HELP! Ms 290 stihl

[Frognc97]

I’ll start by ms ms290 is holding 10lbs of pressure and vacuum. I have no idea why it’s wanting to revv up on its own. To me the tank has awful lot of pressure. Faulty tank vent? I always start with pressure test to identify my leak but I’m stuck on this. Thanks in advance

 

[jmester]

Here is the pages from the service manual on how to test the tank vent.
Operation of tank vent at gauge
pressure: 0.3 bar (4.35 psi)

 

[jmester]

 

[jmester]

Not sure why the screen shots are blurry. Hopefully they will be ok

 

[Wood Doctor]

Tank vent may be OK. Could be the linkage from the throttle is providing a goose to the carburetor. Check the trigger connection also. Carb replacement might be needed. The 290 has been around quite a while.

 

[EFSM]

Make sure the intake boot and pulse line are fine (maybe that is tested in your vacuum test). Check for carb issues and cracked OR KINKED fuel lines (aftermarket lines tend to kink next to the carburetor fitting).

 

[lehman live edge slab]

If the fuel lines and filter haven’t been replaced or were aftermarket parts they could be an issue for sure. Original line could be soft and collapsing/kinked. I’d just give the fuel system a complete overhaul, rebuild and clean carb, new fuel line and filter all oem and odds are it will straighten itself out.