Mcculloch MAC 335 loses power and dies..

[clocKwize]

I've recently bought a Mccullock MAC 335 second hand, the guy showed me it working so I thought it was ok and it has been ok..

Once I get it going (which can take a while) its fine for ages. I've cut some large bushes to pieces, all is well.. The first time I've used it, I turned it off for a little while, then tried to start it back up again, and it seems to have no power to move the chain, like when I pull the trigger, it struggles (see video) then dies. If I leave it for an hour or 2, it'll start up fine and be ok again.

The second time I used it, it just plain died after about 30 mins, but I think it might have overheated, if thats possible? It was getting very hot.. The same thing happened again - I left it to cool down for 5 min, then tried to start it, and it idles for a while, sometimes dying, but eventually I get it running more smoothly and then it dies when I pull the trigger.

Anyone have any idea what could cause this?

Video attached of the noise it makes!

Many thanks for reading.

 

[Nozzle]

Have you put sufficient oil in the fuel?
Has the air filter been replaced?
Is the fuel tank full of crap?
Is there a fuel filter you can change?
It will run hot... it's an internal combustion engine!

Nozzle

 

[clocKwize]

I mixed 50:1 (400ml petrol to 8ml oil) as stated on the bottle and in the manual.
The air filter looked pretty clean
I emptied out the fuel before I used it and filled it with fresh - didn't see anything in it
I haven't seen a fuel filter, but I'm assuming there is one somewhere?
I know it'll be hot but obviously there'll be a point where it gets too hot lol

 

[Burnerman]

Can you post up a picture of the side of the carburettor.....in particular, the two jet adjustment screws?
The fuel filter is inside the fuel tank dangling on the end of the fuel supply tube - you can fish it out with a length of stiff wire, bent at the end.
John

 

[foxhole]

You do realise moving the handle back and forth is the chain brake?

 

[clocKwize]

Can you post up a picture of the side of the carburettor.....in particular, the two jet adjustment screws?
The fuel filter is inside the fuel tank dangling on the end of the fuel supply tube - you can fish it out with a length of stiff wire, bent at the end.
John

Thanks - I'l have a look at the fuel filter. The side of the carb:

You do realise moving the handle back and forth is the chain brake?

Trying to be funny?

 

[Burnerman]

Grand pic, cheers!
I'm going to try to explain how to tune the carburetter here - but that assumes that the air filter is clean, fresh fuel and so on ......a new spark plug is always a good idea! Usually there is an air breather on top of the fuel tank that lets air in as the fuel is burnt - this needs to be clean too.
The top screw is the mechanical fast idle.....clockwise speeds the machine up, anti clock slows it down.
The two slotted screws below are the mixture screws......they will be marked L for Low speed and H for High speed. Get some carb cleaner, clean the crap away and determine which screw is which.
The L screw is adjusted first. Get the machine started and ticking over reliably - using the top screw if necessary. Turn the L screw anticlock very slowly, just until the engine starts to slow up a bit. This is giving the machine a rich mixture which is good for it to accellerate. Turning this screw clockwise weakens the mixture - the machine speeds up but doesn't have the power to accellerate. Gently twiddle the screw and see if you can get the machine to respond - but only turn them a tiny bit - you can set them to the original setting as the screws are horizontal here.
If you are happy with the low running speed, the H screw can be adjusted in the same way - but the machine has to be running nearly flat out so clamp the bloody thing down !
If this doesn't work, then its a carb stripdown I'm afraid and we are into a new ball game here - but as you say the machine generally runs well and has performed so for 30 minutes......things can't be too bad!
A sign of a healthy two stroke engine is its compression. Pulling the start cord should give quite a resistance and a nice 'pop pop' sound as you pull.
John

 

[clocKwize]

*lots of very useful info!*

Thanks very much I'll give this all a go tomorrow morning and report back! I bought some carb cleaner today, luckily.

 

[lostinthelight]

It could have had a "lean seize" from the high speed jet being screwed in too far?
litl

 

[Burnerman]

Who knows but I hope not! If the cylinder fins are clean then it shouldn't happen but a weak mixture at the top end isn't good for the machine either. The fact that it starts and idles but won't always pick up usually indicates a carb issue.
Anyway - another word of 'wisdom'......if cylinder issues are suspected, pop the exhaust off and you'll either see nice polished parts or an almighty mess
John

 

[Burnerman]

Thanks very much I'll give this all a go tomorrow morning and report back! I bought some carb cleaner today, luckily.

Check out www.gardenhirespares.co.uk if you like - a replacement pattern carb for this machine is under £20! Can't beat that!
John

 

[foxhole]

Thanks - I'l have a look at the fuel filter. The side of the carb:

Trying to be funny?

No, your video appears to have the brake on, seizing like that is typical of having incorrect oil ratio, add a touch more.

 

[lostinthelight]

No, your video appears to have the brake on.

I must admit when I saw the vid it did look like the brake was on ,I would have expected some juddering of the chain given the revs it sounded to have had it not been on !
litl

 

[Nozzle]

Also - have you got oil in the chain pot too? It's really thick gloopy stuff - and is the chain bar correctly adjusted?

Nozzle

 

[clocKwize]

No, your video appears to have the brake on, seizing like that is typical of having incorrect oil ratio, add a touch more.

Oh, ok, my bad. I realised I had the chain brake on - thats the correct way to start from what I've read - Should I remove it immediately after starting? I read somewhere 40:1 but somewhere else 50:1 - I went for 50:1 - I'll add a bit more to get it to 40:1. Thanks