Warm chainsaw would not start

[s.varty]

This may sound obvious, but check the cheapest to replace first,,spark plug

[openspaceman]

Coils sometimes struggle when hot, I think.

 

Wouldn't they just cut out when it is running then?

 

Husqvarnas in the 70s and 80s had a problem with vapour locks if you got them very hot, switched them off and left them for a few minutes.

[skyhuck]

Wouldn't they just cut out when it is running then?

 

Husqvarnas in the 70s and 80s had a problem with vapour locks if you got them very hot, switched them off and left them for a few minutes.

 

Not sure (I'm no expert) but I would imagine a weak spinning coil on a running saw will produce a better spark than a weak coil just being pulled.

 

Easy to test, just get warm and then remove HT lead and check spark when pulling.

[gensetsteve]

Not sure (I'm no expert) but I would imagine a weak spinning coil on a running saw will produce a better spark than a weak coil just being pulled.

 

Easy to test, just get warm and then remove HT lead and check spark when pulling.

 

I have come across coils that struggle when hot. Not sure if there is less magnatism when hot, the coil has less insulation when hot or if the air gap between rotor and stator changes with heat expansion. Or it could be a rich mixture which floods saw when hot but helps when cold.

[GardenKit]

Coils fail in many ways, but itbis not uncommon for a spark to be too weak to start, but strong enough to run, as has been said.

 

I am not clear on this one if the OP is on fresh fuel or still using the winter fuel.

 

If he is on 'winter grade' fuel, even if it has not gone stale then it could cause hot start problems due to fuel vaporisation (vapour lock)

 

Before getting too carried away with coils etc, change to fresh fuel, which will by now be 'summer grade' and see if this solves the problem.

[spudulike]

I have come across coils that struggle when hot. Not sure if there is less magnatism when hot, the coil has less insulation when hot or if the air gap between rotor and stator changes with heat expansion. Or it could be a rich mixture which floods saw when hot but helps when cold.

 

The issue with hot coils is the breakdown of insulation of the coils or components due to heat. Typically the coil will either give a couple of sparks if left to stand idle for a while and then nothing at all or the saw will start to misfire when hot ending up in spark failure.

 

The OPs saw sounds like possible low compression - this can cause a saw to have enough cold compession to start but not enough when it is hot and has dropped 20psi. Most likely the No1 choice.

 

The saw may have nipped up at some stage so a check of the piston through the exhaust port would be a pertinent check.

 

The tank vent can cause some pretty weird running but mostly almost immediately if completely blocked and most commonly after a few minutes.

 

Spark plug - possible as I recently had one go from good to bad in minutes of running and heat may effect spark.

 

If it does it again - When hot, check for spark, check the plug is damp/wet after trying to start it - other then that, make sure the saw has lots of good spongy compression when the saw is pulled over top dead centre slowly.

[chainsawMal]

Of course make and model will also help.....

 

Its a Chinese model and fuel was left in it all winter.

 

And yes, fresh petrol being used!

Edited May 18, 2013 by chainsawMal

[Rich2484]

Its a Chinese model and fuel was left in it all winter.

 

Wait for it..........

[Eddy_t]

Buy a new one, you won't get parts

 

 

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[chainsawMal]

Is it better not to start with a cheap saw and work with it first to learn all mistakes on it than a good quality high priced saw?