Kick myself in the butt! 371XP smoked

[scootr]

Here we go. My buddy says, hey there is a big old Oak that fell down off the Hwy up here, let's go get it. Okay, throw the 371XP in his truck, and we are off. The Oak was big, prolly 40-46" dia., I fire up my saw, running like a mad dog. Chips are flyin, the saw is just screamin (unlimited coil)He is impressed. My saw is runnin better than it ever had.

Then, my buddy says, the barks burnin. HUGH? I shut her down, sure enough, smokin bark. I'm thinkin, this is not good. Well, that place on the Hwy was about 2500', I usually cut at about 5000". I should have checked carb settings, I didn't. Smoked the piston, sheet! It was getting late, we were in a hurry.

Carry that carb screwdriver with ya, and check your settings when changing elevations. Another lesson learnt the hard way. Dangit.

 

[wigglesworth]

That sux. Hopefully just a piston and not a cylinder. I find myself checking for 4 stroke constantly. It's became a good habit to have.

 

[logging22]

:jawdrop: That sux!

 

[Evan]

my guess is it was already running lean at 5000

 

[parrisw]

Would 2500' make that much difference?

 

[scootr]

It was runnin great last time at 5000". Today was much cooler and lower elevation. I think I'll check seals while I have it down. Never had a prob with this saw.

HMMMM, think i'll check everything! Something bad happened.
I never saw a saw saw, like this saw saws. :jawdrop:

 

[056kid]

I dont think 2500 feet is going to burn up a saw, especially in cool weather.


Perhaps a tad lean to begin with..

Did you look in the ports to see that it wasa toast?

 

[mtngun]

Would 2500' make that much difference?

Yes.

 

[ol'homey]

Many things can cause a saw to go lean:
drop in ambient temp since the last time saw was used
saw tuned to 4 stroke in the shop under no load, then goes lean under load when it gets hot
bad fuel pump diaphragm flappers that can't pump enough fuel to keep up in a long cut but seem fine when blipping the throttle
plugged fuel tank vent
air leaks etc.

So what can you do to ensure none of these problems bite you in the butt?
I constantly check for 4 stroking. I fire the saw up and let it idle (if it won't idle when cold it's not right) for a min or so. Then I'll hold it at WOT for a sec or 2. I'm looking for oil flying off the bar and I'm listening for a good 4 stroke burble. If I don't hear the burble and see the oil I stop and fix the problem or pick up another saw. Before I put the bar in the wood the saw is burbling at WOT. When I put the bar in the wood I want to hear the transition from 4 stroking to the normal 2 stroke whine. If I'm in the middle of a long cut I'll lift up a little to unload the saw. I want to hear the transition back to the burble, then I'll let it go back to eating, kinda like burping the saw. I hold it at WOT all the way through the cut, and I want to hear the burble when the cut is finished. The burble upon exiting the cut does a couple things. The unburned fuel in the cylinder which causes the burble also cools down the cylinder preventing scuffing, scoring and other bad things that happen when a saw gets too hot. The burble also tells me that the fuel system is functioning properly to provide enough fuel to keep that cylinder happy under full load and heat.
I realize that I'm in the minority here holding the saw at WOT for a sec or so before the cut, through the cut, and for a sec or so AFTER the cut. IMO the saw is under less stress burbling at WOT, no load, with the flywheel fan at max rpm blowing cool air over the cylinder than it is loaded in the cut. Most folks are scared the WOT rpms are gonna hurt the saw. I've seen guys back off the throttle near the end of the cut and let the saw lug through the last part of the cut because they didn't want to over rev it. The saws already hot from a long cut and now they are lugging it at part throttle. IMO if the saw has a good solid burble at WOT the rpms aren't going to go high enough to hurt it. I've never seized or burned up a saw or thrown a rod etc. I do know folks that have burned up saws due to being lean. I ask why didn't you check for 4 stroking? Well I blipped it a couple times, thought I heard it 4 stroke, so I figured it was good, didn't want to hold it too long at WOT and have it blow up. Well it blew up anyway didn't it, cuz it was lean and you didn't know it because you were afraid of WOT when you should have been scared of LEAN!
Lean is what kills saws, not 4 stroking at WOT. Remember if she ain't strokin', she ain't right!

