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FS85 no spark
#1
D
DogT1
D
DogT1
This thing has been a bear from the get-go. It ran fine sometimes and erratic sometimes, but recently it just quit. I guess it's about 15 years old. Pulled the plug and lay it against the engine, pull and no spark. So I buy a aftermarket coil from ebay. No spark. Got another from a different vendor with carb. Still no spark. WTF? What are the chances I get 2 bad AM coils? The original Stihl coil measures 1.7Megohms from the terminal to ground. The 2 aftermarket coils both measure about 380 ohms from the terminal to ground. I've even tried not even connecting the wires to the stop switch. No spark. Off switch works fine according to ohmmeter. Set the gap from 10 thou down to 6 thou and nothing. Magnet on the flywheel is strong, near as I can tell, it sure pulls the coil against it. Even tried 3 different plugs, the original, a replacement from the Stihl dealer and one that came with the carb/coil combo. Nothing. What's next, throw it out?
#2
S
shiftsuper175607
check for problem with the kill switch and wiring.
I had one the other day that shocked me when I touched it. It wouldn't start next time I went to use it.
I sprayed grime away from engine with cleaner and it is running great.
S
shiftsuper175607
This thing has been a bear from the get-go. It ran fine sometimes and erratic sometimes, but recently it just quit. I guess it's about 15 years old. Pulled the plug and lay it against the engine, pull and no spark. So I buy a aftermarket coil from ebay. No spark. Got another from a different vendor with carb. Still no spark. WTF? What are the chances I get 2 bad AM coils? The original Stihl coil measures 1.7Megohms from the terminal to ground. The 2 aftermarket coils both measure about 380 ohms from the terminal to ground. I've even tried not even connecting the wires to the stop switch. No spark. Off switch works fine according to ohmmeter. Set the gap from 10 thou down to 6 thou and nothing. Magnet on the flywheel is strong, near as I can tell, it sure pulls the coil against it. Even tried 3 different plugs, the original, a replacement from the Stihl dealer and one that came with the carb/coil combo. Nothing. What's next, throw it out?
check for problem with the kill switch and wiring.
I had one the other day that shocked me when I touched it. It wouldn't start next time I went to use it.
I sprayed grime away from engine with cleaner and it is running great.
#3
D
DogT1
D
DogT1
Duh!! On a lark, I put the plug in and squirted some starting fluid on the filter and it fired right up and ran if a bit high on the idle. It's always been erratic at idle. I guess just because I can't see the spark doesn't mean it's not there, and I was really looking for it. Makes me wonder if the first coil I got was OK. But I'm going to leave it as is. It's running.
Yeah, I'd checked the stop circuit for problems, one of the first things I did. It stops fine.
Yeah, I'd checked the stop circuit for problems, one of the first things I did. It stops fine.
#4
B
bertsmobile1
The spark you get from a magneto device is proportional to the speed that the magnets pass the coil and the strength of the magnets.
Over time magnets go weak and this is accelerated by heat.
A trimmer/ chainsaw runs anything from 7000 rpm to 15,000 rpm so a coil designed to run at those speeds will not produce a really strong spark at pull start speeds.
I & most other shops I know use a red spark tester to check for the existance of a spark and also have special clamps for holding engines so they are not bouncing all over the bench / floor which makes sparks impossible to see.
You might do well to get one for your tool box so the next time you don't end up buying stuff you don't need.
B
bertsmobile1
Duh!! On a lark, I put the plug in and squirted some starting fluid on the filter and it fired right up and ran if a bit high on the idle. It's always been erratic at idle. I guess just because I can't see the spark doesn't mean it's not there, and I was really looking for it. Makes me wonder if the first coil I got was OK. But I'm going to leave it as is. It's running.
Yeah, I'd checked the stop circuit for problems, one of the first things I did. It stops fine.
The spark you get from a magneto device is proportional to the speed that the magnets pass the coil and the strength of the magnets.
Over time magnets go weak and this is accelerated by heat.
A trimmer/ chainsaw runs anything from 7000 rpm to 15,000 rpm so a coil designed to run at those speeds will not produce a really strong spark at pull start speeds.
I & most other shops I know use a red spark tester to check for the existance of a spark and also have special clamps for holding engines so they are not bouncing all over the bench / floor which makes sparks impossible to see.
You might do well to get one for your tool box so the next time you don't end up buying stuff you don't need.
#5
D
DogT1
D
DogT1
I got a refund on the first coil, so that didn't cost me anything, I'm still not sure it works or not. I just can't remember if I even tried installing the plug with that coil. I'll try the new carb on it one of these days and see if it works any better than the original. Now I need to clean or get a new carb for my 036 chain saw. It's been getting rough to start, actually I can't start it any more, I have the yard guy use it. I just can't pull it fast enough any more and it's really exhausting to use with my bad back and all.
Good to know about the spark at starting speeds though. Everything else I've had, it's plenty easy to see the spark. I should have tried it in the dark. I did think about it, but never tried.
Good to know about the spark at starting speeds though. Everything else I've had, it's plenty easy to see the spark. I should have tried it in the dark. I did think about it, but never tried.
