Strimmer Keeps Cutting Out

Schorpio

Hi all,

I hope this is the right place for this query (it's a bit more mechanical than gardening).

TL;DR - I have an old strimmer that starts and idles, but dies when any throttle is applied.

The strimmer dates from the early nineties. Family has owned it since new, and it's only seen light usage. Was in the shed with no use for about two years before I pulled it out a few days ago. Added fuel (mixed) and it wouldn't start. Fuel was also slowly leaking out of the air intake.

Changed the carb, new fuel filter and replaced the fuel lines. Strimmer now starts fine. If throttle is applied when starting, the head will spin, and keeping spinning as long as there is at least some throttle applied. If no throttle is applied, the engine will idle, but die immediately if you try to apply any throttle.

It seems a bit like the engine isn't developing enough torque to get the head spinning? But the head is free spinning, and doesn't seem jammed or stiff. This seems more like an engine issue.

Any advice would be appreciated!!

magicbastarder

i was going to suggest a gummed up carb when i first started reading, but you changed that…

The Continental Op

For the cost of a spark plug I'd replace that before doing anything else.

Wasted loads of time in the past with identical issues and often putting in a new plug was the solution - but not always :-)

Schorpio

https://www.boards.ie/discussion/comment/122279388#Comment_122279388

Yep. The new one is a no-name cheap Chinese one though, so I'm not 100% that it's definitely not the problem. The fact that it idles and also runs under throttle from a pull start makes me think it's probably fine though. It's just the transition from idle to adding throttle and starting the head spinning.

Schorpio

https://www.boards.ie/discussion/comment/122279404#Comment_122279404

Fair point. I'll give it a go. The one in it currently looks fine visually though, so I don't have high hopes!

You're right though, easy to do and cheap, so why not.

The Continental Op

https://www.boards.ie/discussion/comment/122279514#Comment_122279514

I've thought the same thats why I've wasted loads of time in the past. tbh the plug issue has normally hit me on chain saws rather than strimmers but they are all 2 strokes.

Just because a plug will provide a spark at 2000rpm doesn't mean it will continue to work at 7000rpm (and sometimes faster).

The Continental Op

I've a very cheap no name chinese carb on one of my strimmers and one of my chainsaws. The strimmer one is great but not so sure about the copy on a sthil chainsaw.

From new the strimmer was always a pain to start, poor idle, poor power pick up, easily stalled etc. No end of fettling sorted it and I had it down to its component bits. A £8.99 carb from Amazon fixed all those problems.

standardg60

Also worth removing the air filter and checking the butterfly valve is opening under throttle and not jammed shut.

Also found very gentle throttle at first can encourage them to fire up too.

Schorpio

https://www.boards.ie/discussion/comment/122279820#Comment_122279820

I've a similar experience. A cheap carb worked wonders for my ride-on lawnmower. No issues at all. I am wondering if this carb is working just well enough, but not 100%. But maybe it's a different issue. It's unusual that it will idle fine, and operate under throttle fine immediately from start, but you can't go from idle onto the throttle.

The Continental Op

https://www.boards.ie/discussion/comment/122282754#Comment_122282754

Does sound like a carb problem to me. I'd work on the old one strip it down and blow it out. I'd even think about getting a third one if you can't send the new one back.

Ardent

Well, @Schorpio, did you figure out what the problem was?

Schorpio

https://www.boards.ie/discussion/comment/122327413#Comment_122327413

No! In fact, I made it worse!

Changed the spark plug (brand new Champion plug) and new air filter, and now it doesn't stay going (either on idle or on throttle). It'll run for a few seconds and then die.

I'm convinced that it must be fuel delivery. Quite possibly the new Chinese carb isn't all that. (I don't know, clutching at straws).

Looking at the Original carb, it's a Zama, with "e3 31p" stamped on the side. Google seems to suggest that's actually a Zama C1Q-E3. I'm considering buying a kit to try to refurb the original carb.

The Continental Op

Does the carb have a connection to the crank case? Often a hidden pipe at the bottom of the carb. It uses the pressure of the crankcase to pump fuel. Not all carbs work that way more common on chainsaw than strimmer.

Schorpio

https://www.boards.ie/discussion/comment/122334488#Comment_122334488

Would that be a pipe as such, or could it be a small hole in the carb which aligns when screwed in. It definitely doesn't have the former, but maybe the latter? Fuel tank is on top on the machine, so gravity should do most of the heavy lifting.

The Continental Op

https://www.boards.ie/discussion/comment/122335146#Comment_122335146

The hole is an alternative to the pipe. I needs to be clear as it runs the little diaphragm pump in the carb. I mentioned it as if there is a pipe it sometimes gets missed. I know I've forgotten to reattach it in the past.

Ardent

https://www.boards.ie/discussion/comment/122333684#Comment_122333684

These symptoms sound a lot like what my Stihl strimmer went through a couple of years ago. At the end of the day, I had to buy an OEM replacement carb.

Don't bother trying to refurb the old carb you have, most likely a waste of time. Just buy a quality replacement.

Old codger

after more than 60 years working with small petrol engines I can give you a few tips. Firstly check your new Chinese carb and look for one or two small adjuster screws on the main body. If you see these adjustable screws that used to have a plain slot for adjustment and now require a special tool ( to comply with emissions and deter owners from fiddling) these would need to be screwed home , carefully, and then unscrewed by three half turns as a starting point. Then turned slightly clockwise to reduce fuel and anti clockwise to increase it. If you have two screws the one nearest the cylinder is a slow jet adjustment, affecting fuel supply up to half throttle, the one farthest from the cylinder is the main jet and controls full speed supply. If you don’t have a set of special tools and can manage to take the screws out you could cut a slot with a junior hacksaw for a small screwdriver. But don’t mix them up. getting them out will be difficult as there are many different versions of the screw type. after all this,the addition of ethanol E10 to petrol is causing major problems to carbs and the plastic and rubber components of the fuel systems, especially in tools that lie idle for weeks or months at a time. partially or completely blocking the internal fuel galleries in the carbs.

I used to have to replace maybe three or four carbs a year, now it can be up to thirty or more. After market carbs can be less than proper original makers ones and although cheap are not always successful.