Small Engines (Lawn Mowers, etc.): craftsman backpack blower, carburetor body, adjustment screws

Question
I have a fairly new, used about 10 times, 30cc craftsman backpack blower model 316-794991 that has a problem with the engine speed changing even though I am trying to run it at full throttle. I can't locate the users manual and it appears there are no adj. on the carb. What might be causing this problem and how can I fix it?

Thanks,
John Petelle

Answer
If you are talking about surging where the rpm's go up and down for seemingly no reason and sounds like the blower is running out of gas.  Two things will cause this one a two cycle engine.  They are lean fuel conditions or an air leak.  Lean fuel conditions means, just like it sounds.  The engine is running lean for some reason.  Typically this is caused by a dirty fuel system and would require thoroughly cleaning the fuel system.  Start with the fuel cap and clean the vent.  Then clean out your gas tank and back flush, where the fuel comes out.  If there is a fuel filter, replace it fuel should flow freely to the carburetor.  Then the carburetor would be removed and completely disassembled.  Use a wire from a twist tie clean every air and fuel passage in the carburetor.  If there is a Welch plug in the carburetor body.  It should be removed and fuel passage behind it cleaned.  Blow out all passages with carburetor cleaner or compressed air.  Reassemble carburetor using new carburetor kit.  The adjustment screws could be covered by some silicone.  Remove the silicone when disassembling the carburetor.  Replace the adjustment screws and lightly seat them.  Turn each out about two turns.  Reattach the carburetor using new mounting gaskets.  Attach fuel and primer lines throttle and choke cables.  But fuel and the fuel tank and start the unit as you would normally start.  Let it run and warm-up for about four or five minutes.  The adjustment screws can then be adjusted with the throttle at wide-open turn the high-speed screw in until the engine starts to starve and then turn it out until the engine starts to flood.  Set it halfway in between.  The idle screw is set the same way, but at the idle.

The other condition that will cause surging is an air leak.  An air leak can be a leak at any gasket surface.  Check carburetor mounting and the insulator block the carburetor he usually wants to.  This insulator block can sometimes work or crack so inspected also.  Check air filter assembly gasket for air leaks and inspect carburetor throttle shaft for wear.  Check cylinder head screws to be sure they are tight and crankcase halves screws to be sure they are secure.  Crankshaft seals should be dry and if not replace them.

Try these two methods of troubleshooting to see if you can resolve your issue.  And if not please get back to us.  I hope this information helps good luck on your project.