#6
T
The Specialist
You have established that you have spark. Where you have stated that you are having problems with it running, Change the fuel filter in the tank. You will need part number 0000 350 3502. The fuel filter is designed to capture water before it goes to the carb. With a piece of wire, pull it out of the tank, and remove it. Try and blow into it. You should have no resistance at all. Put the new fuel filter on it. Then start your trimmer. It may take some "feathering" of the throttle to get it going, as you have to remove the air out of the new filter. In the carb, there is also a 10 micron screen. These also get blocked with a sludge from the fuel. Remove the carb and where you adjust your idle speed, that big plate will have one screw in the middle. Remove that big screw and the whole plate will come off. Ensure that you do not damage the gasket, so just remove it slowly. On the carb block, you will see the screen, Hook it out with a needs. In a little bit of gas, put the screen in it and with your thumb nail, rub the screen. Blow it out. Hold it to the light and you should see that it is clear. With and unsharpened HB pencil. Put the screen back in its position and push down on it with the pencil. I find that the pencil works the best and it is the perfect size. Put the carb back on and I am sure that your machine will work much better than new!!
T
The Specialist
check for problem with the kill switch and wiring.
I had one the other day that shocked me when I touched it. It wouldn't start next time I went to use it.
I sprayed grime away from engine with cleaner and it is running great.
You have established that you have spark. Where you have stated that you are having problems with it running, Change the fuel filter in the tank. You will need part number 0000 350 3502. The fuel filter is designed to capture water before it goes to the carb. With a piece of wire, pull it out of the tank, and remove it. Try and blow into it. You should have no resistance at all. Put the new fuel filter on it. Then start your trimmer. It may take some "feathering" of the throttle to get it going, as you have to remove the air out of the new filter. In the carb, there is also a 10 micron screen. These also get blocked with a sludge from the fuel. Remove the carb and where you adjust your idle speed, that big plate will have one screw in the middle. Remove that big screw and the whole plate will come off. Ensure that you do not damage the gasket, so just remove it slowly. On the carb block, you will see the screen, Hook it out with a needs. In a little bit of gas, put the screen in it and with your thumb nail, rub the screen. Blow it out. Hold it to the light and you should see that it is clear. With and unsharpened HB pencil. Put the screen back in its position and push down on it with the pencil. I find that the pencil works the best and it is the perfect size. Put the carb back on and I am sure that your machine will work much better than new!!
#7
B
bertsmobile1
With new gaskets I hope.
B
bertsmobile1
You have established that you have spark. Where you have stated that you are having problems with it running, Change the fuel filter in the tank. You will need part number 0000 350 3502. The fuel filter is designed to capture water before it goes to the carb. With a piece of wire, pull it out of the tank, and remove it. Try and blow into it. You should have no resistance at all. Put the new fuel filter on it. Then start your trimmer. It may take some "feathering" of the throttle to get it going, as you have to remove the air out of the new filter. In the carb, there is also a 10 micron screen. These also get blocked with a sludge from the fuel. Remove the carb and where you adjust your idle speed, that big plate will have one screw in the middle. Remove that big screw and the whole plate will come off. Ensure that you do not damage the gasket, so just remove it slowly. On the carb block, you will see the screen, Hook it out with a needs. In a little bit of gas, put the screen in it and with your thumb nail, rub the screen. Blow it out. Hold it to the light and you should see that it is clear. With and unsharpened HB pencil. Put the screen back in its position and push down on it with the pencil. I find that the pencil works the best and it is the perfect size. Put the carb back on and I am sure that your machine will work much better than new!!
With new gaskets I hope.
#8
T
The Specialist
As this is the metering side, a new gasket is not really required here, as long as you do not damage the original one that is there. This is where the fuel comes into the carb. They will usually reseal. Your diaphram on this side is usually plastic, which guides the fuel to the screen. If you damage the gasket, then yes put in a diaphram kit. to do that, pour a bit of fuel into a container and put the new gaskets and diaphrams in it. Take apart the carb, remove the old diaphrams and gaskets. make sure all surfaces are clean of old gaskets. fish the new diaphrams our of the fuel container and put back in place. tighten down the screws. When you put the new diaphrams and gaskets in fuel, you will see the air bubbles come out of them. This ensures a seal is done!!
T
The Specialist
With new gaskets I hope.
As this is the metering side, a new gasket is not really required here, as long as you do not damage the original one that is there. This is where the fuel comes into the carb. They will usually reseal. Your diaphram on this side is usually plastic, which guides the fuel to the screen. If you damage the gasket, then yes put in a diaphram kit. to do that, pour a bit of fuel into a container and put the new gaskets and diaphrams in it. Take apart the carb, remove the old diaphrams and gaskets. make sure all surfaces are clean of old gaskets. fish the new diaphrams our of the fuel container and put back in place. tighten down the screws. When you put the new diaphrams and gaskets in fuel, you will see the air bubbles come out of them. This ensures a seal is done!!
#9
B
bertsmobile1
B
bertsmobile1
Considering the price of new gaskets, which the customer pays in any case vs the time it takes to reuse the old ones, for me it is a no brainer, let alone time required to do it again should the old gasket fail to seal properly.
I am a big believer in the do it once, do it right school.
Considering the carb is a pressure vessel it makes no sense to try & preserve a 55¢ gasket.
I am a big believer in the do it once, do it right school.
Considering the carb is a pressure vessel it makes no sense to try & preserve a 55¢ gasket.
#10
T
The Specialist
T
The Specialist
True! but like you will also find, people moan about putting $1.00 into a machine but don't think twice about spending $1000.00 on a repair for their car!! I'm sure you have had it in your shop that everyone wants it fixed for $20.00!! Also, most people are impatient and just want it to work!! Hence- that is why they are doing it at home!!