My chainsaw, a Stihl MS441 magnum, over the last year or more has developed a problem of not starting. The local Stihl dealer had the saw for two weeks. After striping the saw down, they handed it back in working condition. They did not know What caused the problem. The good news however did not last for more than a couple of days before it refused to start.
Eventually, I have a sure-fire method to get it started when it refuses to start. I take out the spark plug and blow it dry from the oily sooty liquid. Then I use the air to blow out the oily liquid from the cylinder with the piston up and down position. Then a bit of a blow through the carby.
After putting it together it starts very readily.
There is a lot of smoke for 20 seconds and then normal, very little smoke.
This working stage will last all day maybe many more.
The conclusion is that somehow, the fuel is being 'pumped' into the sump/carby while the saw is not being used??
I have started draining the fuel into a container after I finish each day to see if that will save some work to get it going.
Welcome. Saw is flooding it sounds like. Is it a regular carb model or a cm with computer controlled carb? If it's a regular one then probably need to rebuild the carb. More than likely the needle valve is sticking open and allowing fuel to continually seep by. In an extreme situation it could pool a lot of fuel in bottom of crankcase, but it doesn't sound like that's the case. If it's a computer carb then I don't believe it has a needle valve and a trip to the dealer to have them fix carb may be needed. I haven't worked on any if those myself.
QuoteI have started draining the fuel into a container after I finish each day to see if that will save some work to get it going.
f_r
And does that help?
I agree that flooding is the symptom, but how this happens while the saw is in storage is the question. The carby is not a computer one as far as I know. The fuel tank is lower than the carby so I am wondering how the fuel gets into the crankcase. One possibility is that the daily cycling of temperature and the subsequent changes of vapour pressure in the fuel tank is 'pumping' the fuel through the carby, ending up in the crank case. If that happens the first pull of the starter rope would spread fuel into the rest of the upper cylinder, making it impossible to fire. The carby had been checked by the dealer, but maybe overlooked something. As you say a valve somewhere is not working properly.
The draining of fuel idea is needing several weeks to be sure, but I would be amazed if the fuel can do much while the tank is empty. It is a reasonable assumption that the draining of fuel must work.
Stihl recommend draining the tank when the saw is not being used - a good idea for any petrol engine.
You'd probably know if it was a cm with the computer carb. If it has H and L adjustment screws then it's a regular carb. The needle valve or inlet needle is what let's fuel into the carb. It is opened by the pump diaphragm which pushes a lever down, pulling up and opening the needle. They wear around the point and won't seat properly when worn and can cause the situation you have. Once fuel is flowing, as in running the saw, the flow will continue even after the saw is shut off. Like a siphon. If the lever is set too high it could also keep it open. If you feel comfortable with it pull the carb and open the pump side, should have 4 screws on that side.
The dealer didn't rebuild the carb I'm assuming? That would be where I would start if I were you...it is hard to find a good servicing dealer that knows what they're doing. Once you do, give them business keep em around!
Many thanks: The carby fuel pump system seems to be the target, it does fit the symptoms.
I will have go at it and get back with the result.
Thanks guys