Another B&S 550EX in a Troy-Bilt TB110 push mower

austinrick

Forum Newbie
Joined
Aug 24, 2025
Threads
1
Messages
2
Greetings! New member here.

A neighbor was gifted the above referenced mower; told me it started and ran fine for at least one lawn mowing (and many years with previous owner), then she filled with some bad/old gas and it hasn't worked since. I offered to go into it for her, believing with all my heart that it was a matter of taking down the carburetor and clearing out the ethanol gook, like I did on my Craftsman B&S. Naturally, it has become lots more complicated than that.

I can't find anything like a motor model/serial number stamped at any of the three places B&S says to look. But on the right (starboard) side of the block, on a largish flat, black painted surface, printed in a silver ink, is 9P702-0144-F1 and DOM 03 24 15 – nothing more. The manufacture date does not resemble a B&S "date code" as they describe it. I was able to use the first number to locate and download a parts manual from the B&S website. I find conflicting data regarding which carburetor is on this motor. There is a break by date and it's as if the original carb is used after the given date and replacement number used earlier. Makes no sense, so I don't know which carb to order if I choose to replace this one.

Anyway, the issue is the same as many others have had with this motor: Starts, runs rich while it warms up, then dies. I have had the carb apart several times; all seems well there. I don't think the carburetor is the root of this problem. New spark plug didn't fix anything, naturally. Auto-choke is functioning as it should. Levers moving freely, nothing binding.

I'm wondering if the governor lever is a factor in this. It's a part of these small motors that I don't understand. The mechanism seems to be moving freely; all springs are in good shape. When running and warming up, I found I can reach under the top cowling, put a finger on the governor lever, push it forward a hair and the engine immediately picks up and runs like it should. But not for long. I kept working that gov lever to keep the engine going, but it finally conked out. After that I can pull the start cord a few times slowly, then one time hard; the engine fires and dies.

Is the problem in the governor? This mower ran fine for years. Everything on and around the carburetor seems fine. What am I missing? -TIA
 
Last edited:

ILENGINE

Lawn Royalty
Joined
May 6, 2010
Threads
51
Messages
11,303
From the symptoms the problem is still in the carb, or you have a flow issue coming out of the tank/fuel line, or something stuck in the fuel inlet on the carb causing issues. The engine uses the 799584 carb since your build date is before 07/01/18
 

Auto Doc's

Lawn Addict
Top Poster Of Month
Joined
Sep 7, 2024
Threads
15
Messages
1,207
Greetings! New member here.

A neighbor was gifted the above referenced mower; told me it started and ran fine for at least one lawn mowing (and many years with previous owner), then she filled with some bad/old gas and it hasn't worked since. I offered to go into it for her, believing with all my heart that it was a matter of taking down the carburetor and clearing out the ethanol gook, like I did on my Craftsman B&S. Naturally, it has become lots more complicated than that.

I can't find anything like a motor model/serial number stamped at any of the three places B&S says to look. But on the right (starboard) side of the block, on a largish flat, black painted surface, printed in a silver ink, is 9P702-0144-F1 and DOM 03 24 15 – nothing more. The manufacture date does not resemble a B&S "date code" as they describe it. I was able to use the first number to locate and download a parts manual from the B&S website. I find conflicting data regarding which carburetor is on this motor. There is a break by date and it's as if the original carb is used after the given date and replacement number used earlier. Makes no sense, so I don't know which carb to order if I choose to replace this one.

Anyway, the issue is the same as many others have had with this motor: Starts, runs rich while it warms up, then dies. I have had the carb apart several times; all seems well there. I don't think the carburetor is the root of this problem. New spark plug didn't fix anything, naturally. Auto-choke is functioning as it should. Levers moving freely, nothing binding.

I'm wondering if the governor lever is a factor in this. It's a part of these small motors that I don't understand. The mechanism seems to be moving freely; all springs are in good shape. When running and warming up, I found I can reach under the top cowling, put a finger on the governor lever, push it forward a hair and the engine immediately picks up and runs like it should. But not for long. I kept working that gov lever to keep the engine going, but it finally conked out. After that I can pull the start cord a few times slowly, then one time hard; the engine fires and dies.

Is the problem in the governor? This mower ran fine for years. Everything on and around the carburetor seems fine. What am I missing? -TIA
This problem favors a bad heat thermostat on the muffler that is not opening the choke has it warms up. The other problem is if the choke linkage is getting hung up for some reason. The top cover and shroud need to be removed for closer inspection

Copy and paste your engine information i your browser, then look for parts tree. There were different muffler options, so you have to match the one you have.

03/24/15 is your date code as far as I know.
 

austinrick

Forum Newbie
Joined
Aug 24, 2025
Threads
1
Messages
2
This problem favors a bad heat thermostat on the muffler that is not opening the choke has it warms up. The other problem is if the choke linkage is getting hung up for some reason. The top cover and shroud need to be removed for closer inspection

Copy and paste your engine information i your browser, then look for parts tree. There were different muffler options, so you have to match the one you have.

03/24/15 is your date code as far as I know.
Thanks, but I have confirmed that the auto choke is working as it should: choke butterfly is completely closed when cold, fully open when hot. I can't fault the choke. Also, after reading some other comment somewhere, I checked to see if the choke lever was able to get hung up against the air cleaner mounting bracket, and it was, so I filed a little plastic off of that lever and now there is visible daylight between lever and bracket. That's part of what's so frustrating about this; everything seems perfectly fine: carb, linkages, choke. What's left? Governor?

It's not my mower and not my money, so I hesitate to spend my neighbor's money on something like a $40 carburetor when this one seems fine. I could buy a cheap main jet, but 1) reviews say they don't fit properly, and 2) I don't think there's anything wrong with this one.

But when I pushed the governor lever forward (with machine running) it did try to run properly. It just couldn't keep it up. I don't get it.
 
Top