Small Engines (Lawn Mowers, etc.): Carburetors, zama, air compressor

Question
Hello Eric,

I am working on a briggs 42A700 series carburetor. It will only run with the choke closed at about 85 percent. Running lean or a passage is blocked but I'm not sure. When I open the choke further the engine starts hunting, surging and oscillating.

So you feel that ethanol can harm the metal or plastic parts of ANY carburetor? It seems like I come across a lot of carbs that will only run with the choke on or set to some degree. If the choke is off the engines runs rough or just dies.

What is a good source for learning about little carburetor such as ZAMA and Walbro? I have a ZAMA were it seems that the primer won't operate as if something is wroning with the white primer base beneath the primer bulb like it is clogged up.

Thank you.
Vince

Answer
Walbro carb link:     http://wem.walbro.com/distributors/

Zama link:         http://www.zamacarb.com/tips.html


For the larger 42 cubic inch block that is running lean I would recommend cleaning it with compressed air from an air compressor.  Blow compressed air through all the carb orfices.  If it still does not run correctly then dis-assemble again, remove all plastic parts and soak in carburetor cleaner over night.  Clean with parts cleaner and blow compressed air through all the carb ofices again.

I have to clean some carbs 2 or 3 times to get them clean.  If the carb is still running lean you can always use carburetor drill bits and make the jet orfice larger.  If you make it too large you can alway fill with solder and start over...if you remembered to measure the orginal size of the jet before you started messing with it.

Eric