Seems lime maybe a jetting problem? I'm gonna pick up new plug tomorrow. Any thoughts, ideas, suggestions or similar experiences? Thanks

 

sounds silly but is the choke still on?

 

Are you sure you mixed the fuel/oil right?

 

I had the same trouble with my 2 cycle weed eater. My dad used to be a small engine mechanic and gave me a suggestion. He said I should take the muffler apart and see if it was clogged up with carbon. There is probably a little screen in there that has carbon buildup on it. If that is the case you can burn it off with a torch. Or you can just remove the screen. That was my problem and this worked for me, so good luck!

 

The screen is a spark arrestor. Manditory in California because of wild fires, now I beleive they are everywhere, good idea to clean it, also check the brake on the blade, I know basic but start easy, I just went through this, my saw would run fine then as soon as I hit the gas, blah... nothing. I took old gas out, added some sta-bil gas treatment to new gas finally got it to run normal. I think the problem is ethanol in gas, espesially gas that sits for a while. I read somewhere they want you to drain gas after every use. Pain in the ass. SO i use gas additive in all my 2 stroke gas mixture, either sta-bil, lucas, hell even sea foam says it will keep 2 stroke gas good for a long time. Poin is get it running add the snake oil, and dont let it gum up . Hope this helps. Kevin

 

Both good suggestions, 2 strokes can be real finicky at times, sounds like maybe running a little lean, did you pull the newer plug & look at it to see how its burning ? If it looks "too clean" , I'd try adjusting the air/fuel mix screw, your statement about it "idling a bit faster than normal" leads me to think its running lean, good luck !!

 

Gas loses most of is oomph after three months. Stabilizer will keep the varnish away, but won't stop the gas from evaporating. No matter how tight the seal on the tank is, replace the gas every three months and use stabilizer. The stihl oil from the dealer will have stabilizer already in it, they will usually tune it for you for free (only if you bought it there)
I assume you checked/cleaned your air filter.

 

In my Stihl's I found that I had to use mid or hitest gas mix, even the manual says that. Hopefully your using fresh fuel mix too, the stabilizers do work wonders,I use SeaFoam in the outboards, garden tractors, and motorcycle. Seems my fuel problems have damn near been eradicated.

 

i had the "clunk" (fuel pickup) get clogged on my Dolmar. check to make sure the "clunk" isnt plugged and the hose has no leaks... also, doublecheck all the fuel lines for leaks.

 

Thanks for the help guys. I've tried all those things except running gas treatments through. The gas I ran last weekend probably gummed up the carb and I'm gonna have to take it somewhere to get it cleaned and rebuilt. Still having problem after new plug, but acts like its running too rich. Lots of black goo spewing out exhaust. I've tried adjusting low speed screw and to no avail.
Removing the carb looks like a major PITA.

 

Change fuel filter. Carb settings should not be changed if it ran fine when you put it up. Change out fuel, disassemble carb and clean jets with a small drill bit or torch tip cleaner. New plug prolly wouldn't hurt either. Reassemble, fresh fuel...should be good to go.

 

Too much oil, And needs new spark plug. How dull is the chain

 

don't mess with the jets/air fuel mixture too much. you can adjust the idle a little but I would'nt mess with the highs and lows. sounds like you got shitty fuel. What did you mix your gas at?? What did the plug look like when you took it it out?

Check for holes in the rubber hose/boot that goes from the carb to the cylinder? Is the chain spinning at an idle? Does the clutch look normal? all springs in tact, everything look fine?

 

this. x2

 

i was having a starting/running prob with my troybilt weedeater a few weeks back. i cleaned the foam filter behind the breather/before the carb and also sprayed some pb blaster small engine tune up stuff into the carb and let it sit for a couple hours. apparently, as hot as it had gotten in my garage....the gas that was still in the carb had kinda gelled up, but the pb blaster stuff melted it down real good. fires right up now.

 

Thanks for all your input guys, if nothing else I learned alot. I finally figured it out. When I split the plastic air filter canister for cleaning, apparently the spring on the plastic shaft that holds the choke shutter open became dislodged so the vacuum from the carb was pulling it closed, thus the reason it seemed like it was running very rich. It only took my dumb ass 5 hours of pissed off labor and nearly tearing the saw apart to figure this out. Once I placed it back in the groove and fired it up, Viola! Running like new again. Its always the little simple things that trip me up. Cut a couple ricks of oak last night with brand new chain and performed like a champ.

Thanks again TW members for all the helpful advice!