Check and KNOW your Altitude

I have my gps in the truck set to show current elevation. It's surprising how much it varies around here. My house is at 343'... I can be at the ocean in about 3 miles and there aren't any noticeable hills..

 

A change in temp of 30 degrees will make a difference as will a 1000' change in altitude. The thing is that both temp and altitude are at work here. Here is more than you ever wanted to know about all three factors. http://www.ask.com/wiki/Density_altitude

 

My super power full, trusty, light saber Earthquake 3814, which is my work truck saw was tuned this winter. This summer in the high 90s it would blog up off idle and load up and cut off at idle...acted rich on the L screw. I never got around to retuneing it but the other day at 80F the problem was not noticeable.

My best guess was it was in the 40-55f range when I tuned or tested it and was running fine.

 

You've done a great job of explaining the effects of air density on saws. Ultralight aircraft use mostly 2 stroke engines and are affected the same way of course. Way too many engine outs have happened because pilots let their engines get too lean. Keeping track of chainsaw engines regarding altitude and/or temperature is plenty... imagine adding airspeed effects on a prop, speeding up or loading down engine speeds. S'nuff to give a guy a headache... ...

 

I would imagine an airplane is tuned to max rpm's as that prop ought to put a pretty goodload on the engine.

Like a ttrimmer...tune it to max rpm.

No idea really just guessing I am not a pilot and dont know anything about them.

 

You're right... the engines, gear drives and propeller are all matched so max engine RPM happens at about the same speed as the prop has it's best thrust (in a perfect set-up).

 

Worse yet is trying to take off from a hot and high place, aircraft are at a disadvantage in these circumstances add to that the impact of humidity and you have a formula for disaster. I'm not a pilot, my father was a US Navy Aviator for 30 years and some of it has rubbed off.

Like Clemsonfor noticed; when any or all the factors are at work, you WILL notice a change in how your saw runs, and your tune is the FIRST place you should look for a solution!

 

As one who did not grow up around chain saws or ever have reason to use one regularly, I found it surprisingly challenging to learn to tune by ear, and to recognize when the saw was or wasn't running properly. I found the oft-linked sound recordings at Madsen's to be no help at all. I read forum posts about tuning... four stroking -- what is that? Cleaning up in the wood -- huh? It clicked for me a few months ago and now it seems obvious, but I know it isn't. Just a couple of days ago I bought a saw (044, woot!) from a guy who'd inherited it in 1997. It ran great, he said. When I tried, it did start on the first pull, but man, it was way too rich, sluggish response and low RPM. All he'd noticed, though, was that it reliably started and had never needed repair. The carb screws were packed with so much sawdust that it was impossible to get a screwdriver into any of them. I don't think he had any idea what the saw was really capable of. I wish I could come up with something to say to people who don't yet get it, that would do more than just cover my own butt.

 

And then you bring in limited coils...thats a huge monkey wrench into tuning...that sounds like four stroking???

 

Yeah they make it even trickier to tune saws like the 7900.

 

Muffles things a bit, does it?

 

And bogs it up

 

I know it isnt altitude related, but when I tune any saw that goes out after repair, I allways remember to use pump gas with ethanol. If I use the non-ethanol fuel and tune ....... its only a matter of time before its toast ......... (non autotune)

 

I guess e gas would make it run hot cause of the higher temps

 

You need more high jet due to the alcohol. You need about 2.2 times the fuel volume for alcohol compared with gasoline.

If you tune with non ethanol gas then run 10%, you will run lean and waste a P&C

 

When in doubt, one full turn out on each the L and H screws, they will always be really close. Inform the customer that it will need to be fine tuned. I ship modded saws all over the country and this has been my insurance.