OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters McCulloch Trimmers & Brushcutters Adjusting screws brushcutter

If you followed those tuning instructions when you adjusted the carburetor you should be in good shape as far as carburetor tuning is concerned. I had suspected that you had tried to make trial and error carburetor adjustments rather than following that procedure.
1. If the spark plug has run more than say 15 hours, it probably needs replacing.
2. If it is a foam air cleaner, these normally have to be dampened with engine oil to be effective. However you should follow the manufacturer's directions if you have them.
3. Since your brush cutter was running properly then stopped suddenly, the fuel cap vent becomes a less-likely suspect, but needs to be checked. You also need to look at the fuel pick-up in the tank in case it has become blocked. If there is any sign of sediment in the tank, it needs to be cleaned out and the fuel pickup replaced if it is the strainer/filter type.

4. In general your symptoms sound more like fuel starvation than anything else. Since you also report that the carburetor tuning adjustments seem to have no effect, this suggests that the problem is a fuel restriction upstream of those adjustments. This could be inside the fuel tank, which means the cap vent, or the fuel pickup filter, or the fuel pickup hose could be split inside the tank, or the fuel hose from the tank to the carburetor could be leaking and therefore sucking air. Alternatively it could be a blockage in the first part of the carburetor, which would most likely be in the fine gauze filter at the entry to the fuel pump cavity. Lastly, it could be that the fuel pump diaphragm has failed, so the pump is supplying less fuel than is required. These are all fairly common faults, and fairly easy to fix.