Stihl HS45 hedgetrimmer won't start

[rogerzilla]

It was always a bit reluctant when cold - has always started easily when hot.  I've changed all the filters, coil pack/HT lead and spark plug.  Have also checked the earth (stop) wire, which doesn't seem to be shorted.  Could it be the fuel?  I'm using Aspen 2 but it is a year old.

[Little Jim]

Is the carb clean?  I have never dismantled one of these small petrol engines but my brother is a keen tinkerer of these and he is always complaining how the fuel eventually "gums up" the carburettors on them.  I must admit that I gave up on my ancient (20 years plus) Efco hedge trimmer last year and bought a Sthil battery one.  Bliss.  Starts first time and no exhaust fumes to breath all day.

[rogerzilla]

I gave it a good shot of carb cleaner but it's possible.  I did drain the fuel and run it to empty before winter, as recommended - stale fuel is known to stick the reeds together.  There is a good spark.

[Little Jim]

I did discuss using a carb cleaner or stripping down my hedge trimmer with my brother before I decided to leave it as a "future project".  He thinks that the carb cleaners only do so much and the results are much better if you strip them down, but then he loves doing that sort of thing.  I seem to remember him talking about a small diaphragm in the carbs on these machines which are prone to splitting, but I could be wrong, he talks for hours about them and I start to lose concentration 

[rogerzilla]

After trying a tip found elsewhere (only prime a warm engine) it fired up and ran for about 30 seconds at idle before dying.  It's increasingly looking like stale fuel that's lost its volatiles.    I'll have to start using normal petrol and 2-stroke oil mixed in small quantities, because I can chuck leftover petrol in the car before it goes sour.

[Invicta]

I would be surprised if it's the fuel as you're using Aspen 2, which has a much better shelf life than pump petrol, years rather than months. I use Aspen in my chainsaw, don't empty the tank in the Spring, and it starts in the Autumn without any problem. Sounds like you've sorted any possible ignition problems, and if it runs for a bit then compression should be OK. So probably fuel related, but maybe the fuel system rather than the fuel itself?

[rogerzilla]

I reckon it'll be ok if enough fresh fuel gets through to clean it out.  I had to step away to get my ear defenders, or I would have blipped the throttle to keep it going until it was properly warmed up.  The Aspen does seem to go off - I had a 'mare starting it one day last summer, but changing the fuel in the tank instantly solved it.

[mrcharly-YHT]

Fuel line?

Are you absolutely sure that the fuel line is not compressed/kinked or otherwise obstructed?

Has the throttle control slipped?

[Tim Hall]

This may help

https://www.youtube.com/watch?v=m6zoW5Uc4F4

Although on reflection it probably doesn't.

[rogerzilla]

Fuel line?

Are you absolutely sure that the fuel line is not compressed/kinked or otherwise obstructed?

Has the throttle control slipped?

The primer bulb fills fine and, after repeated cranking, fuel drips from the exhaust, so it is definitely getting through.  Will try starting fluid.  I reckon it will be ok if I can get it to run until it's fully warmed up, with some WOT use.

[Tim Hall]

More usefully my two stroke Mountfield mower wouldn't start despite much pulling and Bad Swears.

The carb is a very simple affair, bowl held on my a bolt through the bottom. Took that off, managed not to get entirely covered in Petril, and tipped much crud out of it.

[andytheflyer]

As a restorer and rider of classic motorcycles, and an ex-petrol powered model aeroplane flyer, I believe I have some experience of carburettors.

I'd suggest it's very likely to be a partly blocked pilot jet in the carb. Carb cleaner will only do so much.  It needs a strip, a soak and a re-build.  Carbs are much more finicky now with modern fuels - it's a major issue for the classic motorcyclists.  Ethanol in fuel (aka effinol) rots the fuel lines, primer bulbs and the clunks (the weight on the end of the pickup line in the tank. The muck that then gets into the fuel clogs up the carb jets. 

Get a new gasket kit, strip the carb, thoroughly clean it, blow through all the jets (and even poke some fine brass wire - or better - plastic 'wire' into the jets and wiggle about - carefully - you can easily wear away the jets). If you have spark, good fuel and compression, and the jets are clear, it'll run.

I run my bike carbs dry at the end of the season and drain the tanks so the fuel system is dry over the winter.

[rogerzilla]

Aspen 2 has no ethanol.  The carb looks spanking inside, too.  I reckon it is a gummy jet, which fresh fuel should clear if I can just get it running.  It's not worth rebuilding Stihl carbs; you buy a new one.  I don't think there is a rebuild kit as such.  This is also a 2-stroke reed carburettor, something I know little about.  I am ok on fixed-choke automotive carbs.