Problem with chainsaw ignition circuit.

[sparer]

I have a McCulloch CS340 chainsaw that cut out the other day and hasn't run since. It has petrol in. It has compression... but it doesn't have a spark. I removed the spark plug and earthed it to the head and pulled the starter cord... no spark. Replaced the spark plug ... no spark. Replaced the ignition coil and also the flywheel with new components. Still no spark. I removed the wires that short out the coil when you want to stop the chainsaw but still nothing. I'm now stumped. Is there something i'm missing?

 

[Burnerman]

Try again, this time in darkness if you can.....the spark may be very faint but blue. The gap between the igniter unit and flywheel magnets need to be about the same thickness as a piece of card, so check that too.
Are you getting a genuine earth to the engine....so many plastic parts and rubber mounts in the way! I use a thin wire with tiny crocodile clips from the plug side electrode to the engine directly.
John

 

[sparer]

The gap between the coil and the flywheel is perhaps a little too large. I'll check that and try to get a better connection between earth and the spark plug then i'll come back.

 

[Burnerman]

The power of the magnets on the flywheel often makes setting the gap difficult.....I place the card between the flywheel magnets and the igniter and then tighten the igniter screws. Pulling the card out with pliers gives the correct clearance.
For sure, if the replacement parts are new I can't suggest much more!
John

 

[sparer]

After regapping the igniter it fired up after a lot of attempts. I now think it's probably carburettor related or the seals around the crankshaft as it will only run properly at full throttle (if you can get it there). I think I'm going to give up on this one as I spent a whole day on it. Time for a new shiny one. Thanks for the advice anyway John.

 

[Burnerman]

Most welcome.....a sure sign of crank seal failure is oil behind the flywheel and usually bearing wear that you can feel.
Good luck with the next one.....how about a shiny new Stihl or Husqvarna
John

 

[sparer]

I think the McCulloch was made by Husqvarna. I was buying Husqvarna parts for it. It was *factory* refurbished when I bought it but it never really ran properly. When I disassembled it, the rubber seal between the crankcase halves was missing and it was sealed with a kind of hard silicone so I was probably onto a hiding before I started. I'd like a stihl but they're a bit pricey

 

[Burnerman]

Worth keeping a look out for offers on a MS180 or similar.....grand wee saw.
John

 

[mwatsonxx]

I'd like a stihl but they're a bit pricey

My stihl is over 30 years old and its had a lot of use, never been serviced, new spark plug every now and then. When I bought it new the guy said golden rule of 2 strokes, when you've finished your work empty the fuel tank and run the saw it till it runs out of fuel. Works for me, stihl everytime.

 

[sparer]

So I bought a Husqvarna 236 (I know, I know...should have bought a Stihl) and it is almost identical to my old McCulloch except that the new chainsaw has way more compression so I'm guessing that was the problem with the old one. Might buy a new piston ring and keep it as a spare

 

[Burnerman]

Husqvarna are excellent products, and buy with confidence......it's a good move to use their own oil though.
If I'm doing a quick assessment on any two stroke, I remove the exhaust and take a peek at the piston.....any scuffing around the ring area means the piston and barrel are scrap.
Good luck with your saw.....if it doesn't get much use, Aspen fuel or equivalent is a good buy.
John