Newly obtained Stihl MS310 wont start, -How to diagnose the problem???

[Razorhunter]

My brother just gave me a Stihl MS310 that won't start. Saw appears to be in really good condition, and I'm fairly certain was well maintained, but it won't start and I need help from those more knowledgeable than me.  I'm very mechanically inclined, and I know these engines need fuel, spark and compression to run. However, I'm no expert, and could use tips on what steps to take to diagnose the problem. So far, I have been told to do the following:

-attempt to crank saw, then pull plug to make sure plugs tip is wet with fuel. I suppose this will confirm that carb us doing its job and pumping fuel to the cylinder?

-check plug itself obviously (afaik, plug should be light brownish in color?) Also check for spark by pulling rope while plug is touching metal object to check for spark.

-remove muffler/or muffler cover? at front of saw, and check to see if spark arresting screen is clean? Also look behind muffler at piston itself to see if its all scored up or damaged in any way? I'm a bit confused here, as I thought the piston had a ring around it, which is really the only part that touches the cylinder walls, so I'm unsure how the piston could/would ever be scored all up??? However, I was indeed told to check for a scored piston however. 

-locate and check.fuel line(s) for cracks/damage


Questions:

1. What other steps should I take to diagnose problem?

2. Manual is unclear: Does chain brake have to be engaged to start saw?

3. I've seen others talk about this very same model saw, and theyntioned turning both the low and high carb needle screws out by 1 full trn or more. However, my needles don't even have that much adjustment in them. I will double check this, but I think onethe High needle only has 3/4 of a turn of total adjustment, and I forget what the L has. Either way, I remember I couldn't even unscrew either needle as many turns as was recommended to me by one thread post I read here!


If anyone could offer steps I should take to diagnose this saws problem, I would greatly appreciate it guys. I'm almost certain its something minor, but I just need help finding the problem. Thanks for any help you guys can give.

[clww]

Well, two things I can add are: The chain-brake does not have to be engaged to start, but I would highly recommend it. How long was the saw sitting since the last time operated? I'm questioning the gas mix. It will get "old" if the saw has been sitting around, especially the "magic" ethanol.

[Razorhunter]

No idea how long it sat,  brother hinted that it could've been a while, but not sure. I'm kind of on my own getting it figured out. Btw, on a similar note, should I use ethanol free gas in my chainsaws? Is there any reason to do so?

[clww]

I'd recommend avoiding ethanol in any saw, or any other small engine.
In a little bit, there will be some much smarter members on here to help out with your saw problems. Just be patient.

[beenthere]

So, did you start off with fresh fuel mix? or try to start with old fuel still in the tank?

Did you have spark when checking for spark?

Then, did you add some fuel to the cylinder and put the plug back in and try to get some semblence of running?

Fill us in up to this point.

[Ianab]

The scored piston is a sign of serious internal injuries. InN normal use, yes the piston ring is what contacts the cylinder wall, and slides up and down on a film of oil. There is very little wear as there is actually no metal-metal contact.

BUT, if "someone" forgets to put oil in the fuel mix then things go bad pretty quickly. Thing overheat, the ring(s) loose tension, the piston rubs metal to metal on the cylinder, and starts to melt... Running the saw lean, either from a faulty carb or incorrect settings will have a similar result. (Excess heat + less oil = dead engine)

First check is that the saw has compression. You can get a compression gauge for this, or a rough and ready check is to hold the starter cord and let go the saw. If it unwinds all the way and the saw is sitting on the floor, it has no compression, and isn't going to start. If it comes out ~12" and comes up against the cylinder compression, that's a good sign.  Talking the muffler off and looking at the piston is another good check. If that's all scratched or melted, then look no further, it's not going to go without major surgery.

Then you check for a good spark. Sometimes it's worth just putting in a new spark plug even if it looks OK. They behave differently in a compressed fuel mix compared to open air.

Then that leaves fuel, namely the carb and fuel lines. One trick is to squirt a few drops of gas into the carb, and try and start it. If you have compression and spark it should at least "pop". If it does, you know it's a fuel delivery issue. If the saw has been sitting for a while with stale gas, especially with ethanol in it, all sorts of funky things may have happened inside the carburettor. Most likely is some of the rubber components have hardened and aren't working properly. A "carb kit" replaces all these perishable parts, and usually gets things working again.

Anyway, that's some ideas to work on.

