Why does my B&S model 092908-5212 start, but run for less than 5 seconds?

Does not run, will start with starting fluid – Mantis 2-Cycle Tiller

Will only start and run in choked position, when throttle applied chokes out. If started with out choke and throttle position in low speed will start and run for 10 sec then like it runs out of gas.

Lawn mower will start and run for 5 seconds and shut down

Chainsaw stalls Chainsaw is 4 years old and has a history of moderate use. After I ran the saw about 1 minute on plain gas (grabbed the wrong gas can – ouch) the chainsaw sputtered and stopped.

It didn't seize, and the pull starter never became more or less difficult than normal. The engine would continue to start if I pressed the prime bulb and engaging the choke, but stall again after 10-20 seconds. The temperature that day was about 50 degrees F and I was running the saw with the “cold plug” installed (per warm weather running).

When it refused to keep running I did the following:
Flushed the fuel tank (that's when I saw the gas had no oil in it).
Ran hardware wire through all of the fuel lines.
Replaced the fuel filter and spark plug.
Cleaned the air filter with a nylon brush and compressed air.

Same behavior (start then stall in less than 20 seconds). I made at least 20+ attempts to start it.

I removed the carburetor and, though it looked perfectly clean, I took off the top and bottom covers then sprayed everything with automotive carb cleaner and blew out the passages with compressed air. The gasket and diaphragm looked new. No pinholes in the diaphragm when held against a bright light. I reinstalled the carb but got the same behavior (start then stall in less than 20 seconds). I again made at least 20+ attempts to start it.

I disassembled the short block and saw that the piston has some slight scoring on it. The ring is clean and I verified that the piston ring has .001 clearance between it and the piston ring groove all the way around with the ring held tightly in place (I was thinking that the piston might have become deformed if it did indeed get too hot when run without any oil premix).

The cylinder wall has no scoring and there isn't any signs of melted aluminum anywhere. The crank is clean as was the inside of the crank cover.

I reinstalled the crank cover using permatex non-hardening gasket goop and torqued the cover bolts to 10 inch pounds. I reassembled everything else per the exploded diagrams in Echo's “parts manual” for the CS400.

During assembly I took note that both the carb gasket and intake boot look like new.

Still the same result: press prime bulb once, engage choke, pull a few times and it starts but stalls after 10-20 seconds.

I'm stumped.

Weed eater starts but won't stay running – Weedeater 19 in 25cc Gas Hedge Trimmer

Can get it to start, but runs about three seconds and stops. the choke is pushed in. But seems to want to run longer with the choke out. 4 seconds…

It’s brand new, when I finally get it started it will run good for about 1 min. or less, and then it dies. I pull the choke out all the way, pull it a couple of times, push it half way in, it starts but it’s like it doesn’t have the power to turn the chain, bogging out and then it dies, I will never buy another homelite product, or recommend anyone else to, this is my second one, the first one leaked gas, Home Depot really should quit selling them, there making you look bad too!!

Seems to start easily run for a few minutes and then slow and stop–bulb remains full –gas is good–have tried half choke in case too lean–did not solve–also seems possibly related to the angle I hold it at–seems to cut out quicker if blower tube angled more downward.