Sears 20" chainsaw starts won't stay running...Help!

mortensenalJune 5, 2013

I have seen all the messages regarding chainsaws that start but don't stay running. I am in the same boat. I have a sears 20 inch chainsaw (358 351200). I have replaced all of the fuel lines, the fuel filter, the spark plug and have installed a brand new walbro carburetor. The chain saw starts, idles smoothly and will run at high speed initially. Once the chain saw gets up to speed, it will die after about 20 seconds. I am able to start the saw again after choking and pulling 2 or 3 strokes, but the same thing happens. I have gapped the plug, cleaned the air filter, changed the fuel and am at wit's end. Any recommendations?

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Possibly a vacuum in the fuel tank or a lack of fuel is restricting fuel IMO.

1. Open the fuel cap enough to know it is getting air.

2. What are the Approx fuel mixture screw turns from a light seating?

3. Give some history on the saw and when this started before the new carb.

4. Two cycle engines are so temperamental, they are retiring me to electric saws etc at home vs away.

    Bookmark   June 5, 2013 at 7:50PM
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I don't know how long you mess with it? IMO once you replace the fuel lines ( and carb.) takes awhile to get all the air out of the lines and carb. I would get it started rev it up and use some carb. cleaner down the carb. venture see if that allows it to stay running and hopefully work any air that may be trapped... After you do this several times and still no luck I would make sure the filter on the end of the hose in the tank is not restricting gas to be pulled up. revisit carb. installation making sure the gasket not partially blocking any small passages.

Point brought up by loger the carb. maybe too lean when the saw begins to warm up. Half choke should help in this case.. Don't know your expertise with two cycles when it comes to adjusting carb.

    Bookmark   June 5, 2013 at 9:11PM
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I have used and tuned lots of two cycles over the years. I get no lag when i accelerate from idle. Idle is slow enough to prevent chain rotation and still purr. problem is that even with new gas and vent lines I'm not getting consistent fuel flow apparently. I have ordered new check valves. That is the only part that I Have not checked. I even went so far as to remove the vent plug (porous metal filter on end of return air line) and that didn't change the problem. I suspect it is the check valve because when I open the fuel tank I find that the system doesn't cut off.

In case anyone is going to say something about the exhaust, I have run this saw pretty cleanly so there is absolutely no carbon buildup on the muffler (BTW, it would take one heck of a lot of rich fuel operation to foul a significant percentage of the muffler screen - speaking of this as a likely problem is a real red herring).

    Bookmark   June 7, 2013 at 10:43PM
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