Keeps running but won't start when pulling the cord.

Wow, thank you very much. One final detail to be sure it doesn't change anything, I can let the mower run for, let's say 30 minutes, then turn it off. It's good and warm now, and, I have the same problem. It doesn't matter how long the engine runs. And when I engage the blade, it does it well.
 
Your engine is 128T02-3256-B1.

It looks like you have a primer bulb on this engine. I'm sure you are, but if you aren't pressing that, your problem is there.
I personally do not think it is a needle and seat issue, because you said that it runs fine until shut off. In my experience, an engine with a swollen needle and seat will run for just a short time before dying. Because it is running fine once on, I suspect a primer issue.

If you have a primer bulb do this:

Take off the air cleaner (one 8mm bolt at the top of the airbox, or use flathead)

Press the primer bulb a lot of times while looking down the throat of the carburetor. If you see gas start to accumulate in the carburetor the primer is working correctly. If you do not, the primer isn't working correctly. Of course if this is working and gas pools in the carburetor wipe away any excess gas for safety reasons.

I bet you'll find this isn't working.
 
BlufftonJim said:
In the ten years I've had this mower, I never noticed a primer bulb. I will look for it.
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Nevermind I'm sure there isn't one if you haven't found one then. It would be noticable. Bright red, on the left of the front of the engine on the air cleaner. Maybe your auto choke isn't working then. Or maybe it is the needle and seat after all. I could be totally wrong. I just think it wouldn't be that because it stays running.
 
Pull your air filter and look at the choke plate. It should be totally closed when engine cold. If not...1. Air Vane is out of adjustment. 2. Air vane spring is bad.3. Tstat is bad. 4. Lots of crud in there keeping air vane from moving freely.
 
dougand3 said:
Pull your air filter and look at the choke plate. It should be totally closed when engine cold. If not...1. Air Vane is out of adjustment. 2. Air vane spring is bad.3. Tstat is bad. 4. Lots of crud in there keeping air vane from moving freely.
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That's what I was thinking, since there is no primer bulb and it runs good once started.
 
Yes, it could be any of those, but I do over 100 of those engines a year and the most common problem is the float seat. If it hasn’t been looked at in 10 years I’m sticking to the seat.
 
Rivets said:
Yes, it could be any of those, but I do over 100 of those engines a year and the most common problem is the float seat. If it hasn’t been looked at in 10 years I’m sticking to the seat.
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Fair enough. Took one apart today just for maintenance and hard starting and the seat was slightly swollen. Fixed that. No harm in checking the needle and seat.

Disassemble it according to this video
If you don't have the locking pliers they use on the fuel line then just drain what you can first and be ready to clean up a little spill
If you don't have SAE hex sockets equivalent metrics will work: 6mm for 1/4 in, 8mm for the filter housing and 10mm for the carburetor mounting to the engine. You can use a ratchet instead of a screw driver.
When you get it to the point that the float bowl is off but the float is still in, hold it up side down and observe the float. Make sure it is 'level' to the rest of the carburetor body, NOT like this: (or the other way around sticking up) taryl.png

If it's not level like that then there's your problem. Bad news: It's really expensive to fix. $1.00 Needle and seat. (Kidding its cheap and easy).
An air vane is a piece of plastic under the blower housing that is pushed by the 'wind' generated by the spinning engine and when pushed it adjusts the carburetor to get the right RPMs.
 
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