ms 260 pro fluctuating idle

[columbo]

hi all I am a newbie I bought a used ms 260 very clean looks like all original the piston and cylinder are perfect . had the original carb wt 403 no L adj. the saw would not idle consistently but at wot runs great . when I put the saw on the ground it the idle will get low and sometimes stall . pick it up and idle raises up . seems like a strange problem. so I replaced fuel line , impulse line fuel filter and intake boot . they looked fine but I figured I would replace just in case . still no change . I also replaced air filter . and a cheap china carb . still same problem . then I checked crank pressure and vacuum test it was perfect I really thought I had a crank seal leak but not so . I also cleaned exhaust screen which was slightly clogged and drilled 2 3/16 holes in muffler . still no change . I lastly picked up a walbro wt 194 and installed it . it helped a little but still cant get consistant idle . thanks for any advice that you can give . the saw cuts great but is a pain at idle . plus its super clean . thanks

 

[SteveSr]

hi all I am a newbie I bought a used ms 260 very clean looks like all original the piston and cylinder are perfect . had the original carb wt 403 no L adj. the saw would not idle consistently but at wot runs great . when I put the saw on the ground it the idle will get low and sometimes stall . pick it up and idle raises up . seems like a strange problem. so I replaced fuel line , impulse line fuel filter and intake boot . they looked fine but I figured I would replace just in case . still no change . I also replaced air filter . and a cheap china carb . still same problem . then I checked crank pressure and vacuum test it was perfect I really thought I had a crank seal leak but not so . I also cleaned exhaust screen which was slightly clogged and drilled 2 3/16 holes in muffler . still no change . I lastly picked up a walbro wt 194 and installed it . it helped a little but still cant get consistant idle . thanks for any advice that you can give . the saw cuts great but is a pain at idle . plus its super clean . thanks

Idle stability can be affected by leaking crank seals. This needs to be tested and ruled out. There are plenty of threads on crankcase pressure and vacuum testing.

This saw, especially combined with the WT-403 carb, can experience fuel pooling in the intake. If the idle changes or the saw stalls when the bar is pointed down you have fuel pooling. You can greatly improve this behavior by keeping the "L" screw as lean as necessary to prevent this. The WT-426 carb also seems to work better on this saw in this regard.

 

[Vintage Engine Repairs]

Fuel pooling in the manifold is your issue. As above run the L as lean as you can whilst it still being properly tuned. There is a lip / step on the intake of the cylinder which fuel pools at. Put your saw down or pick it up and it gets released which drops the RPM’s and can cause it to stall. It’s a model specific flaw. You can smooth this step down to create a slope with a Dremel if you wish.

 

[drf255]

Fuel pooling in the manifold is your issue. As above run the L as lean as you can whilst it still being properly tuned. There is a lip / step on the intake of the cylinder which fuel pools at. Put your saw down or pick it up and it gets released which drops the RPM’s and can cause it to stall. It’s a model specific flaw. You can smooth this step down to create a slope with a Dremel if you wish.

Bingo

Go over to Outdoor Power Equipment forum and look up “026 carb” thread. It’s recent and shows the issue.

 

[Vintage Engine Repairs]

Bingo

Nice to be able to share great advice I was given

 

[grizz55chev]

Bingo

Go over to Outdoor Power Equipment forum and look up “026 carb” thread. It’s recent and shows the issue.

You said the OPE word out loud, and didn't get bleeped!

 

[columbo]

Idle stability can be affected by leaking crank seals. This needs to be tested and ruled out. There are plenty of threads on crankcase pressure and vacuum testing.

This saw, especially combined with the WT-403 carb, can experience fuel pooling in the intake. If the idle changes or the saw stalls when the bar is pointed down you have fuel pooling. You can greatly improve this behavior by keeping the "L" screw as lean as necessary to prevent this. The WT-426 carb also seems to work better on this saw in this regard.

thanks i have checked the crankcase pressure and vacuum they both held for at least 15 minutes

 

[columbo]

Fuel pooling in the manifold is your issue. As above run the L as lean as you can whilst it still being properly tuned. There is a lip / step on the intake of the cylinder which fuel pools at. Put your saw down or pick it up and it gets released which drops the RPM’s and can cause it to stall. It’s a model specific flaw. You can smooth this step down to create a slope with a Dremel if you wish.

thanks for that info i tried everything else like i said the saw cuts great at wot but a real pain when you are cutting firewood . i will keep it lean and maybe one day try the dremel trick .