MS 310 Bogging, Not Full Power

ms310 · October 30, 2015, 05:05:45 PM

Issues with the old Stihl MS310. I'm not getting full power and bogging when trying to cut. Almost like it isn't enough getting fuel? Saw has problems even cutting cause it just doesnt have the rpms like it did a year ago... Just binds up. Sometimes I have to feather the trigger or it will kill. Starts and idols like a champ though.

Let me start by admitting that fuel sat in the tank last winter. So, here is what Ive done so far. I have cleaned muffler screen, cleaned and checked gap of spark plug, Replaced fuel filter and fuel line, mixed up fresh fuel, and air filter is clean too. I'm thinking next a carb kit??

Any advice? This is frustrating...

deerslayer · October 31, 2015, 12:20:05 AM

Assuming your piston looks good (not scored), you probably have crud in your carb. If you can open it up and clean it out it may solve the problem. Especially check the little screen in the carb as that tends to get crudded up.

PASS_AUF · October 31, 2015, 04:31:17 AM

If you have access to a compression gauge it's always worth pulling the compression just to see where you're at. It wouldn't surprise me at all if your issue is fuel related, especially if it had ethanol blended fuel in it all winter. If it's really nasty inside you may consider taking it to a shop with an ultrasonic cleaner, the internal circuits can be tricky to get clean.

ms310 · October 31, 2015, 12:21:54 PM

Yeah. Iagree with you both. I believe it is fuel related, carb related. Off to get a carb kit today. We'll see...

Magicman · November 01, 2015, 02:54:40 PM

Welcome to the Forestry Forum, ms310.

Ada Shaker · November 01, 2015, 09:54:40 PM

Guys, Don't forget to check your exhaust if your motor just idles and doesn't rev up because it cant expel/breath. We have wasps here that like to build mud nests in nooks'n'crannies like exhausts/mufflers. Always worth a look IMHO B4 spending too much time & cash on carby'pull'aparts. Air/Ignition/Fuel, both Inlet & Exhaust for air flow. Good luck.

ms310 · November 02, 2015, 07:24:02 PM

No carb kit. The one place didnt have it... Didnt have Zama kits and mentioned they are not meant to be rebuilt and he said I should just buy a new carb. Not going with his advice at this point.

Pulled off the carb today and top and bottom plates of it. All looked good. Nothing real dirty or gunky. Had some saw dust on air in-take diaphram, but nothing to crazy. Little screen looked fine. Pulled it out and looked through it towards the sun. Took off the little screw with jet needle and spring, all looked fine. So, fired up the saw and still acting the same. Full throttle gives weak rpms and oscillates while I'm moving it around in different positions.

Mmmm, what to do now?? Can the carb be still the problem even though it all looked fine? Can it be a problem within the carb internals?? Should I just go with a new carb??

my frustration is building....

Kingmt · November 02, 2015, 07:33:48 PM

Since all the fuel from last year is out of it now I'd suggest making sure the manifold is nice & tight. I was have the same problems with one of my saws & thought I knew what tight enough on the clamp was. I decided to tighten it more anyhow & it seems to have fixed the problem. Seemed way over tight for the little clamp but I guess I didn't realize just how many mercrons this little thing pulls.

Texas-Jim · November 02, 2015, 08:33:36 PM

What do you mean by oscilates? If you mean the engine speed alters i would be looking for an air leak, it may not be carb.

And for your info a brand new carb is $42.16
1127 120 0605 Carburetor HD-21D.

ms310 · November 03, 2015, 10:50:29 AM

Not sure if oscillating is the correct word. When the powerhead is moved around with full throttle the rpms become varied. Kinda goes in and out. I'm still thinking about the fuel issues and posssible air coming from somewhere.

Kingmt, where would I snug down the manifold bolts? Under the top cover? I was also thinking the intake boot could be faulty?

ms310 · November 03, 2015, 04:00:43 PM

My local Stihl dealer quote me $95 for new carb. Whew......... Not in stock either...
So, I'll be ordering one from ebay today.

deerslayer · November 03, 2015, 07:43:03 PM

a crack in a fuel or impulse line can cause these symptoms too. I have never seen a bad impulse hose on this series saw but have encountered bad fuel lines.

joe_indi · November 03, 2015, 10:40:06 PM

These are other possibilities
#1.
Since you say it was stored with fuel, chances are that the jet valve diaphragm is sticking.It is supposed to open/close at every stroke of the piston. If stickiness slows it down air could flow back into the metering chamber causing a fuel lean out by reducing fuel volume in the metering chamber. You get air and fuel in the chamber. Tilt the saw to the position of a horizontal cut or bar vertically down and air instead of fuel comes through the jet valve causing a 'running out of fuel' feeling. Tilt the saw starter side down or bar vertically up and the saw will get more fuel causing a 'its starting to flood' feeling.

