some useful info i found about tuning your jiffy, hope it helps someone.
picture of carb set-up
First change the spark plug and have fresh gas w/correct oil ratio.
The most common carb used on augers are the Walbro.
They all have a fuel pump which consists or a body and diaphragm. Thereís a port goes from the carb through the gasket and into the crank. As the engine is turned over it sucks and blows though that port, in turn moves the diaphragm. That diaphragm can get stretched out or breakdown, in either case it can't pump the fuel like it should.
Thereís also a gasket in the carb stack that has little flaps, those flaps allow gas movement in one direction. Those can go bad too.
Next is the fuel inlet valve, It opens and closes the flow of gas going into the carb determined by the fuel level.
Itís held in place and hinged on a fulcrum with an adjustable tang. That tang adjusts the fuel level in the carb.
With a float/bowl carb you adjust by the float drop but we're talking about a carb without a float & bowl right now.
In our case the tang should be level with the carb body.
If you look, the center of the pumps diaphragm will come in contact with the inlet needles tang. In both cases, float & bowl or bowless carb, The tip of the inlet needle can become damaged and either stick in place or become damaged enough to where gas will seep by when it should be closed.
So say your auger isn't running right and you take the carb off and clean it. You should buy a carb kit and replace the gaskets, diaphragm and inlet valve and seat too.
Not all Walbro carbs are the same. Some use both Low speed and High Speed mixture adjustment screw. Most times you can adjust the mixture to get the auger to run at its best but not if the diaphragm or valve/gaskets are bad.
Some and most new engines have internal jets. You'll have to take that carb apart to clean and replace the diaphragms and clean the jets. The jet is made of brass, its inside diaphragm is tiny so it doesnít take much restriction to effect how the auger runs. Brass is also soft so don't enlarge the hole when you clean it.
Some augers with the fixed main jet will benefit from replacing that jet with a larger jet. I did just that with my Nils. Your auger might benefit from that too. Modern small engines have to conform to EPA standards. Itís impossible to get peak performance out an engine that has to meet those standards in cold weather conditions.
Normal operation was a good warm up till the auger would cut. Now you should warm any engine up before putting a load on it but the warm time up required for the Nils seemed extreme. Once warm though it cut like no other auger.
I went from a .37 to a .38 main jet. End result, no long warm up times and more power when under load. I'll get into that mod with pictures at a later date.
Back to the tune up.
This will be for the Walbro carbs with the High and Low Speed mixture. Your carb will have an L and k stamped into the carb body. Thereís also an idle speed set screw.
Let the engine warm up. Start with the Low speed mixture. Turn it in (clockwise) till the engine starts to run high and or slow down. Now turn it out till the engine runs at its highest RPM. You can go in and out to get it at that point.
Once you get Low speed adjusted so the engine run at its highest/smoothest point you turn the screw out till it starts to just slow down. Why wouldn't you leave it where it runs at its highest point? Because itís running lean there and will be hard to get started. Turning out will richen the mixture so you won't have to pull on the rope more then a couple times to start it.
Now you have to adjust the High Speed. This should be done under load/cutting ice. Adjust till you get to the point of max RPMs and then again turn the screw out till it you notice the engine slowing down. Do that and you won't be running lean; Running lean will burn an engine out. Thatís especially important if you like drilling a series of holes one after another.
Basically there are 3 adjustments to a carb. Idle speed- is a simple stop screw on the external linkage to set idle speed.
Low Speed Adjustment- this will meter the gas/air mixture inside the carb.
High Speed- this will meter the gas/air mixture at high speeds.
Turning in - Clockwise = lean
Turning out - Counter Clockwise= Richen.
If the won't run without having to prime or without giving throttle you are too lean at Idle Speed. You want to richen that mixture.
At high speeds if the engine won't run without priming you'll need to richen that adjustment.
In an attempt to make small engines friendlier, we start seeing limiter caps on High and Low Speed adjustments or no adjustments at all and fixed jets are used.
If this is a problem that has just started then you should look into having the carb cleaned and rebuilt.