If your mower has the auto choke, it seems plausible. Run the mower in a clean area with the filter and cover off. Does the choke plate eventually open?

I don't think it would run that long with a stuck choke. It's easy enough to check the spark when hot, if you pull it, attach the cable and have someone run the starter while you hold it against the head (with gloves on). More likely it's fuel, the bowl is full, but it stops when empty. Possibly a stuck (up) float or float valve.

I would do what tomplum said If your mower has the auto choke, it seems plausible. Run the mower in a
clean area with the filter and cover off. Does the choke plate
eventually open?

And Hondas will run a long time in choke mode.

I think I found the problem - and solution! I'm buying a new carb for $25, with gaskets. A Honda shop said Honda considers this 'ethanol contamination - and WILL NOT cover the repair. For $75, he will pull the carb and clean out the jets. This guy was the only mechanic I talked to who would talk about the problem. He said it is common on Honda's. Oh, and on 6-29 - every shop was backed up 2-3 weeks! They can't hire more mechanics in the summer? I'm sure hundreds of crabby old guys like me would love a summer job!
It did seem like a fuel starvation issue, as the plug was always dry when I pulled it. (even tho the mower ran fine, up to the day it didn't, which sounds more like electrical or coil). Do plugged jets act quickly like this??
So I'll take the gamble - Amazon is shipping a new carb, and I will follow up.
I have read in the past that Honda likes to blame problems on 'bad gas', and won't cover the repairs. So in 20 years, when this dies - I won't be buying another Honda! (to mow my grave site...)
Thanks for the advice. I borrowed a mower, and will get the carb on Monday.
(I want to post this carb on every site I can find - to spite Honda and the overbooked shops!)

That's probably the problem. You can prevent it by adding Sta-Bil '360' 'Marine' 'Ethanol Fuels' (blue, 8 oz dispenser bottle in the Marine section at Wal Mart) to the gas can each and every time you get gas. 1/2 ounce for 2 gallons is plenty. Any internal combustion engine using gasoline is subject to damage from ethanol fuels so don't blame Honda. I use it in every engine I have, including vehicles, and never have fuel system problems. My mower with Honda engine has been in service since 2007 and I've never even loosened the float bolt. I don't do anything to the fuel system after the last mowing of the season - just park them and walk away. Come springtime they start on the first pull.

It's not Honda's fault. Ethanol can damage small engines, We use Ethanol free gas for all our engines, lawn mover, lawn tractor, motorcycles, scooters and cars. Most of bikers and boaters know about this problem. You can find Ethanol free gas stations near you through pure-gas.org

Thanks for the tip. I only blame Honda if they don't have a warning, in BIG letters, in the manual. Which I didn't notice, when I briefly read it when new. It sounds like a common problem, and by the forums I've read, no one mentions ethanol, or carb problems.
The mechanic also suggested getting gas in 1G containers, for the mower. '5gal gets too old.' I will add sta-bil to my Walmart list.

Absolutely not honda,s fault . All small engines owners must ensure to use fresh fuel or treated ethanal fuel when stored for more than a month. perhaps the fuel manufacturers and carb manufacturers should get on the same page. Also try Startron over Stabil much better product , also available at Walmart .

Did the carb come in?

I haven't matched the numbers with the motor number yet. So I haven't ordered. I will keep you posted.

You did turn the fuel valve the correct way?

On my 28 year old Honda, it's kind of opposite of what one would expect.

It'll run a similar amount of time with just a carb bowl full of gas, if the grass isn't too high.

I thought of that. I always leave it open, except for the last run of the season. If it was closed, the mower wouldn't restart in 5min.

Its the auto choke pin ...they

I have same problem stops after a few minutes . Ive used no ethanol gas from day one .

A few things at the top of the list. Be aware that if you have a vented fuel system, they vent through the threads of the cap. A worn tank, cap thread on occasion will rear its ugly head. More times than not it is either a fuel supply problem to the carb IE yours might have a small tubular filter in the outlet of the fuel tank, it slips in the hose. Check for good flow.

The other thing fairly common on these is a blockage in the carb in the passage that travels from the outside of the stem to the top idle circuit. On two styles, it is easy to clean. One style has a plastic pilot jet at the top that will lift out once the base idle screw is removed. That small hole in the jet and the passages in the carb must be open. The other easy to clean style has a phillips screw at the top of the carb that screws into the body. Remove that screw and clean the passages. Of course, it is helpful if the main is clean, float valve is in good shape etc.