Strange "Tuning" Issue Solved

[lefturnfreek]

Nice saw, needs more piss revin'

 

[Chris-PA]

Nice saw, needs more piss revin'

No piss revin' for now, the damn thing broke another rear A/V spring today. I swear it's the most unreliable saw I ever used - it's possessed.

 

[Kostas]

You replace the rear spring often?Mine broke a couple of days ago but after 4 years of abuse.Can't call it unreliable imo.In your video,i think the saw needs a little ccw on the low screw,it sounds wierd and it takes too long to come from high rpm's to idle.

 

[Chris-PA]

You replace the rear spring often?Mine broke a couple of days ago but after 4 years of abuse.Can't call it unreliable imo.In your video,i think the saw needs a little ccw on the low screw,it sounds wierd and it takes too long to come from high rpm's to idle.

Yes, I've put a couple of those on, and that's the one that broke again. The 20" bar is too much force for the springs I suspect.

I didn't have the tuning quite right in that video as it was the first I'd ran it with the bored out carb since it had proper spark. Although the biggest issue was that the idle was set too high since I'd forgotten to bring the right screwdriver to the woods.

 

[Kostas]

Yes, I've put a couple of those on, and that's the one that broke again. The 20" bar is too much force for the springs I suspect.

I didn't have the tuning quite right in that video as it was the first I'd ran it with the bored out carb since it had proper spark. Although the biggest issue was that the idle was set too high since I'd forgotten to bring the right screwdriver to the woods.

You are right,20"" bar put a lot of stress on the rear spring.I run a 18"" on mine,it's more suitable for the saw.

 

[lefturnfreek]

No piss revin' for now, the damn thing broke another rear A/V spring today. I swear it's the most unreliable saw I ever used - it's possessed.

Ha ha you should take my mini Mac's as they so enjoy a shop bench vacation for most of the year...love em when they run...but FLOG..keep running....

 

[heyduke]

The cylinder on mine is plated too. The biggest problem with these saws is the vibration from the engine. My guess is that when they enlarged it to 46cc the counterweights were not large enough for the increased mass of the piston. The A/V masks it (and is in turn weak), but the vibrations rip the saw apart, especially with the poor choice of fasteners and lack of locking hardware.

The tuning on mine was always pretty consistent which is why this recent change was noticeable. However, one requirement with these saws is to add some sort of damper/support under the air filter mount, which was not provided on the early saws. The later ones had a rubber blister that sat under the filter mount, but they deteriorate and they are not attached so they are easily lost if the carb is ever removed. Without it the carb will resonate like mad at various rpms, which is detrimental to maintaining mixture control. The similar Husqvarna 136/137/141/142 has a metal mounting bracket at the front edge of the carb.

The other problem that can effect tuning is the stupid intake boot & plate design. The rubber boot deforms at the end where the impulse channel is formed, and the plate has slots that are not needed. The impulse can become connected to the intake.

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Mine has been redesigned:
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chris- i like what you did with the carb to boot connection, but i have a modest proposal. from the days in my youth when i used to scratch asphalt with my motorcycle's foot pegs, i used to add a bit of lead to the mirror rear-view housings to lower their resonant frequencies and enable using the mirrors at speed. as built they would vibrate so badly that they were useless. so, i was thinking that if you used a thin sheet of lead instead of al between carb and boot, you might be able to eliminate resonant vibrations at operating rpms, or maybe a fishing weight on the filter assembly.

 

[Chris-PA]

You are right,20"" bar put a lot of stress on the rear spring.I run a 18"" on mine,it's more suitable for the saw.

Understood, but the thing I like this saw for is that it's so light yet pulls a 20" bar well enough - it makes a nice felling saw for stuff of appropriate size. I have plenty of other saws with 18" bars, some even lighter. I'm thinking about how I might give it some additional support.

chris- i like what you did with the carb to boot connection, but i have a modest proposal. from the days in my youth when i used to scratch asphalt with my motorcycle's foot pegs, i used to add a bit of lead to the mirror rear-view housings to lower their resonant frequencies and enable using the mirrors at speed. as built they would vibrate so badly that they were useless. so, i was thinking that if you used a thin sheet of lead instead of al between carb and boot, you might be able to eliminate resonant vibrations at operating rpms, or maybe a fishing weight on the filter assembly.

Changing the mass is certainly a good way to address a resonant vibration, but in this case the fundamental problem is that the carb is cantilevered on a mount that is quite flexible. In fact the mount is cantilevered too, attached by two screws at the base. The top of the mount is supposed to be reinforced by the top cover pressing on the rubber partition gasket, but it doesn't work because that gasket always comes off and it wears terribly anyway.

They knew there was a problem because on the Husqvarna 142, which was part of the same design project and uses similar engines, they added a metal bracket to the front of the carb, and on later versions of this saw they used a cheap rubber piece shoved under the filter. I'm using a piece of fuel line cut to length which works and holds up much better than the thing they used.