Why does my saw hate heat and humidity so much?

[Soundchasm]

You guys have talked me through many aspects of keeping my tiny little Husky 435 running, and I've used the crap out of it. When I first got it, it was IMPOSSIBLE to start with the factory settings. I got the carb adjustment tool and you guys got me going there.

Anyway, nice pleasant day and the saw starts, runs full out on 32" rounds all day just fine, idles, etc. Oppressive heat/humidity rolls in and it will die rolling off the throttle, and it wants to start on 1/2 choke. Temp/humidity goes down and I'm back in business.

Any thoughts? Thanks!

 

[Hasufel]

You guys have talked me through many aspects of keeping my tiny little Husky 435 running, and I've used the crap out of it. When I first got it, it was IMPOSSIBLE to start with the factory settings. I got the carb adjustment tool and you guys got me going there.

Anyway, nice pleasant day and the saw starts, runs full out on 32" rounds all day just fine, idles, etc. Oppressive heat/humidity rolls in and it will die rolling off the throttle, and it wants to start on 1/2 choke. Temp/humidity goes down and I'm back in business.

Any thoughts? Thanks!

I'm not an engine guy but maybe that's nature's way of telling you that summer is for beer and fishing?

 

[peakbagger]

Are you readjusting the carburetor for the change in weather conditions? As my old saw got older it was fare more intolerant of weather conditions.

 

[WoodyIsGoody]

I'm not an engine guy but maybe that's nature's way of telling you that summer is for beer and fishing?

I think it's his saw telling him to move to the Pacific Northwest!

But beer is a year round endeavor, I never slack off just because it's nice and cool!

 

[Soundchasm]

Are you readjusting the carburetor for the change in weather conditions? As my old saw got older it was fare more intolerant of weather conditions.

Well, I apparently nailed it for a 70 degree day! As a guitar player, I'm engine-ignorant, but after the reports of the grounded planes due to the heat, I started thinking that these air-breathers have their preferences, too.

I don't have any insight if higher temps/humidity mean thinner/thicker air, leaner or richer, for better or worse, high side or low side, till death do us part.

 

[Soundchasm]

I think it's his saw telling him to move to the Pacific Northwest!

But beer is a year round endeavor, I never slack off just because it's nice and cool!

Man, I had a cup of coffee in Seattle once and I never got over it!! BEAUTIFUL state.

 

[Soundchasm]

Found some stuff. Looks like saws need to be leaned out in heat and humidity. But high side, low side, or both?

http://www.arboristsite.com/community/threads/high-humidity-carb-problems.107017/

Also-

Air temperature-When the air temperature increases, the air density becomes lower. This will make
the air-fuel mixture richer. You must select jet sizes with a lower number to compensate for the
lower air density. When the barometric pressure decreases, the opposite effect occurs.
Humidity-When the percentage of humidity in the air increases, the engine draws in a lower
percentage of oxygen during each revolution because the water molecules (humidity) take the
place of oxygen molecules in a given volume of air. High humidity will make the air-fuel mixture
richer, so you should change to smaller jets.

 

[WoodyIsGoody]

Found some stuff. Looks like saws need to be leaned out in heat and humidity. But high side, low side, or both?

Air density changes will affect all circuits. Assuming it was properly tuned for higher density conditions, you would want to lean both H & L circuits. Most people tune their saws by ear but the range of adjustment on modern saws is so small it can only compensate for normal atmospheric variation, not worn or gummed up carb parts. You can also burn up the motor if you do it wrong or forget to re-tune when the air density increases.

Or you could get a smart saw. Always tuned optimally without mucking with H& L circuits. The range of adjustment on the auto tune saws is much larger compared to the H&L screws.

 

[Soundchasm]

I'll probably try giving both screws a 1/4 turn counter-clockwise as soon as I have the misfortune of working on a perfectly good "beer day".

I did a bunch of maintenance on the saw last year, learning as I went (saw's lucky to have survived). I don't know why, but in today's throwaway world, I get a lot of satisfaction out of keeping things running that by all rights, ought to be dead. I have nothing but respect for those with mechanical aptitude. Quite jealous, in fact.

