McCulloch mh542p hedge trimmer - h adjustment

[Bilabong007]

Hi,

Was hoping someone could tell me how to adjust the h jet properly on a mculloch hedge trimmer.

I have a tachometer, but I'm guessing at where to tune it to. Spec sheet says max torque at 8-9k rpm, but it's running really rich at this speed with throttle wide open. Where would it be safe to take it to?

It's the first time I have ever worked on an engine, been very good fun. It hadn't ran in 10 years and I rebuilt the top end, gearbox and ignition system.. Started 2nd pull Shame I forgot to write down the carb adjustments before dismatling it...

Thanks

Graeme

 

[Burnerman]

With the machine running fast, hold the throttle there and turn the H screw anticlockwise so the machine starts to 'four stroke'.....slightly misfiring.
If it's already doing this, turn the screw clockwise 1/4 turn and try again.
This means that under load, the machine will 'two stroke' again and give you maximum power.
If the machine is set too rich, the machine will throw out a bit of smoke and not reach peak revs. If it's too weak, it won't develop full power when cutting and start to struggle.
I don't have a manual for this but usually one full turn out from fully in gets you started.
John
PS do take the bottom plate off the machine and grease the mechanism....most important and largely ignored.
J.

 

[Bilabong007]

Thanks for that John I will tinker later today.

So if it tune it up should I worry about engine rpm? I thought if I lean up the mixture I could over-rev it. The manual doesn't state it's max rpm, its not the best of machines...

Thanks

Graeme

 

[Nige F]

turn the H screw anticlockwise so the machine starts to 'four stroke'.....slightly misfiring.
If it's already doing this, turn the screw clockwise 1/4 turn and try again.

I don't have a manual for this but usually one full turn out from fully in gets you started.
John
PS do take the bottom plate off the machine and grease the mechanism....most important and largely ignored.
J.

John - does the in/weak out/rich screw apply to "most " 2T hedgecutters ? I've got one that won't rev. ( a freeby) thanks, Nige.

 

[Burnerman]

I wouldn't worry about maximum revs off load - the machine revs will reduce when it starts to work anyway.
When I'm setting the things up, the machine should accelerate to maximum pretty smartly, (bzzzzzz ) and then slow up a bit as it four strokes (brrrrrr ).
Well done for tinkering anyway - the machine obviously starts well and that's very important.
Do use a quality two stroke oil such as Stihl or Oregon to keep it sweet!
John

 

[Burnerman]

John - does the in/weak out/rich screw apply to "most " 2T hedgecutters ? I've got one that won't rev. ( a freeby) thanks, Nige.

Yep, that's about it, Nige - but some carbs have one screw (Chinese Xenoah) which controls the mixture right across the rev range, some have none at all.
Cleanliness is vital with these things - all have some sort of gauze filter, all have diaphragms which pump the fuel and meter it to the jets. Everyone gets beaten occasionally though, and the likes of GHS Ltd have many replacements. I've just sorted an Aldi hedge trimmer - stripped the carb 4 times And found nothing, it wouldn't idle for love nor money. A £20 carb sorted it completely - which shows I am an expert at wasting my time!
John