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Stihl 310 Problems

thewoodlands

thewoodlands

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Feb 25, 2015
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New York
I have a Stihl 310 that starts fine but after about 20 minutes of use will stall out or if you let up on the throttle some after coming out of the cut, it will die out.

I took the muffler off and the piston looks good, any ideas on what could be causing this? The saw is either 10 or 11 years old.

The gas in it is new non ethanol and the gas filter is fairly new (two months old) and the saw goes out clean before being used.
 
thewoodlands

thewoodlands

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Feb 25, 2015
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Dose it start back up right away?
No, there are times it won't like it's flooded and there are other times I'll let it sit for about 5 or 10 minutes and try starting it.

I tested the compression after running it and letting it sit for an hour, 140 was the reading after 12 pulls when it stopped going up.
 
thewoodlands

thewoodlands

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@HarleyT , the gas line felt fine and I couldn't see any leaks. I did take the carb off and it looks fine from the outside, the filter and the gas tank were pretty clean after I drain the gas earlier today.

Would it do any good to spray the carb when it's together, I've never had one a part.
 

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thewoodlands

thewoodlands

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Try opening the gas cap when it occurs. The tank vent may be going bad. Easy to check.
I've tried that and it didn't make any difference, I took some air to the vent line too and it was clear without any cracks, the nipple on top of the gas tank the line fits over is clear.

This morning before running it I replaced the spark plug, air filter and some fresh gas mixed 50-1.
 
thewoodlands

thewoodlands

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Likely a bad fuel line.
If you find cracks, or it is soft and gummy,

replace the line and go through the carb.
I bought a parts saw and took the carb out of the 310 and installed the carb from the parts saw and the 310 is running fine, I haven't had any of the problems I had before.

I did buy a carb kit so I can rebuild the old carb, here are some pics from the old carb out of the 310.
 

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thewoodlands

thewoodlands

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I finally took the carb apart and it's soaking in mineral spirits, tomorrow after plowing I'll dry it off and take some air to it. After that I'll spray it down good with carb cleaner,dry it off and take the air to it again.
 
thewoodlands

thewoodlands

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After plowing most of the day, I cleaned up the carb with air after its soaking in mineral spirits for two days. The carb is in the basement and I'll put it together tomorrow.
 
Bfletch

Bfletch

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Possibly. I haven't run it enough to know if it is a problem. I bought a husky 55 closed port, and replaced all fuel lines, muffler gasket, intake gasket, and a carb rebuild. It was fine for a bit,then it started dying after some cuts. And they weren't very big trees. Like 6 inch
 
Old2stroke

Old2stroke

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The 2 "copper" things are actually brass check valves. The one down in the recess is the main jet nozzle check valve and the other one is usually in the fuel supply path to the low speed circuit (usually only found on saws with a primer bulb). The main one is easy to replace by punching it right through into the carb throat and can be repaired (do a search for repair thread). The other one is damn near impossible to remove without destroying it. The essential internal part of these valves is a small rubbery disc that is often destroyed by blowing the carb out with high pressure air. Both of these valves can cause erratic engine behaviour when they go faulty and are never included in a repair kit. The main nozzle valve is essential but the other one can usually be left out with no effect on the engine except the primer bulb will no longer be effective, if it has one.
 
Old2stroke

Old2stroke

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Going back to look at the carb pics, it looks like the saw does have a primer bulb, so an easy way to partially test the check valves is to block the fuel input port and apply a vacuum to the primer port and see if it will hold a vacuum. This will test if the valves are closing properly but will still not test if they are opening fully. These frustrating little beggars can pass lots of testing but still be erratic in operation so the best solution if they are suspect is to replace them. They are cheap but you have to buy them from someone who can supply Walbro parts and usually they have to be ordered, which means waiting.
 
thewoodlands

thewoodlands

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Feb 25, 2015
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Going back to look at the carb pics, it looks like the saw does have a primer bulb, so an easy way to partially test the check valves is to block the fuel input port and apply a vacuum to the primer port and see if it will hold a vacuum. This will test if the valves are closing properly but will still not test if they are opening fully. These frustrating little beggars can pass lots of testing but still be erratic in operation so the best solution if they are suspect is to replace them. They are cheap but you have to buy them from someone who can supply Walbro parts and usually they have to be ordered, which means waiting.
Thanks @Old2stroke , for some reason they took out the carb that was in the saw and put this carb in, the 310 doesn't have a primer bulb. Two shops told me the original carb was good but I kept having problems after 20 minutes of running it. I did get a parts saw for $41.00 dollars and I put that carb in the 310.....it's been running fine since then.

Cleaning and rebuilding the old carb is something new for me so if it doesn't work, we still have the other carb that works fine.

The 310 pissed me off enough that I went and bought a 311 :) the wife thought that since I had a new saw that the 310 problem was behind us! :lol:
 
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