Stihl MS181 Chainsaw no ignition.

[Philip Osborne]

I have recently acquired a Stihl MS181 chainsaw that is is approximately 4 years old. I was advised by the previous owner that this chainsaw hasn't worked for the last year. I have been online to familiarize myself with the technical details of this saw and have made a start at trying to find out why the saw doesn't work. First I checked for a spark and there was no spark, so I replaced the plug for a new one of the correct type, still  no spark. Then I replaced the ignition module with the correct Stihl replacement and set the gap between the module and the flywheel to the correct amount, still no spark. I have tried it with and without the positive wire connected to the coil, just in case it was a fault in the wiring harness. I have even tried it with an extra earth wire, in case the coil isn't earthing properly, still no sign of any spark. I have even tried it by holding the plug to see if there was any kind of electric shock, but there was nothing. I am at a loss as to what to try next, given that this is a very simple engine, with a basic ignition system. Any help would be greatly appreciated.

[openspaceman]

Is there something preventing it turning over fast enough? These coils don't work below sabot 400rpm.

[Philip Osborne]

I don't think so, I've been pulling the pull cord quite quickly with no plug in, so it has been turning over very fast.

[spudulike]

Strange one, you do need to view the spark in subdued light, pull it over pretty fast and also make sure the plug is earthed on the top of the cylinder.

If you are still not getting a spark, did the new coil come with a new HT lead or was it the old one?

How did you gap the coil to the flywheel? a business card is generally a good method.

If all this has failed, the magnet has failed in the flywheel. This is pretty rare and only seen one before - a MS461 that has a nylon flywheel and the magnets are not the size of the ones on your machine. Generally magnets only fail through age...possibly 20 years+ or through impact with the coil of loose screw etc.

Other than that, check the engine is earthed to the coil with a continuity meter.

[Philip Osborne]

Thankyou for this information. The new ignition module was the genuine Stihl part complete with HT lead.

I used a thin business card (.00115") to gap the coil from the flywheel.

The magnets on the flywheel are surprisingly strong and I have cleaned them thoroughly.

I have added a separate earth from the coil to the engine.

I will go and try it again in the garage in total darkness, giving it a hefty pull like 'Openspaceman' suggests.

Although looking at the video's on Youtube, the operators didn't seem to pull the starter chord excessively hard. I'll let you know what happens......

[Philip Osborne]

Would you believe it, if I pull the starter ridiculously fast it sparks, anything less than that and there is no spark at all. Whether I can pull it that fast to start it under compression with the spark plug in position remains to be seen. Thanks again for the helpful suggestions from both of you, I find these forums are very helpful.

[Stubby]

8 hours ago, Philip Osborne said:

Would you believe it, if I pull the starter ridiculously fast it sparks, anything less than that and there is no spark at all. Whether I can pull it that fast to start it under compression with the spark plug in position remains to be seen. Thanks again for the helpful suggestions from both of you, I find these forums are very helpful.

Could be the flywheel magnets are becoming tiered . Not common but have heard of it . 

[Philip Osborne]

What is meant by 'tiered' is it to do with the strength of the magnet?

[Stubby]

1 hour ago, Philip Osborne said:

What is meant by 'tiered' is it to do with the strength of the magnet?

Yes . 

[spudulike]

He means "tired", the spelling on this forum isn't one of its strong points and Stubby is one of the better ones!!

Your position is a common one and you must pull the saw over pretty sharpish to get a spark on some models. 

On some older machines, a really slow pull is fine and on some like the MS461 and MS660 need an enthusiastic pull.

Sometimes you can overcome weak magnets by closing up the coil to magnet gap by using A4 paper rather than a business card....this will advance the spark by a degree or two as well which you probably won't notice.