8 HP driving snowblower has Lauson carburetor. Carb started leaking gas out the air intake port. Have changed two seat/needle set, one float and spent >10 hours trying to get the gas to quit running out the carb. Have adjusted float more times than enough and over flowing seems to stop. Engine runs pretty good for a while but then acts up stops and most often the gas flooding the carb occurs again. Carb is not cracked but there is a tube inside the carb body parallel to the main jet boss. This tube is sealed with a steel ball in the bottom and there appears to be a tube inside that body cavity that the idle screw point runs into when the carb is turned upside down. It's driving me crazy. The engine has alway ran like a top but started acting up about a month ago. Hope someone has a suggestion - aside from buying a new carb that is! Thanks.

First, the 143-696122 model number's not recognizable by the Sears parts site, I oftentimes have to put on some good glasses to discern the number.
Sounds like carb is pretty old from your description, the passage next to main jet boss is the idle passage, which has a metering pin that rattles inside, that's why service manual says to adjust idle needle with the carb upright.
With so much flooding might check oil to make sure gas hasn't entered the crankcase.
To check float inlet needle and needle seat, with carb installed, clamp the fuel line, remove bowl, unclamp fuel line for fuel flow, then exert slight upward pressure on float to see if gas flow quits.
New needle seats are to be bottomed out with groove on one side towards the carb throat.
Make sure the fuel line is good, i.e. not cracked or deteriorated
Jus some things to check.
thanks

In addition to what Glenjudy suggested you may also want to check the float bowl vent, if it's plugged or restricted in any way, it will cause the carburetor to flood as well.

Good Luck.... :thumbsup:

Thanks everyone. The model no. is stamped on the cowling under the electric start switch and there's a hole for a screw where I have the ? mark otherwise, I think the number is right. It's a Tecumseh number. I'm very curious now about the float bowl vent. Can yu describe where that is - I don't remember seeing a vent hole anywhere when I had it apart 20 times!!!! It's 30 deg C below here so I'm not going outside - burr. Goball

Actually, the 143.nnnnnn number is a Sears part number that equates to a corresponding Tecumseh model number, yours is most probably a Tec HMSK80-xxxxxxx(spec no.).
below is service manual covering your model.
http://www.cpdonline.com/692509.pdf
3 to 11 HP 4 cycle L Head
thanks,

check for a possible crack inside where the seat goes, I have actually seen a couple of carbs cracked inside

Can yu describe where that is - I don't remember seeing a vent hole anywhere when I had it apart 20 times!!!!

Inside the float bowl, the vent is covered by a large welch plug that you can easily see when the float is removed. On the outside the vent is usually located on the side of the carburetor that faces out when installed and amounts to nothing more then a small pin hole, however not being able to locate a parts list for your engine, I am only guessing at the type of carburetor you have. The parts manual Glenjudy supplied may be helpful to you in troubleshooting your carburetor.

Best of Luck.... :thumbsup:

To All who replied - Thank you. I reworked the carb again following the advice from you and instuctions in the manual. Can't say as I know what was wrong but the engine runs like a Swiss watch now. Watch out Snow - here I come!! goball