Lawnmower running rough

[modelageek]

someone just gave me a craftsman lawn mower. it has a B and S 550 series engine(maybe that is the name of the lawnmower not sure.) it runs rough, idles up and down like it might die but doesn't. I changed the oil and added fresh gas. I am going to get a new spark plug now( i dont think that is the problem).....I pulled the air filter off and it was clean and the carb looked clean....... the plug was black that i took out......could I have a bent shaft or broken piston ring or something..........thanks........and it starts right up every time

 

[modelageek]

I got a new plug. I ran it for a few minutes and the plug was covered with soot.....still runs rough.ideas?

 

[Psychopete]

Check that the choke is opening all the way, and see if the problem persists with the air cleaner removed. Dirt could be messing with the needle and seat, not keeping the correct fuel level. Float could be the problem, too. There may be a diagram that may need replaced (carb), but I am not fluent with that exact engine.

 

[modelageek]

Check that the choke is opening all the way, and see if the problem persists with the air cleaner removed. Dirt could be messing with the needle and seat, not keeping the correct fuel level. Float could be the problem, too. There may be a diagram that may need replaced (carb), but I am not fluent with that exact engine.

I dont know anything about these engines. I pulled the air filter off and started it up and sprayed carb cleaner in the carb. I fiddled with the lever that floats around. it goes into the carb and has a spring on it. the thing still runs the same. should I pull the carb off and see if something looks weird.

 

[doorgunner]

Sounds like the 4 barrel is kicking in too soon


flush the gas tank & line out that goes to the carb /then put an inline fuel filter between the tank & the carb!

Sounds like the float is acting weird OR the idle-air screw needs adjusting to smooth out the idle/or both need adjusting

does it have a good spark?

 

[modelageek]

flush the gas tank & line out that goes to the carb /then put an inline fuel filter between the tank & the carb!

Sounds like the float is acting weird OR the idle-air screw needs adjusting to smooth out the idle/or both need adjusting

does it have a good spark?

I think the gas is fine...I think it is getting to much gas. I can not find an idle screw? I think it has a good spark,

 

[UpStandingMember]

I was wondering if someone before you had mixed oil with the gas, like you would a two stroke.

 

[GoodOld85BlueBalls]

I have a craftsman older lawn mower.

Look at the bottom of the bowl on the carborator. You should see a brass nut on the bottom side that a 1/2' wrench will fit on. Remove it and turn it out slowly with the lawn mower up on its side so the gas wont come running out. Take off the bowl and inspect the rubber gasket that goes around the lip of it. I just turned mine upside down as it was leaking air arond it insted of pulling in the required fuel. While you have the brass bolt out of the bowl that you just took out of it, look at the sides of it and you will have a little flat gasket (don't loose or crack this gasket or you are SOL!) and above it you'll see two holes that come into the sides of it, one of them may be a little plugged up with crap, blow it out, this little brass bolt is hollow and acts like a jet to the carb which pulls the gas up to the carb through a venturi tube, which also can be plugged. Be very carefull of these parts if you pull the carb off to do this work as you must get every thing back in the correct holes or it will run even worse, be very careful of the float and its seat plug, put it back exactly how you took it apart. Take some pictures with your phone or a camera to refer back to.

I just fixed mine last week thats how I know this. Good luck!

 

[modelageek]

I was wondering if someone before you had mixed oil with the gas, like you would a two stroke.

I put fresh gas in it and ran it for a little bit......I just pulled the tank off and the carberator...... I did not see anything "odd" but I don't really know what i am looking at....the choke was moving fine. I am not sure what the float is. there is a small indent in the gastank/ carb gasket that had gas in it and then a rod piece of the carb sat in there. I wonder if that was the float.....it was covered wit some metal "tape"...

 

[GoodOld85BlueBalls]

Also make sure the springs and the trottle controll rods go back in the exact holes they came out of also. It may be easyest to just take the carb all the way off and work on it on your bench. If you don't put the rods back in the right places the thing will run like a banshee till parts come flying out of it, but you'll sure cut some grass while she lasts. You know what a redline is right! LOL!

