Stihl MS 260 Pro

chenangokid · March 26, 2021, 08:12:00 PM

hello i am new to forum thanks for having me i am not a mechanic but i do some repairs
i bought a used ms 260 pro very clean i am having trouble getting it to idle properly
it will fluctuate and sometimes stall but cuts well on full throttle.
ok the piston and cylinder are perfect . i checked gas line , impulse line , and intake boot all looked fine but i replaced them any way and no change . it still had orig carb wt 403 with only L adjustment and La so i replaced with cheap China carb still same prob . i also replaced fuel line . i also checked crank case pressure and vacuum they both held perfect .
i also cleaned exhaust screen which was dirty and drilled 2 extra 3/16 holes in muffler and still no change . i would appreciate any ideas thank you . it is a very clean looking saw .
thanks for any suggestions

chenangokid · March 26, 2021, 08:13:47 PM

P S i also changed air filter

chenangokid · March 26, 2021, 08:15:19 PM

one more thing my next move was gonna be buying a walbro wt 194 and try that

DHansen · March 26, 2021, 08:47:46 PM

What will the saw do if you lightly choke it while at idle? After it stalls does it restart easy, or hard? Do you have to choke it again when you try to restart it? After a stall out and before attempting a restart, pull the spark plug and see if it is wet or dry? Black or tan electrode color? Have you tried, while the saw is running, spraying carburetor spray near the clutch side crankshaft seal?

chenangokid · March 26, 2021, 08:52:11 PM

not sure what happens if i lightly choke it i will try tommorrow it restarts easy but i have to give it some throttle . the plug is slightly black no i did not try spraying car b spray on clutch side of crank seal but both pressure and vacuum test held perfect .

DHansen · March 26, 2021, 09:00:02 PM

Might be nice to try and eliminate a variable. See if you can determine if it is lean. A vacuum leak drawing in unmetered air will affect idle more than high speed operation. The % of leak vs % of consumed air rate. At idle by choking it slightly you will compensate for the leak or lean condition. With the spray you may be able to pinpoint your leak. Don't get carried away with the spray. No lubrication with the carb spray and it can be flammable. I have seen a saw catch on fire from a worn spark plug wire and brake cleaner spray. Carb spray is a little less flammable.

chenangokid · March 26, 2021, 09:35:48 PM

thanks for help i will try choking it a bit at idle but if ir had a vacuum leak wouldnt it have showed when i did crank case pressure and vacuum tests ?

DHansen · March 26, 2021, 10:21:26 PM

I would think so. How high of vacuum did you achieve and how long did it hold? I'm sure others with more knowledge will chime in with suggestions.

DHansen · March 26, 2021, 10:24:47 PM

Does this saw have fuel management. Not sure what Stihl calls their auto tune system.

mike_belben · March 26, 2021, 10:38:30 PM

No 260 pro was carbed.

Read the tuning section on madsens saw shop page and start there. See if you can get the low screw to the highest idle position then bring the LA down until the chain sits still.

chenangokid · March 26, 2021, 11:28:29 PM

the vacuum held for at least 15 minutes
and i can get the idle to stop chain from turning then all of a sudden the idle will race and the chain will turn like its sucking air all of a sudden i am thinking of trying a w t 194 carb as a last resort

chenangokid · March 26, 2021, 11:30:18 PM

and i did read carb adjustment procedure but it seems to change on its own

chenangokid · March 26, 2021, 11:33:07 PM

i was almost sure i would find one of the crank seals leaking i was actually dissappointed i didnt lol i hate to give up on it cause its such a clean saw

DHansen · March 27, 2021, 08:23:18 AM

Does the idle speed increase by itself, just before the saw dies?

As it is about to die, can you throttle the saw up and prevent it from stalling?

chenangokid · March 27, 2021, 08:45:37 AM

no it doesnt increase but if i give it gas it wont die

sidehill6 · March 27, 2021, 09:04:52 AM

are you located in chenango county? some really good saw guys here on the forum from surrounding counties.

DHansen · March 27, 2021, 04:10:10 PM

Any update, more information? Based on description it sure sounds air/fuel related. Have you tried to richen up the idle circuit?

donbj · March 27, 2021, 04:32:23 PM

Fuel lines in good condition? Change filter in tank? May not suck enough fuel at idle with a plugged filter.

chenangokid · March 27, 2021, 07:42:36 PM

no I had a camp in Chenango which I sold last year I am near Troy close to Vermont border
and yes I did adjust idle circuit a few times I also changed fuel filter in tank and fuel line and impulse line and intake boot I am goint to try a walbro 194 carb that is my last hope at full throttle it cuts great just a pain that it wont idle but not all the time sometimes it will idle I did not change the tank vent but I cracked the gas cap and it didn't help

chenangokid · March 27, 2021, 07:44:59 PM

nice pup Hansen btw

DHansen · March 27, 2021, 07:59:15 PM

Thank you. He passed away last Saturday. He would have been 16 this July. His name was Fred.

chenangokid · March 27, 2021, 08:06:55 PM

sorry to hear that is the hard part I lost a few over the last 10 years I know it hurts RiP Fred
the older I get the more it hurts

chenangokid · April 01, 2021, 11:13:10 AM

i replaced the carb with a walbro 194 I guess it helped a little . but I noticed when you put the saw on the ground the idle gets low and wants to stall then if you pick it up the idle raises up

DHansen · April 01, 2021, 11:30:42 AM

When you pick it up and the idle speed increases, does the chain start to turn? Does it make a difference if you pick it up off the ground with the brake handle vs the handle bar? How much does the rpm's change?

chenangokid · April 06, 2021, 10:02:07 AM

I recently found out it is a problem with fuel pooling in the intake . I was told there is a ridge on the cylinder intake that pools the fuel and when you pick it up the fuel drops I comb chamber causing idle to increase . I would have to grind the ridge or lip on the intake of the cylinder which might help supposedly it is common with some ms 260 s I have not look at my cylinder yet but next time I have it apart I will check . hope this helps someone else with the problem . Go over to Outdoor Power Equipment forum and look up "026 carb" thread. It's recent and shows the issue.