Push mower wont stay running unless I hold air vane open for 45sec

[moebattler]

Mower model - Troy-Bilt 12AV566N011
Briggs Stratton model - 126T02-0487-B1
Auto Choke

Problem:
Mower sputters after start and eventually shuts off. Found if i manually hold the air vane arm open for 45sec to 1min...everything warms up and the mower runs fine. I have to do this for every cold start.

What i did:
Replaced gasoline
Changed oil
Replaced spark plug
Cleaned carb
Replaced spring which controls air vane
Replaced thermostat (which pushes against the air vane to open)
Did not replace air vane itself because its just a piece of plastic and seems like in fine shape.

So the mower works fine after what I mentioned but quite a pain to hold that open after every start.

Any suggestions are appreciated
Thanks

 

[Rivets]

Did you adjust the air vane when you replaced the thermostat? Sounds to me like the choke is not opening properly on startup. Should have been instructions on how to adjust with the new thermostat.

 

[moebattler]

Thanks for the response. Yes I placed it so the thermostat hits and pushes against the middle part of the vane. When i manually move the thermostat, it moves easily and pushes the vane without any resistance. Seems like its where it should be.

 

[moebattler]

Can I take the muffler off and try to watch what the thermostat does while starting?

 

[VegetiveSteam]

Just a couple of thoughts. Maybe see if you can find out what the RPMs should be on this engine and make sure they're not below what they should be. If the RPMs are low there might not be enough air movement to force the air vane to move as far as it's supposed to. I don't know if this is even possible to get out of adjustment but I'd also check that the bracket that the air vane spring attaches to didn't somehow get bent and putting excessive tension on the spring in turn not letting the air vane move as far as it should.

 

[VegetiveSteam]

Can I take the muffler off and try to watch what the thermostat does while starting?

Without the muffler I'm not sure the thermostat will work correctly so that may not tell you anything.

 

[moebattler]

Thanks Vegetive Steam ..appreciate the response - I like the idea of checking brackets where spring is attached but thinking I don't want to adjust too much because all works fine after the engine 'warms up' and do not want to cause an additional problem. And you're right ..can't have the muffler off to monitor the thermostat

​

 

[enigma-2]

After reading all of the posts, seems to always come back to the thermostat not opening or opening far enough.

 

[VegetiveSteam]

Thanks Vegetive Steam ..appreciate the response - I like the idea of checking brackets where spring is attached but thinking I don't want to adjust too much because all works fine after the engine 'warms up' and do not want to cause an additional problem. And you're right ..can't have the muffler off to monitor the thermostat

​

I agree. You don’t need to cause more problems. Just see if anything looks out of place or bent. It’s a pretty simple system so there aren’t too many things to check.

 

[bertsmobile1]

The important question
Are you holding the choke on or off
The air vane pulls against a spring when the engine is cold
So the choke is only on for a second or two
Once the engine gets to 1/2 speed the air vane should hold the choke OFF
When hot the thermostat holds the choke OFF because you do not need the choke to start a hot engine
To me it sounds like the spring is too weak to hold the choke on long enough for the engine to warm up
The thermostat must be working fine if the mower hot starts OK