Seals and or rings would not make the saw rev high. More likely the throttle is sticking open after it gets hot. Check throttle position and clean. Get a can of spray carb cleaner from auto parts or the marine store. Spray away till it’s clean and check the throttle position again. RPM’s only go up for two reasons, and they are both fuel air ratio. One is the throttle is open the other is momentary rev when the fuel supply is cut off.
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The carburetor regulates the ratio of air and fuel that enters the engine. If extra air enters the mixture after the carburetor, the ratio will become lean, which will increase the engine RPMs. This air can enter through the gasket on the carburetor if the gasket it loose or damaged.
The carburetor might be clogged. A clogged carburetor is often caused by leaving fuel in the chainsaw for a long period of time. Over time, some of the ingredients in the fuel may evaporate, leaving behind a thicker, stickier substance. This sticky fuel can clog up the carburetor and cause the chainsaw engine to stall.
The fuel line may be clogged from stale fuel deposits, more reasons to cause your chainsaw to cut out when applying throttle. If a fuel line is cracked, it will leak gasoline and draw air from outside into the fuel line. If the line is leaking fuel, it needs to be replaced.
The two most common reasons a chainsaw won`t idle are a blocked air filter and an idle screw out of adjustment. Other possible causes include: Dirty Air Filter. Idle Screw out of Adjustment.
Chainsaw Chain Keeps Moving at Idle –
FIX A – Faulty Clutch Either replace you clutch, clutch spring, or tighten the spring. There could be lots of sawdust or wood chips stuck in the clutch, if so get rid of this.
If your chainsaw bounces around when making contact with the wood, it means that that chains teeth are not grabbing on and ripping through the wood. A sharp chain will cut in a uniform and straight line.
Generally, two-stroke chainsaw engines are built to conveniently run at full throttle without an engine breakdown. Therefore, running at any throttle speed below the full throttle is not advised. Cutting a thick wood or timber while running at a low speed or throttle can cause the blades of the chainsaw to become dull.
The carburetor might be clogged. A clogged carburetor is often caused by leaving fuel in the chainsaw for a long period of time. Over time, some of the ingredients in the fuel may evaporate, leaving behind a thicker, stickier substance. This sticky fuel can clog up the carburetor and cause the chainsaw engine to stall.
The carburetor might need to be replaced.
It could be damaged or old and no longer functioning. To test the carburetor, remove the air filter, pour a teaspoon of fuel into it, and pull the starter rope. If the engine starts momentarily and then dies, the carburetor is likely why the chainsaw won`t start.
To fix the problem, start by
draining the gas tank. Replace the old gas with a fresh mix of gas, being sure to add a stabilizer to keep the ethanol from gelling. Often, just getting fresh gas and stabilizer through the chainsaw`s fuel system may correct the saw and it should stay running.
Most commonly either the fuel is stale or mixed incorrectly or incorrect oil. Next is maintenance of the unit, air filter restricted, spark arrestor, carburetor adjustment. Improper use of the equipment not running at WOT (Wide Open Throttle) or overloading (Lugging) of the unit.
Generally, two-stroke chainsaw engines are built to conveniently run at full throttle without an engine breakdown. Therefore, running at any throttle speed below the full throttle is not advised. Cutting a thick wood or timber while running at a low speed or throttle can cause the blades of the chainsaw to become dull.
If your chainsaw is vibrating excessively, you should locate your rubber bushings where they connect the engine to the handle. It should be somewhat obvious that the rubber bushing has worn down, and if you notice this has happened you will need to replace them.
Chainsaw stalls Chainsaw is 4 years old and has a history of moderate use. After I ran the saw about 1 minute on plain gas (grabbed the wrong gas can – ouch) the chainsaw sputtered and stopped.
It didn't seize, and the pull starter never became more or less difficult than normal. The engine would continue to start if I pressed the prime bulb and engaging the choke, but stall again after 10-20 seconds. The temperature that day was about 50 degrees F and I was running the saw with the “cold plug” installed (per warm weather running).
When it refused to keep running I did the following:
Flushed the fuel tank (that's when I saw the gas had no oil in it).
Ran hardware wire through all of the fuel lines.
Replaced the fuel filter and spark plug.
Cleaned the air filter with a nylon brush and compressed air.
Same behavior (start then stall in less than 20 seconds). I made at least 20+ attempts to start it.
I removed the carburetor and, though it looked perfectly clean, I took off the top and bottom covers then sprayed everything with automotive carb cleaner and blew out the passages with compressed air. The gasket and diaphragm looked new. No pinholes in the diaphragm when held against a bright light. I reinstalled the carb but got the same behavior (start then stall in less than 20 seconds). I again made at least 20+ attempts to start it.
I disassembled the short block and saw that the piston has some slight scoring on it. The ring is clean and I verified that the piston ring has .001 clearance between it and the piston ring groove all the way around with the ring held tightly in place (I was thinking that the piston might have become deformed if it did indeed get too hot when run without any oil premix).
The cylinder wall has no scoring and there isn't any signs of melted aluminum anywhere. The crank is clean as was the inside of the crank cover.
I reinstalled the crank cover using permatex non-hardening gasket goop and torqued the cover bolts to 10 inch pounds. I reassembled everything else per the exploded diagrams in Echo's “parts manual” for the CS400.
During assembly I took note that both the carb gasket and intake boot look like new.
Still the same result: press prime bulb once, engage choke, pull a few times and it starts but stalls after 10-20 seconds.
I'm stumped.
ANSWER : Not sure what to say other than its fuel starvation, if not already done replace the fuel filter in the tank, if no better i would suspect a massive air leak, so replace the crank seals, if there is no primary compression in the crankcsae fuel will not pull through the engine, good luck.
