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I have a MS 460 that will not start. It was not producing spark. Now it does intermittently with a different coil. The second coil is from another 460 that was running but cylinder went bad. Will not even try to start with carb cleaner. Done leakdown test also and had a small leak at the decompression valve. Cleaned and tightened it. It was after all of this when I noticed the intermittent spark. Before then I was getting a good blue spark. Tested with a spark tester.

intermittent spark usuall means the coil
is bad try disconnecting the ground wire from the coil and check for spark again if it's better you have ground sometimes shorting in the wires leading to the kill switch

Will do. Let you know tomorrow what I find thanks.

Remove the wire to the coil and try checking for spark again. I had a honda lawnmower in my shop where the coil was completely dead and the diagnosis was to remove the wire to the coil to see if there was spark. If no spark then replace coil. You already replaced the coil but that doesn't mean the replacement is good. If after removing the coil grounding wire the spark does not improve I would try a known good coil. Maybe ask the nice fellows at the stihl shop if they have a test coil for a 460 they would let you try.

The fact that you replaced the coil with another one and now you at least have intermittent tells you that either the coil grounding wire is intermittently grounding out or you have a weak coil. Trace that grounding wire to make sure it hasn't rubbed through to ground. Also, make sure the multi-function lever where the wire goes to is working properly.

Got beat out again, this time by Briggs92

That helped the spark. I haven't looked for the spot on the ground shorting out yet but I wanted to try getting it to fire. Still no go. Out of all the things I have worked on I have never had problems getting one to fire with carb cleaner. I have good compression, I have good spark now, and I add the fuel to the formula. I have pressed the decompression valve and tried it without pressing it. For some reason I can NOT get this thing to fire with fuel or carb cleaner. Please help!!!

I'm sure you already know this but an engine needs the right amount of air, the right amount of fuel, compression and spark at the right time to operate properly. If one of the above factors are missing or in the wrong proportion the engine will not run or may run poorly.

Is the spark plug wet with fuel? If not, I'd put a small amount of two stroke mix directly in the cylinder through the spark plug hole and try starting it. Make sure the choke is wide open. If the engine "burps" then you are on to something. Double check that plug and tell us the condition of it - wet or dry?

That's what I have been doing. I have put it in the spark plug hole and the carb venturi. Neither one does anything. Of course after doing that the plug is wet. I also used compressed air and dried the cylinder out to make sure it wasn't too rich in there and tried again. Brand new plug too.

If everything was correct the engine would have at least "burped" to show some sign of life. However since this didn't happen it's leading me to believe the coil is weak. What kind of spark checker did you use? You can easily make your own spark checker from a known good spark plug by clipping the side electrode off at the base where it connects to the rest of the plug. By doing this you will force the coil to produce the maximum amount of energy to jump the much larger gap instead of the usual .025-.030 of a regular spark plug. Try that and see what happens. Make sure the metal body of the tester plug is grounded and the spark should jump to the side of the tester plug. If the coil cannot make the spark jump the larger gap, the coil is suspect.

Did you ever go the the local Stihl shop and ask the kind folks there if you could borrow a test coil?

You mentioned that when you put some fuel in the cylinder through the spark plug hole the plug gets wet from fuel-this is what leads me to believe the coil cannot produce sufficient enough spark under compression to start the engine.

I used a regular spark tester from a parts store. I had the gap between .30-.40. It was a food blue spark. I also check the plug by grounding it to the cylinder. Same result. I have not made it by the Stihl shop yet.
If it was not producing a good spark under compression would it not produce a good spark with the decompression valve pressed. I don't have much experience with the decompression valves.
This saw was purchased from a pawn shop and has not run since purchased. So I don't know any history on it. It just has me going nuts. Haha!!

I've got an MS250 that I just put a new flywheel on due to the perment key breaking.Have you checked that ?I then had a hole in the fuel line and had to tear the whole thing apart just to replace that $14.00 line.Any more problems and I might have to try a diff. brand of saw...russ

I have not checked the flywheel key. I thought about that while I was typing that last post.

Wouldn't have this problem if it was a Husqvarna!! Haha

Have tried to close the gap on the coil? .008 instead of .010.

I have always just used a business card. I will check that too. I am at the fire station today so it will be tomorrow before I can check.

I know that the vast majority of people use a business card, but I have found that they are unreliable. One year I had my students each bring in 10 cards and mic them. Card sizes ranged from .006-.013. Only 40% actual measured .010. The most accurate substitute for a feeler gage that I have found is a microfiche card folded in half.

I tried a good coil and adjusted the gap to .010 and also .008. Still nothing.
I also checked the key and everything is in place as it should be.

bwestbrook said:

I used a regular spark tester from a parts store. I had the gap between .30-.40. It was a food blue spark. I also check the plug by grounding it to the cylinder. Same result. I have not made it by the Stihl shop yet.
If it was not producing a good spark under compression would it not produce a good spark with the decompression valve pressed. I don't have much experience with the decompression valves.
This saw was purchased from a pawn shop and has not run since purchased. So I don't know any history on it. It just has me going nuts. Haha!!

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Just wondering if you did a compression test on it? Even if it was in the fault of the decompression unit, still you'd have to get enough compression to run. With good blue spark and compression it should run! Seems plenty of gas is not the issue here. I just use a tiny amount of 2 cycle gas mix, say 1/4 teaspoon down in the spark plug hole and pull it over. It should at least give a quick start and run till the gas is burnt out. I hate a temperamental unit! Good Luck

I got 90 psi on compression test.

There is your problem. Remove the muffler and look at the piston it will be scored from a lean mixture. I have rebuilt a bunch because they try to start them with old gas with E-10 in it and the fuel has seperated(phase seperation) I use the aftermarket pistons and cylinders from here

Bailey's - NWP Cylinder Assembly for Stihl 046, MS 460 Chainsaws

If you look around you can find a 54MM big bore kit which is what i use.

Rob
Ann Arbor Firefighter, Michigan
local 693

Gentlemen: This is a great forum. This afternoon, my MS460 refused to start although it was running okay last week when I shut it down. After many crankings, I tried some ether. When that did not fire, I put a screwdriver into the spark plug boot and pulled the rope vigorously, several times, with no detected electrical charge. From what you all have written, my coil must be bad. Or, is there something else to look at? Can the throttle/choke switch get out of sync somehow?. As an amateur, should I try replacing the coil myself?

MrWobbly said:

Gentlemen: This is a great forum. This afternoon, my MS460 refused to start although it was running okay last week when I shut it down. After many crankings, I tried some ether. When that did not fire, I put a screwdriver into the spark plug boot and pulled the rope vigorously, several times, with no detected electrical charge. From what you all have written, my coil must be bad. Or, is there something else to look at? Can the throttle/choke switch get out of sync somehow?. As an amateur, should I try replacing the coil myself?

Click to expand...

Did you remove the spark plug and ground it out rather than a screwdriver?

Also make a new post of your problem and you will get a better response.