Stihl HS45 hedge trimmer no-start

[Guineafowl]

Was previously running, but when my mate went to use it this time, no start, so he brought it to me.

No spark. Tried a known good plug, disconnecting the kill wire, regapping the coil to flywheel (0.012”). Still no spark.

New coil, non-genuine (genuine was out of stock). Spark!

Still won’t start. All I can get is the occasional spit out of the carb or exhaust side, even with easy start and fresh petrol.

- Checked flywheel was still keyed in the right place.
- No airflow blockage in exhaust or carb side. It’s getting fuel, as the plug gets wet.
- Compression reasonable, by feel.

So I’ve got spark, fuel, compression, timing, airflow. And a sore right arm.

What else can I do? Genuine coil now ordered, but the fake one gave a spark…

 

[Barking Mat]

Pop the spark plug out and check the piston for wear.

My Stihl chainsaw seemed to have compression, but it was worn.

How old is it ?

Air filter newish ?

 

[Guineafowl]

Pop the spark plug out and check the piston for wear.

My Stihl chainsaw seemed to have compression, but it was worn.

How old is it ?

Air filter newish ?

2004. Air filter reasonable. Took it out to spray in the easy start.

Bring the piston up top and rock it side to side with a screwdriver?

Bore looks ok, from the ports.

 

[Barking Mat]

Won't even pop with easy start ?

 

[Guineafowl]

Won't even pop with easy start ?

Not consistently. It’s acting a bit like a no spark, a bit like a timing issue.

I wonder if the fake coil is too feeble to spark under compression, or perhaps is somehow timed differently from the real one.

 

[Turbo]

If it doesn't start with a squirt of WD40 in the carb (easier on the engine than easy start) then you still have a spark problem.

 

[Barking Mat]

I used a business card as gap for the coil on my chainsaw, too close isn't an issue, is it a bright spark ?

 

[Guineafowl]

If it doesn't start with a squirt of WD40 in the carb (easier on the engine than easy start) then you still have a spark problem.

It was brake cleaner to start with, then when that didn’t work I actually bothered to dig out the easy start. Will try WD40 in the future, ta. I don’t like hearing that KNOCK when it fires.

I used a business card as gap for the coil on my chainsaw, too close isn't an issue, is it a bright spark ?

Again, couldn’t find a business card so got out the feeler gauges. Not that bright, more like a static leccy spark. Hard to tell in the daylight. Do I need to get a spark tester?

 

[Barking Mat]

Well I really don't know.

I'm not a top authority on two stroke stuff.

But IME at 20 years old, get a pro in a garden centre to diagnose it, and start looking at a new Chinese Amazon £40 engine, was the route I ended up going down.

Get a pro to check it out first, and then proceed.

Sorry I can't help more.

 

[Guineafowl]

Well I really don't know.

I'm not a top authority on two stroke stuff.

But IME at 20 years old, get a pro in a garden centre to diagnose it, and start looking at a new Chinese Amazon £40 engine, was the route I ended up going down.

Get a pro to check it out first, and then proceed.

Sorry I can't help more.

Not at all - thanks for your help. Looks like a crappy coil. At least I haven’t missed something silly.

 

[Barking Mat]

Not at all - thanks for your help. Looks like a crappy coil. At least I haven’t missed something silly.

My brother's a tree surgeon, he won't fit anything which isn't Stihl as it's all Chinese 'poo', he's very opionated.

I've had no issues with cheap carbs, engines and stuff, but I'm an occasional user, I find it easier to order a ten quid carb, rather that try to diagnose and repair, too small, fiddly and sensitive.

 

[Old Dog]

You sure its not flooded? Stihl's are a real pig to start if it's been flooded. Take the plug out hold it with the piston pointing down and keep turning it over with the pull cord. Warm the plug before you refit it. Check the primer bulb for pulling air into the carb.

 

[angellonewolf]

to be fair you taken it a good and cheaked most of the normal problems

put back the original coil back on (as long as you have spark with it )


and then remove the exhaust then easy start then try untill it coughs half choke and should run for a secs

if not that not much more you can do (the carb can be chucking in way more fuel than needed and stoping it only way to test this remove the fuel pipes (and as above but only had this once)

 

[Guineafowl]

You sure its not flooded? Stihl's are a real pig to start if it's been flooded. Take the plug out hold it with the piston pointing down and keep turning it over with the pull cord. Warm the plug before you refit it. Check the primer bulb for pulling air into the carb.

I did have the piston at BDC and blew in compressed air for a bit, in case of that.

I’ll give it a try tomorrow.

I find these older 2 strokes have their foibles. For an unknown machine:
-choke on, throttle off, pull till it farts.
-choke off, throttle trigged half, pull till it starts

Usually works.

 

[Guineafowl]

to be fair you taken it a good and cheaked most of the normal problems

put back the original coil back on (as long as you have spark with it )


and then remove the exhaust then easy start then try untill it coughs half choke and should run for a secs

if not that not much more you can do (the carb can be chucking in way more fuel than needed and stoping it only way to test this remove the fuel pipes (and as above but only had this once)

Original coil completely dead, as far as I could work out.

I did have the carb apart as well, not a full rebuild but a quick look and blowout. Also checked the H/L screws were reasonably set. I didn’t get too far into that as the problem was a dead coil, so why fiddle with the carb? Desperation, in my case.

 

[Guineafowl]

Does it have a flame trap in the exhaust? That can get blanked off, if there.

Like a spark arrester screen? No. Exhaust seems clear.

 

[angellonewolf]

Original coil completely dead, as far as I could work out.

I did have the carb apart as well, not a full rebuild but a quick look and blowout. Also checked the H/L screws were reasonably set. I didn’t get too far into that as the problem was a dead coil, so why fiddle with the carb? Desperation, in my case.

ok try the same with the china carb see if that comes any differance

 

[JOEPRO]

Was previously running, but when my mate went to use it this time, no start, so he brought it to me.

No spark. Tried a known good plug, disconnecting the kill wire, regapping the coil to flywheel (0.012”). Still no spark.

New coil, non-genuine (genuine was out of stock). Spark!

Still won’t start. All I can get is the occasional spit out of the carb or exhaust side, even with easy start and fresh petrol.

- Checked flywheel was still keyed in the right place.
- No airflow blockage in exhaust or carb side. It’s getting fuel, as the plug gets wet.
- Compression reasonable, by feel.

So I’ve got spark, fuel, compression, timing, airflow. And a sore right arm.

What else can I do? Genuine coil now ordered, but the fake one gave a spark…

Yep a new aftermarket ignition coil was giving alot of trouble on a 2 stroke of mine and as soon as a genuine coil went back on ran perfect.

It may be fine when you get the genuine coil I'd leave it alone until that arrives.

 

[Guineafowl]

Right, the bloody thing’s working, and I can close this out. Thanks for the advice.

Genuine Stihl coil fitted, and it started second pull.

The aftermarket coil was sparking in free air, but not in cylinder. I’ve heard of this, but never seen it. Tricky to diagnose, but as someone pointed out, if it doesn’t fire with easy start (+ compression), it’s a no-spark, regardless of what happens with the plug out.

 

[arther dailey]

the one thing I have found with sthill is there is a micro filter on the fuel pipe in the tank , this eventually blocks , so pays to remove and try , if it works without buy new.