KM-131R idle issue

[RPower]

I have a weird one in the shop: it's a relatively new KM-131R that refuses to give me a stable idle. I replaced the carb with a cheap Chinese unit which netted me nothing, I then found out about the tank vent issue, replaced the vent and put the old carb back in and now I have a machine that runs but won't idle below like 4 grand. I can get it stable with Low and idle screw for a few seconds then it will either crash or rev up out of the blue. I'm thinking my next move is to buy a real Stihl carb but I thought it couldn't hurt to see if someone has run into this before.

Thanks in advance for any help, Chet.

 

[Brad Button]

It sounds like you may have an intake leak. Have you done a leak-down test?

 

[bogieboy]

Air leak, 100%.... i have seen the odd one have a loose intake bolt, or a crank seal slide out, or a poor dirko job on the pan or timing cover, and had one with the valve cover gasket slid out of place...

Also, verify the valves are .01mm lash, they can get very wonky once they get out of spec.

 

[TheWizard]

I would say def an air leak but I had similar with my km130. I set the valves spot on and it ran but started playing up again so back to the valves. They are a pain, should be very simple and easy to set but they go out so easy, when it's right it's good but can be frustrating. Why did stihl both under pressure from climate do gooders and bringing out new models. New is not always better.

 

[RPower]

Thank You! Thank You, to all of you! After fifty years of thinking of valve cover gaskets as a place to be concerned with what's leaking OUT, I never even considered that air might be leaking IN. %#$^&@!!!

I sure hope I can pay this forward one day soon.

 

[RPower]

I would say def an air leak but I had similar with my km130. I set the valves spot on and it ran but started playing up again so back to the valves. They are a pain, should be very simple and easy to set but they go out so easy, when it's right it's good but can be frustrating. Why did stihl both under pressure from climate do gooders and bringing out new models. New is not always better.

It was an air leak, and I do agree that the climate do-gooders don't have a clue but it's hard to beat the low end torque of a 4 stroke. I think the 4 mix probably has a solid place, especially when powering tools like brushes and the like. It's Stihl that really gets my ire up. You can't get a damn bit of information out of them. You can't get parts at anything but full retail. It's like trying to work with John Deere. Yet my shop is always full of green things and white and orange things, so there isn't much choice. Meh.

Thanks again for the help.

 

[EFSM]

I think the 4 mix probably has a solid place

It's interesting that Echo just launched their first valved engine in the states, the 5810 blower. It outperforms its predecessor, the 580, considerably. Overall, on trimmers I think Stihl's 4-mix is a little on the heavy side, which they compensate for with thinks like too-light antivibe shaft clamp, etc.