 

[sen166]

If this is happening when it is hot out, you could be experiencing "vapor lock". Happens to me all of the time in summer during high heat periods when running the weed whacker or chainsaw.

 

[Soundchasm]

If this is happening when it is hot out, you could be experiencing "vapor lock". Happens to me all of the time in summer during high heat periods when running the weed whacker or chainsaw.

Wow! That is so entirely plausible. Carb adjustment won't help with that... I just read up on vapor lock and that reminded me of a funny story.

Back around '90 I moved to Dayton. Dad had a one ton Ford box van I borrowed for the move. Whenever it was, I remember it being so hot I thought I was really going to injure my friends who were helping.

Went to drive from Dayton to Muncie and the heat was insane. Empty truck would lose power going up any incline. I couldn't keep to speed even at 3% inclines. I finally decide I have to get off the road and try to figure out what's happening.

So I pull off at a rest stop and go to the "truck" side. I pull in behind an IDENTICAL Ford box van. He's got the same damn thing going on!! His box van is a Kawasaki Race Team truck for a motorcycle team. Since he's considerably smarter than me, he shows me how to pop open the cowl in the center of the cab and shows me the gas line running right over the top of everything soaking up all that heat.

So anyway, I leave the cowl loose, roll down the windows, turn the heat up full blast, and drive the last hour home!! That was one hot son of a gun!!

 

[Dobish]

i was noticing this yesterday on my husky as well. i didn't think I was going to be out there cutting through as much as I did, but I noticed I was going through a lot more gas, and it was bogging down where it normally didn't do that. By the time I remembered to adjust the carb, i was tired of being vibrated, and decided to load up the wood into the truck and start making piles!

Another reason i don't like cutting in the summer.

 

[Ashful]

If this is happening when it is hot out, you could be experiencing "vapor lock". Happens to me all of the time in summer during high heat periods when running the weed whacker or chainsaw.

This is what I was thinking. First, make sure you don't have the "winter" air shutter closed, which pre-warms all intake air thru the cooling fins. It's located behind the air cleaner on older Stihls. Second, make sure you're not running winter gas, which typically has a lower boiling point, always problematic for older saws in warm weather. Third, make sure you blow your saw out with compressed air, so that it's getting maximum clean air flow.

 

[Soundchasm]

This is what I was thinking. First, make sure you don't have the "winter" air shutter closed, which pre-warms all intake air thru the cooling fins. It's located behind the air cleaner on older Stihls. Second, make sure you're not running winter gas, which typically has a lower boiling point, always problematic for older saws in warm weather. Third, make sure you blow your saw out with compressed air, so that it's getting maximum clean air flow.

Thank you for good advice. I'm running summer blend 92 octane at 40:1, though the Husky is 50:1. I did check the filter quite recently and it appeared to be clean, far different from the first time a buddy pointed out, "Hey, did you know you have an air filter?"...

I've got one other issue to address, and it may play into things a little here, but the spark plug wire has a gouge where the cover presses it against the cylinder. I've "re-insulated" it since I discovered I could stop the engine by pressing the wire against the cylinder. I'd have to think that once things got piping hot in there that the integrity of the previous patch would get dodgy. We'll see if the new patch makes any difference.

If I fiddle with that wire I'll make a new thread.

 

[jetsam]

Check to see if any fuel lines are routed to bad places where they get too hot, too- that can cause vapor lock all by itself.

If you are losing coil current to the block, that could cause issues. Fix or replace the wire where it's frayed. Black tape is usually vinyl, so it's not good for high heat applications.

I would also say just tune the carb every day the first time you use the saw. Juat like tuning your guitar, it will be a 30 minute Thing the first time, but it will be a 2 minute thing once you are used to it, and you'll be glad you did.

 

[Soundchasm]

Check to see if any fuel lines are routed to bad places where they get too hot, too- that can cause vapor lock all by itself.

If you are losing coil current to the block, that could cause issues. Fix or replace the wire where it's frayed. Black tape is usually vinyl, so it's not good for high heat applications.

