Check and KNOW your Altitude

When buying or selling saws coming from or going to outside your local location it it always good to know/advise your buyer or yourself the altitude above sea level for both locations, so that you know to tune the saw. When I ship out a saw, I check the receiving location altitude and advise the buyer that they must tune for their location. Rochesrter NY is 550 feet above at the airport but in my location it is only 246 feet above sea level. So I know that if I ship a saw to WY the buyer MUST retune for the 6100 ft above at their location and always advise them to retune!

Here is a place you can go to get altitudes of most major cities in the USA.
http://www.altimeters.net/cityaltitudes.html

Also saves you a lot of wasted time when the new owner gets the saw and sends you one of those "I got the saw today and it doesn't run for chit" or "I ran the saw for not even a tank and it blew up or stuck the piston" messages! The further above your location the saw goes it will go way rich Fuel/Air the further below your location the saw will go lean Fuel/air. The first condition results in the 'doesn't run for chit' comment the second condition if extreme enough will damage the saw. I also advise buyers to take the saw to a local dealer if they are not confident in their tuning abilities.

 

This is a great idea!

 

I used to know, but now I forget (isn't this a politician's defense when caught doing something wrong?).......... will a saw coming from low elevation to a higher one need leaned or richened?

 

Reading his post it sounds like it would need to be leaned as it would be rich.

Just rephrashing what KRL said.

 

As the altitude increases the Air gets less dense resulting in a lower proportion of Air mixed with the Fuel at combustion time causing the engine to go rich, so one must reduce the amount of Fuel mixed with Air. As altitude drops the Air becomes more dense, a higher proportion of Air mixed with Fuel at combustion time causing the engine to shift towards a lean operating condition. This is the dangerous one. It is the one that results in 'the saw blew up' comment. In this condition one must increase the amount of Fuel mixed with Air at combustion time.

 

Yep.

Good post Tim.

 

What if you just opened both screws super fat before sending off and advise the saw must be tuned at arrival.

 

So for example, Randy is at 1,719 ft. in TN and I am at 997ft in Ohio....... so I'd need to richen a little (assuming Randy sends the saw optimally tuned for his location).

 

Yeah that does happen. I've cut at 3400 ft and then down lower and seen a big increase in rpms.

 

Yes Bryan, you would need to richen a little. Randy probably does the same as I do; tune for optimal performance at MY location then set back to factory or to a 'safe' setting. Otherwise you cannot be sure the saw runs correctly anywhere.

I have tried that, set it for my location to make sure it runs right when I test it, and then set it back to factory starting specs, on a 372 1 & 1. However some folks get confused because there are two Rich/Lean ratios you are dealing with; Oil/Gas and Fuel/Air. So, I tell them to run 32:1 H1R to gas. Carb settings have nothing to do with Oil/Gas, the H/L screws have to do with Fuel/Air.

 

Is this a good argument for EFI?

 

Yes, but present day a great argument for Autotune/ M-tronic or knowing how to tune a carb (and having a proper tiny screwdriver handy!)

 

Any idea how large a change in elevation it takes to make a noticeable difference?

 

1k ft. can make a difference of good to too lean.

 

Million and two different calculators Google it.

Any change WILL make a difference, the larger the change in altitude the bigger the difference. It seems your are asking the lazy man's question; when do I REALLY have to wory about this stuff. Would you worry less if they found 1 cancer cell instead of a million.

Joking aside, Mike is right 1000' can make that big of a difference. Now to further complicate matters, air temp also makes a difference in that cool air is more dense than warm air. Which means at a given altitude if the temprature is higher than when you last tuned your saw your saw will be rich fuel/air, conversely if the temp is cooler your saw will become lean fuel/air. Keep your tuning tools in your cutting kit!

 

I think its a good question...... So call me lazy.

Take for instance I start cutting in the heat of the day at the top of a ridge and everything is tuned great and I finish in the valley at dusk. Will the change in tune be enough to matter?

 

Not that so much as wondering when to be emphatic about it.

 

Any saw I sell I tune fat... Like a couple thousand rpm below max spec. If I tune to max spec then there isn't much room for error when someone fiddles with the carb screws.