I had the same problem and was able to fix it by tightening the two allen-head screws holding the cylinder to the crankcase. These screws had vibrated loose and was letting air enter the combustion chamber causing the mixutre to be too lean to run. This does require some disassembly but the entire job only took about 30 minutes.
How to Identify and Fix Common Gardening Problems ?
We provide a variety of viewpoints on how to identify and fix common gardening problems. Our sources include academic articles, blog posts, and personal essays from experienced gardeners :
When your trimmer starts and runs on choke, it could be because the check valve in the gas cap is clogged. Start the trimmer and gently unscrew the gas cap halfway off. Turn the choke off and assess. If the engine is still running, that means the gas cap may be the culprit.
Why would the engine only run while the choke is on or with repeated manual priming? An engine that requires the choking (partial or full) after initial engine warm up is an indication that the engine fuel air mixture system is out of adjustment.
If your trimmer engine idles, but stalls on throttle, check the following parts: the gasket, primer bulb, fuel filter, air filter, fuel vent, fuel line, and carburetor. The repair and symptom guide will help you better identify the part needed to be replaced and how.
Why Does Your Lawn Mower Only Run With Choke On? Your lawn mower only runs with choke on because of a problem with the engine fuel-air mixture system, which can be caused by the carburetor, bad fuel, or air leaks. The choke compels more fuel in the combustion chamber to help the engine to turn over when cold.
If your bike is only running with the choke on, it`s probably because it`s running too lean. This can be caused by a few different things: All internal combustion engines need three things to run: fuel, air, and spark. If any of these are missing or not working properly, the engine won`t run.
An engine that will fire and run with the choke closed but dies when the choke is opened likely has debris at least partially blocking the fuel passages in the carburetor. In this condition the closed choke provides enough extra fuel to enter the engine to overcome the lack of fuel flowing through the other passages.
A choke valve/cable is designed to restrict the flow of air in the carburettor of an engine. This helps enrich the fuel-air mixture, improving the ability to start an engine in low temperature conditions.
If the engine is not revving up and cuts out before you reach higher revs then you need to do the following checks: Fuel: Make sure it is fresh and correctly mixed (see `Starting Issues`). Air filter: Make sure it is clean and unclogged. Fuel cap: Make sure it`s hand-tight.
A clogged fuel filter is most commonly caused by leaving fuel in the string trimmer 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 fuel filter and cause the engine to stall.
A snowblower that runs better on half choke likely suffers from a dirty or faulty carburetor. Cleaning or replacing the carburetor will fix the issue.
If the choke does not close, then either the linkage is gummed up, the air horn is warped, or the spring tension is too loose or the choke spring has experienced a failure such as an internal break.
If the choke does not close, then either the linkage is gummed up, the air horn is warped, or the spring tension is too loose or the choke spring has experienced a failure such as an internal break.
If the choke does not close, then either the linkage is gummed up, the air horn is warped, or the spring tension is too loose or the choke spring has experienced a failure such as an internal break.
If a motorcycle or ATV only runs with the choke on, it`s because the richer “choke on” mixture is actually closer to the engine`s normal operating fuel mixture than the leaner “choke off” mixture. So when the choke is turned off, the engine gets too little fuel and too much air for it to run and it stalls.
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.
