Chainsaw issue

I have a McCulloch 360T Starts fine .. either hot or cold ... which in itself is a good indicator that many things are Ok with the saw.
In use ... be cutting fine then revs will die, then get to a point with chain out of the wood .... tickover is fine, but when I try to rev it picks up, but after about 20-30% of power then dies off ... often to a stall. It can often take 10 or more attempts before it will get to point that revs will open up .. then it cuts fine ... but a few minutes later it will start again.
When it is revving it cuts fine with no loss of power.
I have cleaned air filter, checked plug gap, used new fuel, general clean to get rid of any oil or wood chip build up.
Any tips ?
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Chain jamming or chain brake fault? I presume you’re using the correct oil/fuel mix and the engine isn’t tightening up? How about the chain oiler? Is it consuming oil at the expected rate?
Tim
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On 12/01/2019 14:31, Tim+ wrote:

Possibly although my money would be on Chris and Harry's suggestions of a fuel blockage.
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Inclined to agree. ;-)
Tim
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Tim+ pretended :

I agree - it sounds as if it is running out of fuel, despite fuel in tank. Check the fuel pickup pipe in the tank - if should be flexible and have a weight in the end, so gravity keeps it in the fuel.
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On Sat, 12 Jan 2019 14:04:56 +0000, rick

Sounds similar to a problem I had with a petrol mower. Turned out to be dirt in the fuel line and a partially blocked fuel filter.
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Chris

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On Saturday, 12 January 2019 14:05:07 UTC, rick wrote:

Check fuel tank/filter for debris/chippings blocking outlet pipe.
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On 12/01/2019 15:06, harry wrote:

Any idea how to get to that ?
I just took plug out again .. nice biscuit colour so all seems well there. Used compressed air to blow through carburettor breather pipe back to tank - all clear.
Carburettor is a Zama W26 .... not sure if it has a diaphragm or not, if so I suppose that could be suspect.
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On Saturday, 12 January 2019 15:32:20 UTC, rick wrote:

With many chainsaws, the "carburetor" is in fact a fuel pump worked off crankcase vacuum. So it will work in all positions.
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just had the same thing on a leaf blower new diaphragm fixed it
-
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Very common problem with small two-stroke engines. Usually turns out to be gunk in one of the carburettor passages or apertures.
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Evremonde

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On 12/01/2019 14:04, rick wrote:> I have a McCulloch 360T > Starts fine .. either hot or cold ... which in itself is a good > indicator that many things are Ok with the saw. > > In use ... be cutting fine then revs will die, then get to a point with > chain out of the wood .... tickover is fine, but when I try to rev it > picks up, but after about 20-30% of power then dies off ... often to a > stall. > It can often take 10 or more attempts before it will get to point that > revs will open up .. then it cuts fine ... but a few minutes later it > will start again. > > When it is revving it cuts fine with no loss of power. If you quickly loosen the fuel cap after it has died does it suck air? Similarly will it run for longer if the tank is half full rather than full?> > I have cleaned air filter, checked plug gap, used new fuel, general > clean to get rid of any oil or wood chip build up. > Always a good idea to have a new plug available, I have one here that runs for 20 seconds then stops, it had me fooled for a long time as I thought the fault was in the coil.
Apart from vacuum forming in the tank there are a couple of things:
1 cracked or leaky impulse line, this is the bit that communicates from the crank case to the diaphragm pump in the carb, some say these deteriorate due to increased ethanol in fuel.
2 blocked filter in gallery between pump and needle valve in carb, this is a metal mesh. Occasionally this can also trap a blob of water which leads to erratic behaviour.
AJH
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On 12/01/2019 14:04, rick wrote:

That would be the symptom if the fuel tank air vent was blocked.
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Sounds like you have something in the carby that moves around and blocks the jet when you get the loss of power.
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On 12/01/2019 16:56, Jim K.. wrote:
Need a special tool to remove H & L adjustment screws (mixture) as they are splined - just ordered one ..... I'll remove and see if any gunk in them.
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