Have you tried using fresh recommended (87 octane) gas with no additives? A new lawnmower should not need a cleaning additive, and I would not use Stabil in gas I was going to use in a month or two.

I went to the doctor and said that when I twisted my left arm around behind my back to scratch an itch on my right side, it hurt. The doctor said 'Don't do that - that'll be $25.'
The idle setting on Honda engines with a hand throttle is problematic - quite a few of them will cut off on idle. All you have to do is to find the little screw where you can speed up the idle and you'll be fine. The main thing is, the idle setting has no useful function of any kind and should be simply ignored. You should be using the mower with full throttle at all times. If you wish to throttle back before releasing the bail to cut it off, as the instructions usually say, go ahead. I have a GSV190 engine on one mower that also idles slow and will cut off, but since idle is a non-function, I wouldn't spend five minutes or five cents trying to 'fix' it.
Keep using the good gas and Sta-Bil. You can also throw in 1 oz/1 gal Marvel Mystery Oil to keep it humming.

Xlindax, the dealer told me to use the premium unleaded. He also scared me with tales of gas going bad almost before it comes out of the tanker.

Saxman, Well, I paid extra for the BBC system so I wouldn't have to restart it every time I stopped to scratch my er, uh, head. It just seems like a waste of gas to leave it at full throttle when I'm not mowing. I will adjust the idle screw. It's not going to be the end of the world if I can't idle it anymore.

Thanks to both of you for taking time to help.

Most mowers today don't have a hand throttle, so they just continue to run at the governed speed when the blade brake clutch is engaged. The engine enjoys better lubrication and cooling at the higher speed, especially when not doing any work.
Gas today, particularly gasohol, does degrade quickly, but with the stabilizer added to the fuel can, it should be good for a year. I use mid-range myself in the outdoor power equipment because of octane drop from vapor loss when opening a hot can. I can't say that I can show a problem with the regular gas from this, but I don't want to take a chance on destructive 'pinging' in my engines either. Plus, it only comes to about a dollar a year difference. Premium fuel probably will result in more carbon formation in the mower engine but the cleaners in Sta-Bil should counteract that. About the only other tangible effect of Premium would be a measurable drop in combustion temperatures which is actually the cause of the carbon formation in lower-compression engines that do not require it for anti-knock.
Have you considered just pulling the throttle back enough to cut engine speed without bottoming it out?

I purchased my mower with the Honda 160 GVC in 2000. I have installed an hour meter on it, and it has about 580 hours on it. It has never had any kind of additive in the oil or the gas. Always had one oil change per year, at about 55 to 60 hours. Never, ever, was down more than a sixteenth of an inch on the dipstick with 60 hours on the oil change. Never used any gas other than 87 octane. I have always used Mobil one oil - 5W30 as long as it was SL, and M1 10W30 High Mileage since my supply of M1 5W30 SL ran out.

Engine still starts on the first or second pull, and runs like a champ, with 10, almost 11 years on it, and 580 hours, without any additives such as MMO, Seafoam, or Sta-Bil.

" purchased my mower with the Honda 160 GVC in 2000. I have installed an hour meter on it, and it has about 580 hours on it. It has never had any kind of additive in the oil or the gas. Always had one oil change per year, at about 55 to 60 hours. Never, ever, was down more than a sixteenth of an inch on the dipstick with 60 hours on the oil change. Never used any gas other than 87 octane. I have always used Mobil one oil - 5W30 as long as it was SL, and M1 10W30 High Mileage since my supply of M1 5W30 SL ran out. "

Yes, I agree completely. Those miracle engine cures in a bottle are good for supplementing the checking account of the person selling them. I store gas over winter in a well sealed gasoline can and have yet to encounter the problems that those gasoline extenders are supposed to cure. And I've been owing lawns for 45 years. There is no substitute for good maitenance and a bit of common sense.

This is an interesting discussion. I didn't mention that before purchasing the new Honda, I had a 12 year old Honda that never had a problem with the engine. I only replaced it because the transmission went bad and, since Honda makes you buy a whole transmission instead of replacing the cheap plastic part that broke, I decided to cut my losses.

The old Honda engine was bullet proof. It started first pull for the new owner when I was showing it. I never used stabil or Seafoam prior to buying the new mower. I was pretty good about maintenance, oil, air filter, plug, etc.

The gas that supposedly caused my new mower's carb to go bad was used in a Briggs four cycle edger and in a two-cycle blower and weedeater without problems.

I'm starting to come to the conclusion that my original carb problem was not due to bad gas, but to a problem that is inherent with the carb, as Saxman said. I'm just going to sit back and see what happens with the replacement carb. If it gets to the point where it is just as bad as the original carb, I might go back to the dealer and try to get the first carb covered under warranty.

I'm still wondering about the additives. I seem to have some pretty good experts on both sides of the argument. I guess since I'm working with a dealer that told me to use additives, I had better keep doing it at least until I get the carb situation resolved.

Boy, am I glad I didn't buy it at a big box store. It wouldn't be fun having to deal with them in this situation. Thanks again to all!

What does the engine manual say to put in the fuel? A lawnmower dealer might be just the same as many new car dealers, in that they might be recommending additives to increase their own bottom line. Like the previous poster, I have used fairly old, 3 or 4 month old, gas with no problem.