Hello this is my first post. My MS 310 has a wiring issue that I can’t fix. I have tried to find a schematic detailing the simple wire harness with little luck. Any chance one of you could explain the wiring layout. The wire going to the ground point on the coil broke off so I ran another wire from it to the metal dogs up front. I would like to trace the wire but I believe I would need to dismantle the entire saw ? Any suggestions would be appreciated.
MS 310 Coil Wiring Help ?
- Thread starter jpsbgt
- Start date
Photos will help- but the ground is a T27 screw located on the flywheel side of the cylinder- just to the front of and slightly above the coil- should be a wire with a ring terminal from the coil and another going away to the metal section of the master control switch.
Well you have to pull the recoil starter off and enough of the saw to expose the flywheel- but should be plain to see after that.
The cover is off ! No visible sign of ground wire. Just the two yellow wires going into a plastic access area. You can not see the area on cylinder where the wire terminates inside. I have spark but saw will not run. I shot a bit of starting fluid but nothing ?
If you have to resort to starter fluid- you have bigger issues.
Okay- Stihl plastic case consumer grade saws are all pretty much the same- one wire with a ring terminal runs alongside the sparkplug wire and has a spade female terminal that goes onto the flat bit of spring steel that acts as the kill switch on the master control- also a black wire- spade female at coil end, copper tube at other- this is what the spring flat steel contacts at the master control switch to ground the coil.
There should be a short jumper wire with two ring terminals that go at coil mounting bolt to a bolt on the cylinder so the coil can be grounded- as otherwise it is mounted to insulated plastic and the stop/kill switch will never work.
Okay- Stihl plastic case consumer grade saws are all pretty much the same- one wire with a ring terminal runs alongside the sparkplug wire and has a spade female terminal that goes onto the flat bit of spring steel that acts as the kill switch on the master control- also a black wire- spade female at coil end, copper tube at other- this is what the spring flat steel contacts at the master control switch to ground the coil.
There should be a short jumper wire with two ring terminals that go at coil mounting bolt to a bolt on the cylinder so the coil can be grounded- as otherwise it is mounted to insulated plastic and the stop/kill switch will never work.
I have always been told that if you have spark , fuel and compression the engine should run. I tried the starting fluid just to eliminate lack of fuel as a reason it won’t run. I am assuming that the one yellow wire going to the cylinder ground point has come off or broke off from vibration. I confirmed spark by holding the plug against the cylinder head, strong spark. Engine has great compression ! Very confusing ! Bob I see no short jumper wire you mentioned ? I will open up the cover again and take a photo. Really appreciate your time and patience.
Spark, fuel and compression is a general minimum and assumes a few things.
You also need correct timing of that spark and the correct air/fuel mixture reaching the combustion chamber.
So a shorn key on the flywheel, or substantial air leak can stop a saw from firing.
Compression- unless measured with a true small engine gauge- is subjective also.
As a rule, I am not fond of the big Stihl plastic saws- have lots of non repairable wrecks here to prove it- but with any saw, it comes down to the same basics and a pressure and vacuum test will eliminate a LOT of guessing and parts chucking.
You also need correct timing of that spark and the correct air/fuel mixture reaching the combustion chamber.
So a shorn key on the flywheel, or substantial air leak can stop a saw from firing.
Compression- unless measured with a true small engine gauge- is subjective also.
As a rule, I am not fond of the big Stihl plastic saws- have lots of non repairable wrecks here to prove it- but with any saw, it comes down to the same basics and a pressure and vacuum test will eliminate a LOT of guessing and parts chucking.
Well stated Bob ! Saw operated perfect last November. Went to start it in April and nothing. Borrowed a friend’s to clean up from a windstorm and just now getting back to figuring out the issue. I always run the saw out of gas before I put it away. Fresh non-ethanol with Royal Purple two stroke oil. New air filter. Going out to take a photo of the coil and wiring.
Bob I have determined that you need to pull off the flywheel to inspect the ground wire on the cylinder, I believe I can see it but not certain that the wire is connected properly with no short or broken. I can’t do it until tomorrow.
Following up ! I installed a new Stihl coil and spark plug. Grounded the plug and found strong spark. Reinstalled it in cylinder. Put a small amount of gas into the intake and no start, not even a misfire ! I am officially stumped !
So we are still parts chucking?
Obviously something is still astray- something needed for combustion.
If you do not have the tooling required and cannot cobble something up for a pressure and vacuum test- I would be taking the saw to a Stihl shop and asking them to do one on it- confirm all is correct there first off.
Yes they will charge you to do it- but you are already spending money on parts you may or may not have needed.
One simple Bubba test you can do is remove the spark plug, tip around a teaspoon full of oil- any oil, mix oil, bar oil, engine oil- into the spark plug hole on top of the piston. Swill it around a bit, pull the starter a couple of times-plug back in, dribble of fuel in the intake and try to start the saw.
The added oil will run a film down the cylinder walls to temporarily up compression- if it fires up it will smoke like a biarch- but will prove the theory.
Obviously something is still astray- something needed for combustion.
If you do not have the tooling required and cannot cobble something up for a pressure and vacuum test- I would be taking the saw to a Stihl shop and asking them to do one on it- confirm all is correct there first off.
Yes they will charge you to do it- but you are already spending money on parts you may or may not have needed.
One simple Bubba test you can do is remove the spark plug, tip around a teaspoon full of oil- any oil, mix oil, bar oil, engine oil- into the spark plug hole on top of the piston. Swill it around a bit, pull the starter a couple of times-plug back in, dribble of fuel in the intake and try to start the saw.
The added oil will run a film down the cylinder walls to temporarily up compression- if it fires up it will smoke like a biarch- but will prove the theory.
Parts chucking ? I replaced the coil because it’s the original and over twenty years old. The plug is an easy thing to check. I appreciate your input. The compression is fine , piston and cylinder have zero signs of scoring, nor scratches. I have been very diligent about fuel and quality of oil. Bob I have done all the normal steps to diagnose the no spark issue. I had a new coil so why not try it to eliminate it. Again the unit has great spark out of the cylinder. I have not spent any $ so far. Labor and frustration yes. Taking it tomorrow to a Stihl shop.
20 years is nothing for a coil= I will have saws here from the 1960's still running on original coils.
The wiring you describe first post is Mickey Mouse and for me, it is not proved the old coil is bad- possibly the HT lead or plug cap might be- but nothing thus far suggested the coil needed replaced and just coz ya say something is good- is not proof it is good.
Get where I am coming from now? Compression is fine- is an opinion- video of a test being done to confirm with an appropriate gauge and I will believe it as proof.
I cannot see the saw bar one low detail photo- so I go through what might be obvious wrong and how to go about testing it to eliminate that suspect with proof.
The wiring you describe first post is Mickey Mouse and for me, it is not proved the old coil is bad- possibly the HT lead or plug cap might be- but nothing thus far suggested the coil needed replaced and just coz ya say something is good- is not proof it is good.
Get where I am coming from now? Compression is fine- is an opinion- video of a test being done to confirm with an appropriate gauge and I will believe it as proof.
I cannot see the saw bar one low detail photo- so I go through what might be obvious wrong and how to go about testing it to eliminate that suspect with proof.