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MS310 4-stroking under load

RD35

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Hello folks! Need some expert opinions. I just finished doing a re-build on an MS310. New piston, cylinder, crank bearings, seals, and muffler. Disassembled and cleaned the carb while I was at it. So, put it together, poured some premium premix in the fuel tank and some chain oil in the oil tank. 3 pulls and it was running. Did a little teaking on the carb and had it running nice and smooth. Burped the throttle at low RPM's for a couple of minutes just to be sure everything was getting a good coat of oil. Then I started doing test cuts. So here's where it started getting wierd. Saw revs nice and crisp...no misses, no pukes, just nice response. Idles fine. When I rev it up and start cutting it runs great for about 2 seconds as I begin cutting through the log. When I push down and load the engine hard it starts 4-stroking and when I lift on it to relieve the load it struggles to speed up but then comes back to life and revs fine. I first thought it was too lean which I very quickly corrected by backing out the H jet. This seemed to have no effect except that it would 4-stroke with no load at a much lower rpm and was weaker. After about 5 minutes of cutting as the saw came up to full temperature this issue stopped happening and it cut just fine.
Any idea what might be happening with this saw under load when it is first started?
 

RD35

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Thanks T.Roller! I guess I just never had set one overly rich before. At least I wasn't running a risk of under-lubing the new P&C.
 

T.Roller

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Thanks T.Roller! I guess I just never had set one overly rich before. At least I wasn't running a risk of under-lubing the new P&C.
That is true! Make sure you have a good sharp chain to start with. It should 4 stroke with no load but as son as you put it in wood it should clear up. You can make about a half cut then hold it up a bit and check for 4 stroking off load then dig back in.
 

RD35

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Well....I went back and started over on my initial settings. (And this time I didn't go an extra half turn rich). Fired it up. Small tweak. Runs great. Thanks again T!!!
 

smokey7

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Old thread but well worth noting 1/2 a turn extra is a huge adjustment on a small engine carb. They react very quickly with small adjustments. 1/8 a turn richer is easily up to 1000 rpm change. So 1/2 a turn from a proper adjustment richer is likely going to take it from 12500 to 8000 rpm no load and be running 6000 on cut. Which severly handicaps the saw and makes them very sluggish fuel guzzeling pigs. Nice job fixing the saw and hope your rebuild is still holding up. Did you use a aftermarket kit? If so what brand and what did you do if anything to the kit.
 
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