We get a lot of calls from people that have
"adjusted their carburetors to death",
hoping for that magic moment when it all comes
together and runs perfectly...
here is how you fix what you have adjusted.
On most carburetors,
to help find the correct adjustment,
there is a small "L" beside the Idle
mixture screw and "H" beside the
High speed mixture adjustment.
Normal adjustment for 2 needle carburetors begins with the L needle. This adjustment controls the fuel flow to the low speed or idle circuit. If the carburetor is too far out of adjustment to run, or has been disassembled, start with turning the L and H all the way in and then open 2 turns on each needle. Then turn the "TAS" screw or idle speed adjustment in all the way.
When turning any of these screws be careful not to over tighten,
this can cause damage to the carburetor and / or needle.
Now you are ready to begin adjusting.
Start the engine and allow it to warm up for a few minutes. Do not try to adjust the carburetor before the engine warms up as settings change while the engine is warming up. Begin with the L needle, turn the needle in clockwise and listen to the engine as you do so. The engine will speed up to a point then start slowing down again, the point of the highest speed is called optimum. This is at the most efficient point for the engine to run. When you find and set the engine to this point then adjust the TAS or idle speed screw. This screw adjusts the idle speed, you should try to adjust it so the clutch is not engaged or ringing.Note: when the clutch disengages the chain or string will stop moving.Some string trimmers do not have a clutch, so adjust these engines to a steady reliable speed. Once you have adjusted the idle speed it is necessary to recheck the L screw adjustment for the optimum point described above. It may be necessary to repeat these two adjustments several times to get the engine to run correct. The L screw may be opened 1/8 to 1/4 turn from this optimum point to help the engine to accelerate well to full throttle.The high speed adjustment procedure is similar to the "L". Accelerate the engine to full speed and search for the optimum point as described for the L needle. The important part to remember about adjusting the L or H screw is not to let the engine drop much onthe lean side of this point, (screw in) you want to find the highest speed when turning the needle. However going too far past this point may result in engine damage. As with the L adjustment the H needle may be richened a little, but no more then ¼ turn from optimum point.
 |
If your carburetor has no slots for a screwdriver, as in the picture, it is adjustable "only" (see note below) with a special screwdriver available from the original equipment manufacturer. Most manufacturers only sell these to dealers. |
SHADE TREE NOTE:
(and you didn't hear it from me)
A small dab of "crazy glue" on a small nail head can often be fused to the tip of the adjustment screw to give you enough leverage for adjustment. Clip the nail off with side cutters when finished.
Still no luck? There is a good chance that either you have poor quality fuel, or a defective (read "Bad") Carburetor and further steps are needed. Replacing the gaskets and a thorough cleaning (putting a" kit" in it) is the next logical step, but still may not fix the carburetor.
 |
Carburetors with white scaly metal (white rust) inside don't usually heal with a kit and need replaced. |