 

[LarryTheCableGuy]

Yes.

+1, that plus the cooler temperatures could be enough.


.

 

[GASoline71]

Hmm... I have cut for years with saws tuned in the lowlands, and run in the mountains for years... no probs.

Gary

 

[superfire]

weird

sounds weird to me. i want to see picts of the slug to see what is going on i wonder if your 2 stroke fuel mix could have been bad. i have stihl pro saw an run it at 1000 feet and up to 6000 foot in elevation and never have had to adjust the carb. sounds bad any way you look at it

 

[056kid]

There is no wayyy that a 4 stroking saw with no load is going to lean out in the cut unless it wasent tuned properly to begin with...

 

[AUSSIE1]

Yeah, sounds like a lean saw running leaner.

Bugger, might have to fit a big bore kit with some tweaking!

 

[ol'homey]

Tuning at say sea level and then going into the mountains would tend to make it run rich. Higher altitude=less oxygen. What scootr did was the opposite, he tuned at 5000' and then went to 2500' which would tend to make it go lean. One thing I don't understand yet is what does smoking bark have to do with a burnt piston? I'm thinking dull chain caused the smoking bark. Maybe scootr is trying to say the dull chain made the saw take forever to get through the cut, which allowed the saw to overheat due to the lean condition at WOT, which burnt up the piston?

 

[TraditionalTool]

Hmm... I have cut for years with saws tuned in the lowlands, and run in the mountains for years... no probs.

Gary

Yeah, but don't you use Gary Goo? I thought that stuff was known to handle the widest variety of ambient temperature change, more so than any lubricant.

 

[super3]

I constantly check for 4 stroking. I fire the saw up and let it idle (if it won't idle when cold it's not right) for a min or so. Then I'll hold it at WOT for a sec or 2. I'm looking for oil flying off the bar and I'm listening for a good 4 stroke burble. If I don't hear the burble and see the oil I stop and fix the problem or pick up another saw. Before I put the bar in the wood the saw is burbling at WOT. When I put the bar in the wood I want to hear the transition from 4 stroking to the normal 2 stroke whine. If I'm in the middle of a long cut I'll lift up a little to unload the saw. I want to hear the transition back to the burble, then I'll let it go back to eating, kinda like burping the saw. I hold it at WOT all the way through the cut, and I want to hear the burble when the cut is finished. The burble upon exiting the cut does a couple things. The unburned fuel in the cylinder which causes the burble also cools down the cylinder preventing scuffing, scoring and other bad things that happen when a saw gets too hot. The burble also tells me that the fuel system is functioning properly to provide enough fuel to keep that cylinder happy under full load and heat.
I realize that I'm in the minority here holding the saw at WOT for a sec or so before the cut, through the cut, and for a sec or so AFTER the cut.

You do this for every cut?

 

[bitzer]

You do this for every cut?

I could see doing that for the first long cut of the day to make sure your saw is running correctly according to weather and elevation. After that it would be good for the day I would think. I always keep my carb screwdriver handy and check 4-stroke when starting a day if a saws been sitting for a while or the weather was different the last time I ran it.

That really sucks burning a piston like that! I wonder if the muffler ports face the wood and the excessive lean heat was torching it?

 

[Streblerm]

Some of my cutting buddies make fun of me

I never go anywhere without my carb screwdriver. I like to hear a little burble in the cut every once in a while. I probably tweak the carb screws almost every time I start cutting. There's a sound I like and it keeps my plug a slightly dark tan. I know I could go leaner... If it isn't making that sound, you gotta tweak the screws. You must become one with your saw. Singing is good, screaming is bad.

Some of my friends have come around after I give their saws a little tweak, some of them still poke fun.

I don't know what it is about old equipment, it seems like they can almost always benefit from a little carb tickling. I don't know if it's fuel quality, environment, or what.

Maybe it isn't just old equipment either, seems manufacturers are going to some degree of compensating carbs or fuel injection on everything


The art of carburetor tuning

 

[mtngun]

Hmm... I have cut for years with saws tuned in the lowlands, and run in the mountains for years... no probs.Gary

Tuned in the lowlands, it will run RICH in the mountains. That's why you've had no problems.

Tuned in the mountains, it will run LEAN in the lowlands.