Good luck

Ian

[Razorhunter]

Ian, (and others), THANKS SO MUCH for your help thus far. I'm headed home to start the diagnosis and will be posting sporadic updates as I progress.
  I just stopped by my local Stihl dealer. Grabbed a new plug, fuel line, some oil and carb rebuild kit. They seem very honest and weren't trying to profit off me at all. While their real mechanic was busy out back, the guys at the counter are still somewhat knowledgeable and offered this advice:
  First off, a new carb is $91.40, so I bought the rebuild kit for only $10.95. However, the guys told me that my plan to clean the carb via soaking in carb cleaner before rebuilding it, might not work. Apparently they are saying it must be cleaned via an ultrasonic cleaner, which is what they do. I've personally never heard of a carb that couldn't be cleaned via soaking in carb cleaner...???
  Anyhow, I've taken muffler off and piston looks absolutely great. No visible damage or carbon buildup to speak of. Compression seems good.
  Headed home now with new fuel delivery line, new fuel filter, carb rebuild kit, and fresh ethanol free fuel from the only store in town that still offers ethanol free fuel.
  Like I said, will post updates as.soon as I have them.


Oh, one other thing. My bro hinted spark plug boot may need replacing. Why he said that is beyond me, but I went ahead and bought a new boot. My question is "HOW does new rubber boot attach to existing plug wire??

Also, can anyone advise on where to start with needle settings? Another MS310 thread stated 1 or 1.5 full turns out with regards to one of the needles, but the crazy thing is that my 2005 model saw won't even allow more than something like 3/4 of a turn. This is the MOST the High needle even has for adjustment. Forgot how much the Low needle has, but you guys get the point here. Thanks for all your great help guys!

[JohnG28]

There are caps on the H and L adjustment needles that restrict them from moving more than a certain amount. You should be able to turn the H all the way out (counterclockwise) and the L about 1 and get it running from there once everything is in good order. As for the spark plug boot, see if it has any spark you can see first and go from there. If it does give a shot of mix fuel through the plug hole and give a try.

[Razorhunter]

Ok quick update guys. I installed new fuel filter/clunk, fuel pickup line, and spark plug. Also new fresh non-ethanol fuel mix.

Compression: as stated previously, piston looks great with absolutely zero scratches, flaws etc, when viewed through muffler port. I did the pull rope hang test and saw doesn't fall to ground too easily, but with full tank of fuel, it doesn't exactly hang at first compression of cylinder. It barely wants to fall down to the ground, so I'm hoping this is enough compression?? Like I said, this is with a full tank of fuel and chain oil, and it almost wants to stay there, hanging in mid air, but it just won't do it. It does fall slowly to the round.

Spark: Here's the thing. I don't seem to be getting any spark at all. I pulled plug and then reattached boot to plug. In my almost pitch dark basement, I can't see any visible spark, while pulling start rope, and holding plug up to metal object. Unless I'm doing something seriously wrong, I am not getting any spark here. I've done this same test with motorcycles over the years, and always could see visible spark, so I think I'm prforming spark test correctly. Spark plug boot APPEARS ok, but I do recall my brother saying that a new plug boot/wire might be needed. I do not know how a new plug boot installs over the end of the plug wire however, so maybe you guys can tell me? Heck, what else could be preventing me from getting spark anyhow???

Btw. I also dabbled fuel down on plug hole, tried to crank, and nothing. No spark is obviously the main problem I'm having here.
Thanks for the continued help guys. More to come.

[Ianab]

Because of all the plastic on a MS310, where are you grounding it? The bar etc are mounted on plastic, so they wont make a circuit to give a spark. It needs to be touching the fins of the cylinder to make sure you have a good circuit. On a motorbike the metal frame and engine are both "earth", so it's easier to test. May not be the same with a 50% plastic saw.

Ian

[Jim_Rogers]

It could be your coil.
There should be a metal strip on the side of the flywheel that spins around on one end of the crank shaft. If that metal strip got rusty it may not make a spark.
You could check to see if it's rusty, and clean it with some emery paper.
I think the gap has to be set just right as well. That is the gap between the flywheel and coil.
Or check your wires to your coil and see if one is broken.
Just some ideas to look at.
Good luck.

Jim Rogers

[92497pmu]

bump
Razorhunter- we have very similar problem with a MS361 PRO
What were your final results?

[sablatnic]

Before dismantling everything, pull the stop wire from the ignition coil, and check the ignition again. That way you have eliminated everything but the coil and high tnsion wire.
Good luck!