Chainsaw Repair
Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Stihl => Topic started by: bassman on February 06, 2013, 11:11:56 am
-
i havea Ms460 that starts and runs for about 5 seconds then dies. I havent replaced the diaphrams in the carb. they
seem to be ok. Could the carburetor be faulty?
-
The metering diaphragm can cause erratic fuel mixture problems because it is stiff. The integrity of the diaphragm will be complete but the carb will not work correctly.
-
I would look for ragged sucking tube between cylinder and carburetor or impulse tube.
-
I did a pressure check on the saw and found no leaks. When the saw quits it will start right back up again. Runs great for a few seconds. Its like someone shuts the switch off.
-
A stiff main diaphragm can often get the saw started but very quickily run itself out of fuel once the thing is running .Because of being stiff it's capacity to hold fuel is diminished .
Fact just today I had a very similar situation on a 2 cycle snow blower .The thing did have electric start which saved my arm .I set it extremely rich where it would idle and blow black smoke .After a while it had limbered up the diaphragm enough it would run under normal conditions .I'll bet it took a dozen -15 restarts and ten minutes of running before it healed its self .
-
With the choke closed, the engine itself can suck fuel all the way through a carburator regardless of the metering diaphragm but the carb will not function on its own because of a bad pump valve or a stiff diaphragm.
-
I put new diaphrams in the carb. It still starts then dies. I am soaking carburetor again and see if that helps. Im thinking carb might need replaced. Thanks for your help. Any other ideas , Im all ears.
-
You may have trouble with the impulse line or path or a hole in the impulse line
There may be a hole in the fuel line
Or the fuel filter may be plugged
-
It's probabley a better practice to change all the soft componets of a the carb instead of just the main diaphragm providing you have them all .Usually if the main gets stiff so are the fuel pump checks .
Now I'll admit I've gone through my pile of junk a time or two and found some componets that did work but they were short lived .
-
It's probabley a better practice to change all the soft componets of a the carb instead of just the main diaphragm providing you have them all .Usually if the main gets stiff so are the fuel pump checks .
Now I'll admit I've gone through my pile of junk a time or two and found some componets that did work but they were short lived .
I agree, sometimes changing the all the carb compenents could fix it.
-
Here is what ive done so far. Cleaned carb. 3 times, checked fuel line and filter,vaccum tested the crank case and fuel tank, replaced both diaphrams,and put new spark plug and fuel. So far no change. Also presssurized crank case.
-
Wish I could help you but big Stihl's hate me. I've had 2 MS440 and a MS460 do the same thing to me. MS460 I replaced everything but the cyl., crank and bearings and I still couldn't get it to run. Had 5-7 hrs labor in it gave it back to owner for cost of parts. This saw is the only thing I have ever had beat me. Back is too bad to pull on em. My helper left caught him stealing from me.
Shep
-
What does you needle valve lever look like? It should be level. Did you replace you valve needle? Replace all your welch plugs and cleaned the ports going into them?
-
i put a new needle valve in and made sure every thing was set right, removed welch plug and cleaned. No luck. I could have built a new saw faster. I think Farmboy has a good idea, eat the labor and give it back. I need to know why it wont run, its killing me. Thanks for all your suggestions, allways can learn from others.
-
Finally, I put a new carb. on the saw and now it runs fine. Thanks for everybodys input.
-
I had this very experience with an 8 hp Briggs shredder motor once. Put in a rebuild kit, took it out, put it back in. Cleaned everything a half-dozen times. I never could get that thing to settle in. Finally, bolted on a new carb and it ran like a champ on the first pull. Learned my lesson.
-
Glad you got it going
-
Thanks everyone. Its good to have guys like you all to come to for help.