Lawnmower not running even, air intake flap does not open

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python01

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I have older lawnmower that run like a charm till this past weekend.
Now when I started it it did not run even, very erratic and black smoke coming out of the muffler so I figured the gas mixture must be too rich.
After some time I figured that the flap in the air intake under the air filter is not opening up to allow more air to mix with gasoline.
When I took off the air filter and used the screw to manually open that flap the engine picked up and run nicely, when I let it go it goes bad again.

How does that flap normally open? Is there mechanical link to force it open or does the increased airflow suppose to push it open?
What can I do to fix it?

Here is a link to the video file I have done to demonstrate what is going on:
http://www.mcmasteraccommodations.ca/LawnmowerIssue_1.mp4

Any help will be greatly appreciated.
 

oldognewtrick

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Did you find a small spring or parts of a spring lying around? Looks like one for the choke is missing.
 

python01

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Would that spring be on the outside or inside? I have not seen any parts of a spring on the inside or outside. Do you have any picture so I know what I should be looking for and where it should be located?
Can these parts be bought for replacement?
 

bud16415

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That’s called the choke plate and on old mowers it had a lever you pulled to choke the engine to make the mixture richer to start the engine and as it warmed up you opened the choke slowly. Yours is what they came up with for people that didn’t know how to start an engine and it is an automatic choke. It is gummed up or is missing a spring but I don’t think there is a spring for that. They sell rebuild kits that have a few key parts that wear out. Most of the time if you take the carb apart and clean it good with carb cleaner it will start working. Or you could rig a manual choke off the shaft that it rotates on that does what you are doing with the bolt.
 
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