Homelite chainsaw carburettors come with adjustable low- and high-speed screws, which allow you to control the amount of air mixing with the fuel at high and low speeds. While the carburettor's low and high limits are factory-set, for safety reasons, over time, and after a carburettor cleaning, you'll need to adjust the screws to ensure optimum performance of your chainsaw. Improper adjustment of the screws can damage the engine, so you should not undertake this operation without the proper equipment and knowledge.
Open the cylinder cover with a screwdriver. Remove the air filter and clean it by hitting it against your palm and wiping off as much dust as possible with a rag. Replace the air filter if it's very dirty. Wipe the area around the filter with the rag. Open up the front of the muffler with the screwdriver and remove the spark arrester screen. Clean the muffler and screen with the rag and brush.
Fill the chainsaw tank with freshly mixed chainsaw fuel. Start the chainsaw and let it run on a high idle for five to 10 minutes to allow it to warm up to operating temperatures. Do not adjust your carburettor on a cold engine.
Turn the screw marked "Lo" to the left and note the effect on the engine. Stop turning the screw once the engine starts to whine. Turn the screw to the right and note the effect on the engine. Stop turning the screw when the engine starts to bubble. Move the screw in between the two settings to achieve the optimum setting. This will take practice and a good ear to discern the cleanest, smoothest engine sounds.
Set the idle speed screw by adjusting the screw marked "L." Use a tachometer to reach an idle speed of 2,800 to 3,200 RPMs. Turn the screw to the right, if the chain starts to spin when idling. The chain should never spin when idling.
Set the high speed screw by adjusting the screw marked "H." Pull the trigger so that the throttle opens as wide as possible. Turn the screw to the left and note the engine performance. Stop turning the screw when the engine starts to make a high-pitched whine. Turn the screw to the right and note the performance. Stop turning the screw when the engine starts to bubble.
Test the maximum engine speed without load using the tachometer. The engine speed should read about 11,500 RPMs but never should exceed 12,000 RPMs. If the engine exceeds 12,000 RPMs, immediately let go of the throttle and adjust the high-speed screw back one turn, counterclockwise, then again test the engine with the tachometer.
Over-tuning of the high-speed screw above 12,000 RPMs will damage the chainsaw engine.