Lawn Boy w/ B&S 6.75 ft-lb Hard Starting when warm

[Nyquist]

I have an 18-month-old Lawn Boy with the four-stroke 6.75 ft-lb Briggs & Stratton engine. I would consider it well-maintained, but I suppose that is in the eye of the beholder.

This summer it started to have issues when starting after being turned off. It can be five minutes or an hour of run time. If I shut it off and try to start it back up before the engine cools down some, it will not fire. When it does finally go, a big puff of black smoke comes out, and it stumbles for 30 seconds to a minute. Then it runs great again.

It always starts on the first pull when it is cold.

I replaced the spark plug, and that took care of the issue for a run or two, but it started doing it again right away. I pulled the new plug out, and it appeared to be a little too covered in carbon for a new plug in a new engine.

I've also sprayed carb cleaner on the plug when it comes off to get rid of dirt. Even after that it won't fire. I’ve put in the old, year-old plug & it fired again when it was cold.

I plan on taking it to the dealer, but I thought I would check with the masses here since the guy I spoke to on the phone sounds less than pleasant. He also said that if it is even remotely possible that it's an issue with fuel, I'm getting charged for the labor.

I’m troubled by the fact that when I pull the plug out it isn’t very wet… just a little fuel on two sides of the base with none that I can see on the electrode.

If there is a chance that this may be fuel related I’ll try to resolve the issue myself. Should I go ahead and run a tank of gas with fuel injector cleaner in it through to rule out a gunked up carb?

Thanks.

 

[eljefino]

I'd skip the FI cleaner. It does sound like fuel. I would dump the tank by flipping it upside down and start anew with fresh-from-the-pump gas and a tablespoon or two of MMO.

If you feel slightly ambitious, the carb comes off the gas tank with a couple phillips head screws and there's a little thimble full of fuel on top of the tank. Junk collects here; paper towel it out.

 

[Letter_K]

Using any fuel additives? I did the same thing when I added Marvel Mystery Oil to my mower. I probably should have measured it out since with the smaller capacity it is easy to overdose.

Had similar symptoms. Hard starting and impossible starting once the mower was warmed up.

 

[TFB1]

Black smoke indicates a overly rich condition, could be as simple as a partially clogged air filter...

 

[Nyquist]

I did some digging and apparently the choke on these is controlled by a mechanical temperature feedback mechanism that's connected directly to the muffler. Seems like this could be an issue...

I also found some of the CARB papers for the EPA stuff. Apparently these are incredibly sensitive to a slight loss of airflow.

I'll check for dirt sitting in the carb, add some Seafoam to the gas, and replace the air filter. If it still does it, I'll take it to the dealer since the chance of it being gas is much lower.

 

[mjoekingz28]

Any update?

I have the same mower as you.