562xp 550xp autotune question

[272super]

With the autotune on the 550xp and 562xp ,how will that change the issue of a lean mix or air leak causing a potential seizure? I have heard different things but if the saw has bad air leak or was run on straight gas, will it shut down before a seizure? Anyone know of one of these saws leaning from straight gas or air leak and scoring the cylinder or are they idiot proof? Thanks

 

[Str8six]

I don't think when strait gassed they run lean. Its the lack of lubricity that causes the seizure. I figure any air leak big enough to cause damage will be causing some other noticeable symptoms as well. Still need to have a little common sense. They can only dumb down things so much thankfully, we still got to use our heads.

 

[rob066]

From what I get is that when a major air leak happens, the saw richens to a point it will not run. No help for no oil though!

 

[MarkEagleUSA]

From what I get is that when a major air leak happens, the saw richens to a point it will not run. No help for no oil though!

It can only richen so much however. I remember reading somewhere (that I can't find now) that small air leaks are somewhat masked by AT to the point where the user may not know there's a problem. Major leaks probably will kill the saw if the user isn't paying attention.

And no help for no oil is very true. Even AutoTune can't fix stupid!

 

[Chris-PA]

You can't really idiot-proof anything because they're always developing better idiots.

Auto-Tune it pretty simple, no magic at all. It continually tests to see if the mixture is correct, and then adjusts to make it so by moving a valve in the main fuel jet (effectively it turns H needle). It has no idea if added air comes from an air leak or if someone just put on a new filter - if it is within the range to adjust it will. It is certainly possible for the system to know that it is at the limit of adjustment and it's still not right, and I would hope they have included such an out-of-range protection.

 

[KenJax Tree]

Idiot proof goes out the window as soon as you try to start it without reading the manual for the proper procedure.


Sent from my AutoTune carb

 

[MarkEagleUSA]

Auto-Tune it pretty simple, no magic at all. It continually tests to see if the mixture is correct, and then adjusts to make it so by moving a valve in the main fuel jet (effectively it turns H needle).

I may be wrong but I thought it's been said that all AT tests for is RPM, adding or removing fuel to maintain it at WOT. I guess technically that is the same as checking the mixture, but that's not what it's looking at.

 

[Chris-PA]

I may be wrong but I thought it's been said that all AT tests for is RPM, adding or removing fuel to maintain it at WOT. I guess technically that is the same as checking the mixture, but that's not what it's looking at.

The primary feedback system is to look at rpm, but it is not attempting to control the saw to a specific rpm or anything like that. What it does is to momentarily lean out the mixture every so often, and then it looks at the rpm to see what happens. Maybe a bit oversimplified, but if the saw speeds up then it was too rich, if it slows down it was too lean, etc. In reality I'm sure they're probably looking for a set small increase in rpm, but you get the idea. The reaction of the rpm to the "lean out test" tells the system where the mixture is. No input sensors are required, by looking at rpm under WOT conditions it is essentially looking mostly at the mixture.

 

[Str8six]

An air leak will cause one to run lean. Too much air and not enough fuel. Right?

 

[naturelover]

Not necessarily on an at or mt saw, as the carb will dump more fuel to it, possibly to the point of flooding it.

So is said.....


Sent from my iPhone 5 using Tapatalk

 

[MarkEagleUSA]

The primary feedback system is to look at rpm, but it is not attempting to control the saw to a specific rpm or anything like that. What it does is to momentarily lean out the mixture every so often, and then it looks at the rpm to see what happens. Maybe a bit oversimplified, but if the saw speeds up then it was too rich, if it slows down it was too lean, etc. In reality I'm sure they're probably looking for a set small increase in rpm, but you get the idea. The reaction of the rpm to the "lean out test" tells the system where the mixture is. No input sensors are required, by looking at rpm under WOT conditions it is essentially looking mostly at the mixture.

That certainly makes sense to this feeble old brain.

 

[hamish]

When the system does its lean out test every few seconds, upon recognizing a lean condition, it will dump more fuel into the system to correct the lean condition. For a user, you will notice higher rpm at idle (in most cases the rpm will raise to the point the clutch will engage, in massive air leak conditions you will be looking at max rpm at idle as the saw will feed more and more fuel trying to correct the condition.

AT Gen 1 systems are great, Gen 2 are even better, Gen 3 may cure cancer.

 

[SawTroll]

From what I get is that when a major air leak happens, the saw richens to a point it will not run. No help for no oil though!

Yes, the AT actually will save some top ends from lean seizure, but it save you from a streight gas or bad gas situation.