Stubborn Chainsaw Running Issue

[Muddy42]

I have a 6 year old Husqvarna 135, that I was given by a friend after he couldn't solve the issue below.  I am pretty sure its been looked after and its been run almost entirely on aspen.

 

The piston looks "used" but not terrible. The starter cord feels like it has enough compression.   It starts well and has as much cutting power as you would expect for a small saw.  I've replaced the fuel filter, air filter and spark plug.  Ive checked and cleaned out the fuel tank.

 

However it has two stubborn issues. Firstly it "burps" every few seconds at high revs and secondly it is difficult to tune. The tuning screws still have their limiters on but I've tweaked the H screw up and down, then returned it to default - no difference.  It doesn't idle well - it either stalls or the chain moves too much, its very hard to find the sweet spot between these or it doesn't exist.

 

Could these issues be fixed by cleaning out the carburetor with carb cleaner?

[pleasant]

Difficult to tune, doesn't idle well- either stalls or chain moves too much. Indicates an air leak to me resulting in leaning of the mix, which can cause all those issue. Set it on idle- high idle if you can and get a can of brake cleaner or carb cleaner and gently spray around the flywheel area, clutch area and the carb area, but avoid spraying anywhere directly near the filter intake as it will give a false reading. If you have a leak then the engine will stall out or rev up independent of the throttle. When you spray near the area with the leak. Try that before stripping it down, as it can save a lot of hunting.

 

 

Edited October 13, 2022 by pleasant

[Muddy42]

16 minutes ago, pleasant said:

Difficult to tune, doesn't idle well- either stalls so chain moves too much. Indicates an air leak to me resulting in leaning of the mix, which can cause all those issue. Set it on idle- high idle if you can and get a can of brake cleaner or carb cleaner and gently spray around the flywheel area, clutch area and the carb area, but avoid spraying anywhere directly near the filter intake as it will give a false reading. If oyu have a leak then the engine will stall out or rev up independent of the throttle. When you spray near the area with the leak. Try that before stripping it down, as it can save a lot of hunting.

 

 

Thanks, I like that idea and will try it first.

[peatff]

135 don't have limiters, the one I have anyway and I had it from new. All they have is the splined adjuster screws. My friend has one as well and his has no limiters either. Warm the engine up then turn the L screw right in then out 1 1/4 turns, speed the tickover up to keep it running then adjust the L screw out till it starts to stall and run it back in a touch. I've had mine about 9 years now and it's been no trouble. Burping at high revs sounds like too much fuel 4 stroking it.

[adw]

The 135 has a governed ignition unit, so if you lean the mixture too much they do sound very strange at full revs when they hit the governor, I tend to screw the H jet in until they just hit the governor, then a further 10th of a turn and leave it, they can suffer with the impulse collapsing, this is part of an assembly screwed to the inlet side of the cylinder, they also do have ignition unit issues, I have replaced plenty.

[peatff]

13 hours ago, adw said:

I tend to screw the H jet in until they just hit the governor, then a further 10th of a turn and leave it,

 

Why run it lean ? I turn mine out till it 4 strokes but cleans up under load when cutting.

[pleasant]

2-stroke should 4-stroke to a degree when not under load, then like you say, clear their throats under load. That's why manufacturers state a bar and chain should always be fitted, or a head fitted to a brush cutter- all adds a degree of load when tuning.

[openspaceman]

16 hours ago, adw said:

The 135 has a governed ignition unit, so if you lean the mixture too much they do sound very strange at full revs when they hit the governor, I tend to screw the H jet in until they just hit the governor, then a further 10th of a turn and leave it, they can suffer with the impulse collapsing, this is part of an assembly screwed to the inlet side of the cylinder, they also do have ignition unit issues, I have replaced plenty.

 

2 hours ago, peatff said:

 

Why run it lean ? I turn mine out till it 4 strokes but cleans up under load when cutting.

He doesn't run it lean; by screwing in the HI needle the engine revs increase just to the point you can hear the limiter cutting in. Enriching the mixture 1/10 of a turn then causes the motor to start four stroking before the rev limit. This way the mixture will be right at full power a few thousand rpm below the rev limit or four stroking, just as you mention.

 

I find tuning rev limited things, like hedgecutters, quite difficult compared with chainsaws where the load can control revs more easily.

[Muddy42]

Thanks all. As described, adjusting the H screw doesnt make any difference, the saw still ‘burps’ on high revs with load.

 

 i will look for a leak with carb cleaner and reassess the situation.

[Muddy42]