Petrol hedge trimmer questions

18 Mar 2005
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United Kingdom
I have two petrol hedge cutters and just wondered if someone can advise on how to make them run perfectly.

One is perfectly usable and I do use it often - I'm just not sure it runs perfectly!

The manual says to prime 7 times then start on full choke until it fires then start without choke.

However if I start on full choke it fires up and runs on full choke (but won't rev) I can then move the choke down to half way and it runs and revs and I can use the hedge trimmer. If I turn the choke all the way off even after it is fully warmed up then it will idle but sounds like it bogs down if you try and rev it and will cut out if you keep trying.

It starts easy enough - do I just ignore it and be happy that it runs!?

The second one is a bit more of an issue.

I haven't got a manual so have just been going with 7 primes, I changed the fuel pipes as I had a bit of a leak and it now primes up perfectly. If I start it on choke you can hear it catch so I then turn the choke down - if I turn it to half way like the other one it won't start but if I turn the choke all the way off then it will start and revs for about 5 seconds then cuts out, it seems to flood and then becomes hard to start again after that.
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Both machines suffer from fuel issues (obviously) and both need attention to their carburettors.
The machine make would be handy and the type of carb. they have.....for example whether they have any adjustment screws, maybe marked H and L.
Pictures are a massive help!
Things to do first - clean the air filter elements, fish out the fuel filters from the tank with a length of hooked wire and clean them. Next, see if you can find any vent into the fuel tank which allows air in.
One big issue with hedge trimmers - especially the small engined ones - is to loosen the blade clamps - any undue tightness here is guaranteed to stall the machine.
The next stage involves an aerosol can of carb cleaner and a compressed air supply if thats available.
John :)
I don't know specifically about petrol hedge trimmers, but I do have a couple of chainsaws and the start procedure is:

1) prime fuel system using the bulb
2) pull out choke to full, also engage high idle
3) pull on starter until you hear a "cough" or a slight running on its own for a couple of rotations*
4) put choke back in (but leave at high idle setting)
5) pull on starter until it starts and revs cleanly
6) 'blip' the throttle to disengage high idle and return to normal idle

* is difficult to describe in words, but there's loads of Youtube videos around showing how to start a chainsaw (and probably similar ones for a hedgetrimmer) so have a look/listen to these.

The 2nd hedge trimmer, what you need to do is get it running and warmed up, then rev it at full revs for about 30 secs-1 minute with no load on it (not sure on hedge trimmers but a chainsaw doesn't have a rev limiter, so full revs with no load is about 2/3 - 3/4 throttle, full throttle with overspeed the engine. You'll kinda know from the engine note what is 'full'). This thoroughly warms all parts and gets a good flow through the carb, head and exhaust, clearing it out. It may well need an adjustment on the mixture but I'd try that first. Its going to be hard to tell if its running lean or rich, if you adjust the mixture. Probably wise to try it in small steps and sense if its getting 'better' or 'worse' etc then aim for the happy spot.
PS my Husqvarna chainsaw's controls incorporate choke and high idle together. Your hedge trimmer may not have this type of control and you'll need to separately set each, to start it.
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Thats the appropriate technique for starting any two stroke......with some hedge trimmers there isn't a locked fast idle, but its easy enough to hold the throttle on full when pulling the recoil starter.
I hope these machines aren't McCullogh!
John :)

They're nothing expensive but not McCullogh - can't remember the make and not near them at the moment.

I have a large compressor for air but I don't think I've got any carb cleaner - might have some brake cleaner spray.

I forgot aout the throttle part, both have the mech broken to hold full throttle on. With the working one I just hold the throttle on when I start it up.

With the non working one I've disconnected the throttle cable at the moment due to it not working quite correctly so have just been turning the throttle control on the engine.

I currently have the air filter removed on the non working one as I was getting some fuel coming out of the air intake and it soaked the air filter.

Both have two adjustment screws for fueling but I haven't touched these.
As these machines typically run at all sorts of angles, they don't have typical carburettors with float chambers.....instead they have diaphragms that pump the fuel (with a convential needle valve) and another one that controls the fuel metering. All carbs have very fine filters inside.
If the carb screws have springs on them, one turn out from fully in will get you going, ready for a fine tune.
Typical carb makes are Zama and Tillotson but there are others.
John :)
Thanks I'll take a look.

IIRC the screws have a rubber tube over them so can't really see if they have springs or not.

I take it that you screw them both in clockwise then back out anticlockwise one turn?

I'll take a look to see if I can work out what make the carbs are.

I take it the reference to the fine carb filters is that they need dismantling to get to them then use carb cleaner / compressed air to clean?

The rubber tubes are there to keep the crap out from the air cleaner box so the screws will be adjustable. Its clockwise to turn in and weaken, anti clock to richen the mixture. You can remove the screws completely for cleaning out their individual jets.
Inside the carbs, the filters are gauze, and there are quite a few drillings to blow clear.
One word of caution though, some carbs have blanks called welch plugs inside which can be blown away with too much air so care is needed there.
John :)

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