Stihl 151TC Erratic runner.

[Chainsaw Mick]

Has anyone had issues with 151?
Have one that soon as it gets warm it runs erratically. Turn it on its side and revs pick up hold it normally and the revs return to idle.
I’ve stripped it down to pressure test it and it seemed to hold pressure fine. Coved it with soapy water and no bubbles. Reassemble it checking manifold sealed properly, and impulse line.
Yet it still runs as it did before.
Apparently it is only 12 months old. Done this from new, dealer replaced carb’ and said nothing was wrong. Another shop has supposedly replaced carb again.
Any ideas?

 

[Woodpecker]

Best idea would be to bin it and buy an Echo 2511t…. On a more serious note have you tried a vacuum test?

 

[Stump Shot]

Generally speaking that's a sign of a seal starting to go out. Some will pass a pressure test, but not a vacuum test.
If not that, find the thing that is changing when tilted and not tilted, like a hole in a fuel line or manifold or a kinked fuel line etc..

 

[Wonkydonkey]

it maybe obvious, but as you don’t say you did it…

Don’t forget to rotate the crank while doing the p&v test

btw does it only increase the idle when on one side ? And not the other. As this is another way to possibly determine which crank seal side is causing the issue..

 

[Chainsaw Mick]

Best idea would be to bin it and buy an Echo 2511t…. On a more serious note have you tried a vacuum test?

Repairing it so I don’t have that option. But I agree. Small echos are amazing and very rarely fail.

 

[Chainsaw Mick]

Generally speaking that's a sign of a seal starting to go out. Some will pass a pressure test, but not a vacuum test.
If not that, find the thing that is changing when tilted and not tilted, like a hole in a fuel line or manifold or a kinked fuel line etc..

It was such an ordeal to make blanking plates I did pressure and vacuum. Only thing I’m not sure I did was rotate crank. DOH!

 

[Chainsaw Mick]

it maybe obvious, but as you don’t say you did it…

Don’t forget to rotate the crank while doing the p&v test

btw does it only increase the idle when on one side ? And not the other. As this is another way to possibly determine which crank seal side is causing the issue..

You could be right with crank rotation, don’t think I did that.
But to answer you question, increased when flipping to both sides.

 

[Stump Shot]

You could be right with crank rotation, don’t think I did that.
But to answer you question, increased when flipping to both sides.

Also can check to see if the weighted fuel pickup is hung up and essentially going dry, this will usually not have instant effect as I think you're describing though.

 

[Wonkydonkey]

I'm Not trying to smart.. but adding to stump shot's reply as well..
you should be testing with a full tank of fuel..

this can help with tank related problems as well as tuning the saw.
It could be a pin hole in the tank part of the fuel line but it could be on the outside of the tank fuel line.
I think someone got a syringe in one end of a fuel line and stretched it while the other was blocked off, thus showing a pin hole that would have been missed.. which was very similar to my 044.

that being said the 151 has a long fuel line with connectors underneath that plastic..



We’re just trying all the obvious that we would do automatically..

a vid uploaded to YouTube with the link posted here may help ?..