Another Stihl MS 310 issue...

This saw came in and I was told it quit running after using it for a few hours.  Okay, no big deal I thought, i'll check the basics and go from there.  I pulled the plug, didn't look too bad, hooked up an in line spark tester and had good spark.  Tried cranking it over a few times and got nothing.  Put a teaspoon or so of fresh mix into the sparkplug hole, re-installed the plug, and tried again.  Nothing.  Hmm.  I guess this saw is gonna make me work for it. I pulled the carb off and inspected all the fuel lines and tank vent line, seemed good.  Took the plug back out and shined a flashlight into the intake port while slowly pulling on the starter rope.  I could see the piston moving and could see the cylinder and piston was soaked in fuel, and each time i pulled the rope I could see drops of mix spitting out the crankcase vent line.  Okay, it's flooded.  I pulled the carb apart thinking the needle valve was stuck open, letting fuel pour into the motor.  Nope, looked fine, and the metering lever was still at the correct height.  I took the fuel pump side of the carb off, and came across this mess.

It appears these Walbro HD series carbs have two very small holes on the underside of the fuel pump diaphragm end of the carb, which I'm assuming act as an atmospheric vent.  You can see them on the bottom part of the photo at the 3 and 6 o'clock position.  These were pretty well plugged up, and I'm assuming that the sawdust gunk you can see made it's way through those holes over time, building up enough to impede the vents and not allow the fuel pump diaphragm to function properly, hence the flooding issue.  Now it was only a matter of spraying this out and cleaning it up good with carb cleaner, and re-assemble.  I've usually had bad luck not damaging the diaphragms and gaskets when tearing down carbs like these, they usually are pretty stubborn about coming apart cleanly, but this particular carb was cooperative, no need to replace them.  After I got everything put back together the saw fired up and ran beautifully.  It's funny, you would think a carb so gunked up like that would cause no fuel to be getting to the motor, not the opposite problem of flooding.  If it's plugged up in the right place though, it will indeed flood the motor.  One thing that sort of threw me off was the fact that the plug was dry and looked good when I pulled it, but I'm contributing that to the fact that I let the saw sit just long enough for the plug to dry off while I took a lunch break.  Oops.

Stihl MS310 oiler problem

This particular saw, a Stihl MS310, was having someone oiling issues, as no oil was reaching the bar.  I'm hoping this post will help any other Stihl saw owners if they encounter the same problem, which from what I understand isn't all that uncommon.  Ok, this is how the oiler works, the oil tank has a rubber line with filter on the end inside it, not much different to the fuel tank feed lines on many two strokes  This line and filter is where the oil pump pulls the oil from the tank through.  The line exists the interior of the tank at an angle towards the rear and bottom of the saw and across towards the clutch and bar side.  If you remove the handle of the saw itself you will see it exit the main case and tank on the saw, do a 90 degree angle back up towards the clutch side of the saw, and re-enter the case.  To access the oil pump you need to remove the clutch, take off bar nuts, cover, and remove the bar and chain.  Remove the E clip, washer, and sprocket on top of the clutch drum..  The nut on the clutch is 19mm and left hand thread.  To keep the clutch from spinning while you remove it, simply remove the spark plug and feed a few feet of small diameter nylon rope through the spark plug hole so when you spin the motor over the rope stops the piston.  Now you can remove the clutch nut, remember its left handed so you need to turn it clockwise to loosen.  Once the clutch is loose you can remove the roller bearing on the crankshaft, as well as the large washer, and expose the oiler drive gear.  Examine the drive gear, if the wire arm of it has a worm end it won't engage the groove on the clutch drum, which then won't spin it, which in turn won't drive the oil pump .  You will most likely see a lot of old dirty saw dust and gunk, so lightly blow it clean with compressed air, being careful not to blow any dirt into the spark plug hole.  There will be two no. 27 torx head screws that hold the oil pump on, and you will see the black oil feed line  we discussed early attached to the lower nipple on the pump.  The upper outlet to the pump is attached to a white plastic elbow which continues to lead to the passage in the main chainsaw case, and the oiler hole which emits the oil to the chain.  You can disconnect the black rubber hose from the inlet of the pump and blow compressed air through it, which should eventually spray back out to the filter in the tank, so empty your tank first as to avoid a mess of oil being sprayed everwhere.  You can remove the oil pump all together from the saw, and make sure the worm drive screw moves freely, and blow it out again with compressed air.  If their is a lot of gunk I recommend wd-40 to help loosen it up.  Now you can again blow compressed air through the outlet hole where the oil reaches the bar to make sure its clear of  obstructions.  With everything clean and clear, you can reinstall the oil pump attach the rubber inlet hose. I use a dab of blue loctite on the screws securing the oil pump.  While reinstalling the clutch drum, you must make sure the arm of the oiler gear wire engages the slot on the clutch drum, or the oil gear will not spin and drive the pump  I used a long breaker bar with 19mm socket to torque the nut back down. Don't use an impact gun to remove or install this nut or you could possibly shear the keyway on the flywheel  With all that said re-install the bar, chain, and cover.  Fire up the saw and see how shes oiling.  Many of the MS series saws have a screw underneath the saw labeled with a "chain link" icon and "oil drop" icon.  This is the oiler adjustment screw.  Using a long flat tip screwdriver can adjust the amount of oil the bar gets, clockwise increases it, counter decreases it. This particular saw was leaking lots of oil near the muffler area.  There is a plastic plug inserted by the factory near the oil outlet hole galley that can come loose and fall out.  To remedy this you will need a course thread 1/4" tap, along wit a small allen head set screw of the same thread type.  Tap the threads in the hole, smear a bit of RTV silicone on the threads of the set screw and insert until snug.  No more leaks and the oil can now reach the bar adequately.  Hooray!  Pat yourself on the back for fixing your own saw and not having to take it to shop and pay 90 dollars an hour in labor!