Help Troubleshoot Old McCulloch

[Stubby]

17 minutes ago, Witterings said:

 

Are all tank vents like the one in this video at 2 minutes to save going through the whole thing

 

 

 

Or are some built into the fuel cap .... not sure if it's relevant but the little bit of plastic that attaches to the lid and goes into the fuel tank to stop it rolling away when you take it off, there's a little twirly bit (I'm sure that's the  technically correct name for it 😄 ) that inserts into the lid and it's come away ... not sure if that could have anything to do with it but thinks it's probably unlikely?

It will be something similar to the photo . it will be somewhere on the uppermost flat surface of the tank .

[Fatboy2017]

See parts list attached, maybe some use for you.

mccullochmac335maccat435.pdf

[Witterings]

4 hours ago, Fatboy2017 said:

See parts list attached, maybe some use for you.

mccullochmac335maccat435.pdf 350.3 kB · 5 downloads

 

Brilliant and thank you !

[spudulike]

I would say you have one of two issues, either the piston has been nipped up - taking off the muffler and posting a pic will tell us straight away.... the piston should be smooth and grey with no score marks.

The other issue may be fuel delivery - first thing to do is get a new fuel filter on the fuel line and then try the saw again. If it plays up, try giving the H screw 1/2 turn anticlockwise and see what effect it has. The saw will either go all boggy and struggle to rev out which is the normal effect or, which I suspect may happen, the saw will rev out as it should. 

Small saws often struggle to rev out when they are set lean, big saws over rev and start screaming...not always but often. If the 1/2 turn thing works, try turning it a bit more until the saw doesn't rev and then turn the H screw clockwise 1/4 turn at a time until the saw revs as it should but doesn't scream and has a slight "Burble" or "four stroking" as it is known when revved flat out.

The other issue may be wood chip in the carb gauze strainer - typically under the alloy cover held on with a single large screw on most small saws - best to prize it out and look at it against bright light with a magnifying glass as you can get fine scum in the open areas that is hard to see.

Pic "B" is a nipped or lightly seized piston and what you don't want to see - it typically happens on the hottest exhaust side of the cylinder so removing the muffler is usually the first thing to do.

 

[Witterings]

I think I've decided after all it's probably beyond me only because I don't know how to troubleshoot / identify where the problem is and could just end up buying replacement parts for bits that don't need replacing.

 

I did discover the air vent is a breather in the fuel cap and blew it out with compressed air, I also tried messing around with the idle / high / low but as it was running for a while it got so that it just wanted to cut anyway irrespective of if it was under load or not.

I've found someone just down the road where's it's not expensive for them to at least assess what it is and if it's worth repairing and will take it from there.

 

Thanks to everybody for their input though .... much appreciated as always!