Chainsaws

Hi Tommy. It is a high probability you have a timing issue. You started with good basics for an engine requiring spark, fuel, and compression. I do not have direct experience with the Mac10-10auto. However, we can take what you have done with those three basics and move closer to a solution by taking each out to the next step for spark, fuel, and compression. You probably tried some of these already.

Spark: You said it has a good spark Things that could still affect ignition that are spark related could be: Is it the right plug? Is the plug gaped to the correct specification? Is the plug torqued into the engine correctly? Is the plug firing at the correct time? You probably did the first three already. If you have a great spark, in good fuel, in a properly compressed environment, but with no ignition then the engine is probably not timed correctly. That spark has to occur when the piston is close to top dead center (all engines vary slightly). For example, if the piston is coming half way up on the compression stroke and there is weak ignition right then, the operator could easily misinterpret a weak ignition as good compression. Without knowing the specifics of the Mac10-10auto, I recommend you acquire a manual for this engine. For your engine's timing you probably have a key that keeps the flywheel correctly positioned with respect to the crankshaft. If the key, shaft, or flywheel become damaged where the three come together it will affect the timing. If the key is steel the damage will usually be to the flywheel. If the key is aluminum the damage will usually be to the key. Inspect the contact surfaces where the three come together for any sign of sheering damage. Even the slightest dent to the aluminum key can inhibit timing enough to prevent ignition. If damage is found, replace the damaged component or components. I saw the comment about using your electric drill. You also need to check for good spark while using the dill. Some drills, when used on some engines, do not rotate the engine fast enough to generate a spark. You also need to make sure you smell fuel/oil mix coming out the exhaust since it is not igniting. The fuel has to go somewhere and that should be out the exhaust port. If no fuel/oil mix is coming out the exhaust that means the engine is running dry, and you should stop drilling/spinning the engine until you fix the fuel problem. I use a drill often when checking old engines, it is a smart man's electric starter that works great.

Compression: You said you have good compression. Some saws work on as little as 40 psi, of pressure and some will not work if the pressure falls below 90 psi. So the issue is whether you have at least the minimum compression that your engine is designed to run with. To identify your engines exact compression you need to use a compression tester. You also need a manual or reference to identify the compression required. Once you know the compression required and if you do not have that much compression you may need to check for froze rings, damaged rings, damaged or scored cylinder walls, like Roger B recommends. Before you test for compression you need the correct fuel/oil mix in the engine. The fuel/oil mix you use will affect the engines compression. More oil in the mix gives you more compression.

Fuel: You probably did everything necessary here to get ignition. Is it the right fuel? Is it the right oil? Is the mix correct for that engine? Is the fuel/oil mix fresh? Is the fuel/oil mix getting to the compression cylinder in the right ratio to air (it needs a particular ratio of oxygen)? You mentioned you even tried pouring fuel into the cylinder. You probably took care of these already and we are only talking about ignition at this point and not sustained running. Sustained running could require much more than what is covered here, for example, gaskets, and carb adjustment/cleaning/rebuilding like Roger B., recommended. Caution: the use of starting fluid in a two cycle engine can easily and very quickly cause significant wear and damage to the engine. Engines ruined with starter fluid are called “Ether Baby” for a reason. The starting fluid almost immediately washes the engine of the oil that protects the rings, cylinder, rod, crank, bearings, and wrist-pin, and damage follows shortly. Additionally as the oil is washed/evaporated the compression drops dramatically even prior to ring, piston, and cylinder wear. It is possible you have not yet damaged the engine significantly because of the low rpm the engine is at during your starting attempts.