I would also say just tune the carb every day the first time you use the saw. Juat like tuning your guitar, it will be a 30 minute Thing the first time, but it will be a 2 minute thing once you are used to it, and you'll be glad you did.

I've re-done the fix to the wire. I cut heat shrink tubing lengthwise to cover the gash, and then used cloth gaffer's tape around that. So the heatshrink ought to provide high temp electrical integrity.

Boy, I've had days where it DID take me 30 minutes to tune a guitar!! And you talk about sensitive, the minute the temp or humidity changes, those strings go wherever they want. I could write a treatise on tuning strategies, from machine heads, to CAD/CAM finished frets, body heat, strobe tuners, finger pressure, string gauge, pick pressure, stable neck wood and truss rods, compensated nuts, bone nuts, roller nuts, floating tremelo, hard tails, capos, and on... But it is a beautiful thing to flog one for 70 minutes and have it stay put.

Larry Carlton told a joke where he said if you've been playing for 40 years, you've spent 20 tuning.

I'll pull my carb notes out and give it a shot. And I had another thought - does the 40:1 gas mix make any difference? Just adjust the carbs for the fuel being run?

 

[Ashful]

And I had another thought - does the 40:1 gas mix make any difference? Just adjust the carbs for the fuel being run?

Yes, it does, but the diff between 40:1 and 50:1 is not as drastic as what we were dealing with a generation ago (ie 16:1 and 32:1).

 

[jetsam]

I've re-done the fix to the wire. I cut heat shrink tubing lengthwise to cover the gash, and then used cloth gaffer's tape around that. So the heatshrink ought to provide high temp electrical integrity.

Boy, I've had days where it DID take me 30 minutes to tune a guitar!! And you talk about sensitive, the minute the temp or humidity changes, those strings go wherever they want. I could write a treatise on tuning strategies, from machine heads, to CAD/CAM finished frets, body heat, strobe tuners, finger pressure, string gauge, pick pressure, stable neck wood and truss rods, compensated nuts, bone nuts, roller nuts, floating tremelo, hard tails, capos, and on... But it is a beautiful thing to flog one for 70 minutes and have it stay put.

Larry Carlton told a joke where he said if you've been playing for 40 years, you've spent 20 tuning.

I'll pull my carb notes out and give it a shot. And I had another thought - does the 40:1 gas mix make any difference? Just adjust the carbs for the fuel being run?

I play mostly 12 string, so I've spent 30 years tuning. I did find that just permanently tuning it a half-step down (in any tuning) really helps with temperature variations. Probably get some extra years out of the neck, too. Haven't tried it on any of my sixes (one stays in tune anyway, and the other one's intonation is so bad that tuning is a series of estimates and compromises anyway...)

Think of your saw like a guitar, though. It's got a bunch of variables going, and it is not exactly the same as every other saw. Tune it regularly and it will start to tell you when it needs to be tuned, and when you can skip it. Some saws will just cut all year, some are fussy old ladies that need more attention, and some are broken and need surgery.

 

[Soundchasm]

I play mostly 12 string, so I've spent 30 years tuning. I did find that just permanently tuning it a half-step down (in any tuning) really helps with temperature variations. Probably get some extra years out of the neck, too. Haven't tried it on any of my sixes (one stays in tune anyway, and the other one's intonation is so bad that tuning is a series of estimates and compromises anyway...)

Think of your saw like a guitar, though. It's got a bunch of variables going, and it is not exactly the same as every other saw. Tune it regularly and it will start to tell you when it needs to be tuned, and when you can skip it. Some saws will just cut all year, some are fussy old ladies that need more attention, and some are broken and need surgery.

I like your thinking there. I remember my Dad asking me (honestly) why I needed more than one guitar. He had horses so I asked him if a Morgan was the same as a Saddlebred was the same as an Arabian, etc., and the lightbulb went off for him. He's admired every one I've ever gotten since.

I'll send you a PM concerning a lifesaving guitar operation done with a Plek machine. The results Blew My Mind.

I'll get out my tuning notes and give it a shot. Every machine is an individual and deserves to be treated as such.