Stihl 021 won’t throttle up, help?

[Chainsaw Collectors]

I got a Stihl 021 chainsaw. I gave it a decent drink down the carb and it idled perfect for 1.5 minutes, gas tank full also, tried revving a tiny bit a couple times but dies or tries to die immediately. It does have a muffler mod and timing advancement. What does the line with a spring in it do? It goes a very tiny ways into the tank like a return line. Is that line broken? What are the proper carb adjustments for this saw? Currently has a Stihl carb, but I do have a new Chinese carb for it if needed. Fuel line and filter look good to me but maybe I’ll replace them anyways. I may possibly be interested in a stihl logo for the recoil and a rear throttle handle assembly in the future for this saw if anyone has one, or a parts saw. Any help would be greatly appreciated, thanks for your time.

 

[2StrokeFondler]

It's not a spring, it's a screw. That's the tank vent.
One turn out for H and L should be the default. But you still need to proper tune it.
Instead of changing the carb, I'd change the diaphragms from the Chinese carb to the OEM one if it won't run on the default settings.

 

[SteveSr]

I got a Stihl 021 chainsaw. I gave it a decent drink down the carb and it idled perfect for 1.5 minutes, gas tank full also, tried revving a tiny bit a couple times but dies or tries to die immediately. It does have a muffler mod and timing advancement. What does the line with a spring in it do? It goes a very tiny ways into the tank like a return line. Is that line broken? What are the proper carb adjustments for this saw? Currently has a Stihl carb, but I do have a new Chinese carb for it if needed. Fuel line and filter look good to me but maybe I’ll replace them anyways. I may possibly be interested in a stihl logo for the recoil and a rear throttle handle assembly in the future for this saw if anyone has one, or a parts saw. Any help would be greatly appreciated, thanks for your time.

If it will idle all day but won't rev up it could be that the main nozzle check valve is stuck closed. This is a common issue with old Zama carbs. I had an 021 that was intermittent like this. Would run fine one day and not the next. This is most likely non-repairable. Your China carb may have other issues.

 

[stihltech]

Accelerator pump.
I just caught what spell check did.

Accusatory pump? In some ways.

 

[singinwoodwackr]

They are $100 saws so don't put too much $ into it.
Rebuild the carb.