#2.
The oil seals could be weak, they would be fine at idle or low mid range. But extra vacuum at acceleration at WTO would cause the seals to open up causing a lean mixture from the extra air.

#3.
The air filter is blocked which causes the compensator to prevent the metering diaphragm from moving down to open the metering valve. This will cause lean outs at WTO.

Joe

Ada Shaker · November 04, 2015, 03:54:19 AM

Sorry, miss-read your post earlier.
You did clean the spark arrestor.
When cleaning out the carby I usually pull it completely apart and stick it in a small jar and submerge it all in carby cleaner for a week or two. Particularly the main carby body. You'd be surprised how much varnish and the like ends up coming out of those jets that are generally inaccessible from a basic general clean. The cleaner generally ends up finishing the colour of tea. Then low pressure blow the jets and the like with a little compressed air (mindful of the inlet filter and the like). I generally give it a light blow a few times and then re-submerge back into the fluid, during the soaking process. The end result is usually a squeaky clean carby that I'm pretty confident has no blockages anywhere, and a jar with fairly dirty carb cleaner.

Kingmt · November 04, 2015, 08:21:20 AM

Quote from: Ada Shaker on November 04, 2015, 03:54:19 AM
When cleaning out the carby I usually pull it completely apart and stick it in a small jar and submerge it all in carby cleaner for a week or two.

Is suggest sticking with gasoline. Gasoline will dissolve varnish. Especially that with ethanol in it. Just ensure the washing container is sealed while it is soaking. A little shake once in a while goes a long way to help. If you can set it on to it the clothes washer while a load washes even better.

Gasoline will be less likely to damage anything.

Kingmt · November 04, 2015, 08:25:41 AM

Quote from: ms310 on November 03, 2015, 10:50:29 AM
Not sure if oscillating is the correct word. When the powerhead is moved around with full throttle the rpms become varied. Kinda goes in and out. I'm still thinking about the fuel issues and posssible air coming from somewhere.

Kingmt, where would I snug down the manifold bolts? Under the top cover? I was also thinking the intake boot could be faulty?

The chamber between the carb & block is called a manifold. That is where the fuel mist is mixed with air to make the vapor. I only needed to tighten the hose clamp around the carb.

ms310 · November 17, 2015, 07:24:09 PM

Well. installed the new carb. Adjusted the LA, H, L to what the other carb was at. Just by counting turns on the old carb. Figured it had to be close. Now it is hard to start, idles poorly, if at all. I cannot determine if I fixed the problem because it is just running like crap now. Urghhhhhhhhhhhhhhhhhhhhh. What a pain...

Without a tach, i dont want to just start turning adjustment screws.... Is it worth trying to follow the owners manual about carb adjustment? It seems very basic?

leeroyjd · November 18, 2015, 04:15:13 AM

Maybe try rinsing out your fuel tank and replacing the fuel filter a second time.
I had a 460 running erratic and after doing the basics I did this and it was fine.

deerslayer · November 18, 2015, 04:35:06 AM

Assume the new carb didn't come with limiters. Turn the H screw all the way in and then turn it out 1 1/4 turns. Turn the L screw all the way in and then back it out 1 full turn. Start with that and see how it runs. The carb will need to be tuned to the saw. Don't assume the old carb setting will transfer over to the new one.

deerslayer · November 18, 2015, 04:38:15 AM

I see you installed a new fuel line. Was it an OEM line or aftermarket? I ask because I've only had about 50% of the aftermarket lines work. If tuning the carb doesn't solve the problem, reinstall the OEM line and see if that helps.
The aftermarket lines are slightly thicker and will pinch off the fuel where the line bends.

CR888 · November 18, 2015, 04:53:05 AM

My guess is crank seals from the op clue as to how it behaves when turned sideways, but it could be one of a number of thing's. Can you do a pressure/vac test?

ms310 · December 27, 2015, 05:30:03 PM

UPdate... Seeing its about the new year, I just got my 310 back from the saw shop on Monday. Saw ran fine for half a tank of gas and now idling fine but continues to bog under any type of throttle. Saw is worthless beside sitting and idling. Im even running the Stihl premix fuel in it. I have not done a pressure/vac test. Sounds like another expensive shop visit. Im out of $$ and patience. Saw is going on Craigslist.

Thanks for everyones help

beenthere · December 27, 2015, 06:17:52 PM

That is a bummer. What did they do for it at the shop?

ms310 · December 28, 2015, 01:45:36 PM

They tuned the new carb I installed. RRan fine wehn the tech brought it out and started it. But after about 1 tank through it started to do it again... bogging, no power. Seems Im back where I began. Nothing solved.