Two Stroke Engine Troubleshooting
Are you having problems starting your two stroke engine, and keeping it running if you do get it started, I have found that almost always the problem is with the carburetor. If you do get it started, and even after trying to adjust the hi and low rpm needle valves, and you still can not keep it running properly, it is definitely the carburetor. This problem can occur with any make of small engine equipment, some of which are Echo, Stihl, Shindaiwa, Homelite, Husqvarna, Sears, etc. Some of the types of equipment involved could be a chainsaw, weed eater, leaf blower, hedge trimmer to name a few. The main cause of this problem is stale fuel which is caused by improper long term storage. If a fuel stabilizer is used when the piece of equipment is stored for the winter or more than sixty days, this problem could be avoided. Or better yet, fuel stabilizer should be added to your fuel mixture every time a new mix is made. What happens is that the diaphragm inside the carburetor has been hardened by the fuel that is sitting in the carb while it is being stored, the diaphragm is not pliable anymore. This diaphragm acts like a float in a four stroke carburetor. When the engine is being started there is vacuum created which pulls on the diaphram which pushes on the metering lever which in turn pulls open the metering valve, and once the diaphram has hardened it cannot move to the full open position and let enough to fuel through the metering valve. The engine is starved of fuel which causes the hard starting and erratic idle and erratic high speed rpm. The simplest and cheapest solution is to install a carb kit. The kit costs about $15.00 to $20.00 CAD and takes about half and hour to install if you are mechanically inclined. Also while you have the carburetor apart, you should clean it with a cleaning solvent. A more expensive way is to get a new carb which would be easier and quicker to install than a carb kit.
After installing a carb kit and reassembling the piece of equipment you will have to adjust the carb. On most two stroke engine carburetors there are two adjusting screws, one is marked with a H and the other is marked with a L. The H is for high rpm (Main mixture) and the L is for Low rpm (Idle Mixture). First turn in both screws all the way in and then turn them both out 1 and a half turns. Pump the primer bulb if the equipment has one. Start the engine, once it is idling, turn the L (Idle Mixture) screw out (counterclockwise) from the preliminary setting until the engine speed decreases (rich). Note the position of the needle. Now turn the adjusting needle in (clockwise). The engine speed may increase, then it will decrease as the needle is turned in (lean). Note the position of the needle. Set the adjusting needle midway between the rich and lean settings as in the picture below. Don't touch the throttle during this procedure. Once you have found the best idle speed for the engine then you need to adjust the high rpm. This process is the same as with the idle rpm process but you need the to hold the throttle wide open while you are adjusting the H (Main Mixture) needle on the carburetor.
WARNING Read operator's manual for safety instructions before you attempt to troubleshoot. Use extreme caution when troubleshooting power equipment. Never start or run power equipment inside a closed area — breathing exhaust fumes can kill.
Also See Proper Two Stroke Oil Fuel Mixture Ratio and Carburetor Troubleshooting Chart. See Step by Step Two Stoke Carburetor Rebuild to learn how to rebuild a two stroke engine carburetor. Visit our Help and Tips Forum to ask any troubleshooting questions. Visit our new Repairspot FAQs Page. Back to Help and Tip Need a new or used small engine manual? Search abebooks.com
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