Stumped on a km90t

[sapponetta]

Hello,

I work for a landscaping company that specializes in high end work, natural scapes, Japanese gardens etc. All the mechanical and equipment maintenance falls on me. From gas trimmers to cats.
I have a km90t, has compression. Leakdown checks
Fuel lines are clear and delivering fuel to the carb. Has a very small pin hole in lower line that will only dribble if you press it a certain way. Probably came from me removing the lines a half dozen times.
Has stong spark.
Fresh valve adjustment (it's a 4mix)

It will start sometimes for a split second if you've been like turning it upside down, on its side etc and then immediately stall.
Will not start on starter fluid.
No issues with tank venting

I'm completely stumped.

 

[Fish]

I would replace the fuel lines, go through the carb, replace the plug, then adjust the valves.

 

[sapponetta]

I would replace the fuel lines, go through the carb, replace the plug, then adjust the valves.

Forgot to mention I went thru the carb.....more times than I care to admit. Fresh plug, strong spark. Vale lash adjusted. Leakdown good. Spent 2.5 hours on this thing before I posted this and usually I can diagnose any Stihl in a couple minutes. We have 50 pieces of equipment from them. and honestly didn't see any issues with the carb. Especially in the common places and was able to pump fluid thru the main jet.

But I was just so stumped I sprayed starter fluid directly into the intake with the carb off the engine and it had combustion every single time. So I ordered a replacement carb.

 

[Hammermechanicman]

4 mix things to check.
Valve cover not sealed.
Cam worn.
Valves out of adjustment
Bottom of crankcase not sealed.
Bad crank seals
Cam cover not sealed.
Low compression
Carbon buildup
Impulse line
Carb/fuel issue.

 

[bertsmobile1]

Double check that the fuel lines are right way round
Usually if it only runs after being upside down or when the tank is full to the filler neck it is because the fuel lines are backwards and the carb sucks air through the return line .

 

[Tiger Small Engine]

Double check that the fuel lines are right way round
Usually if it only runs after being upside down or when the tank is full to the filler neck it is because the fuel lines are backwards and the carb sucks air through the return line .

If you have a pinhole leak in fuel line, it will suck air and draw fuel correctly often. First move is to replace the damaged fuel line.

 

[sapponetta]

If you have a pinhole leak in fuel line, it will suck air and draw fuel correctly often. First move is to replace the damaged fuel line.

The pinhole was not there initially when we were having the stalling and eventually no start. It came from me removing the line about a dozen times....Either way, I ordered a new carb and fuel time kit from Stihl.

 

[sapponetta]

Double check that the fuel lines are right way round
Usually if it only runs after being upside down or when the tank is full to the filler neck it is because the fuel lines are backwards and the carb sucks air through the return line .

Fuel lines can't be swapped. They are completely different lengths, also, we have a dozen of these. I'm very familiar with them. Thanks for all your help everyone. It starts everytime on starter fluid with no carb installed. So I ordered a carb a fuel kit. Never had an engine that wouldn't start on starter fluid thru the carb before. But whatever. That's what really threw me off here.