 

[GoodOld85BlueBalls]

Here's a video link to a simular carb and mower to mine.

http://www.ehow.com/video_7493434_clean-carburetor-lawn-mower.html

 

[dankhimself]

Is it idling up and down like WOOOOOOObruhwoooOOWOOOOOObruhwooooooOOWOOOOO (pardon my engine noise description, its how it sounds in my head!)

90 percent of the time that is because the jet is clogged. where you pull that previously mentioned brass hollow bolt, the hole that it is threaded into contains a jet all the way up inside, blast it with and airgun after hitting it with some carb cleaner, DO NOT get any carb cleaner on any rubber parts of the carb, also that bolt you pull should have two tiny holes by the head on each side of the hollow shaft, between the threads and the bolt head, make sure they are clear, you can carb clean, air blast those as well.

The chokes may stick sometimes, but rarely. the governor may need adjustment as well, as its running look at the arm in the crank case that has a rod going to the butterfly (or throttle valve) on the carb, There is an adjustment procedure for that that escapes me right now, but ill look into it for you.

I worked at a landscape equipment repair shop for a few years before I went to bike school, I've seen everything from dity jets to soccer balls stuck in the mower blade, and customers furious at ME because their engine wont run. Just had to add that part because the customers' face was PRICELESS when I ripped the soccer ball out of his mower when he yelled at me for 5 minutes about how I seized his engine.

Good luck dude.

 

[modelageek]

Is it idling up and down like WOOOOOOObruhwoooOOWOOOOOObruhwooooooOOWOOOOO (pardon my engine noise description, its how it sounds in my head!)

90 percent of the time that is because the jet is clogged. where you pull that previously mentioned brass hollow bolt, the hole that it is threaded into contains a jet all the way up inside, blast it with and airgun after hitting it with some carb cleaner, DO NOT get any carb cleaner on any rubber parts of the carb, also that bolt you pull should have two tiny holes by the head on each side of the hollow shaft, between the threads and the bolt head, make sure they are clear, you can carb clean, air blast those as well.

The chokes may stick sometimes, but rarely. the governor may need adjustment as well, as its running look at the arm in the crank case that has a rod going to the butterfly (or throttle valve) on the carb, There is an adjustment procedure for that that escapes me right now, but ill look into it for you.

I worked at a landscape equipment repair shop for a few years before I went to bike school, I've seen everything from dity jets to soccer balls stuck in the mower blade, and customers furious at ME because their engine wont run. Just had to add that part because the customers' face was PRICELESS when I ripped the soccer ball out of his mower when he yelled at me for 5 minutes about how I seized his engine.
Good luck dude.

here is a picture the carb is sitting next to the gas tank.......I have since put it back together(took 7 minutes) and it started right up......it might have been running a little better but I am not sure....I think I have a different setup then what you guys are talking about.....on the fuel tank there are 6 screw holes. actually there are only 5 screws. the middle bottom one lines up exactly at the middle of the carb bowl........it has threads in it as if something should go there but as far as i can tell nothing was there....I don't know where this jet needle thing is
*I just looked though a Haynes small engine manual I had.......I think I have a non float vacu-jet carb

 

[modelageek]

I found a website that said B & S vacu jet carbs will run rich if the pickup tube check ball is stuck......I don't even know where that is? http://www.scribd.com/westland2009/d/22808493-How-to-Repair-Briggs-Stratton-Engines

 

[martin]

Need to know what kind of carb it has. Earlier b&s had the carb mounted on the tank,)these had a habit of diaphrams going bad. Then they went to a normal carb with a float and bowl, there's a tiny hole inthe brass tube that tends to get plugged. The newer ones have plastic carbs, i've not figured them out yet. They all have an auto throttle rod that needs to be correctly adjusted.