How does Auto tune work?

[CJM]

what is the price for a 576xp autotune carb just out of interest ?

 

Husqvarna 576XP Chainsaw (2011) Parts Diagram, Carburetor Details

[CJM]

This is all I can find for the auto bit of the carb

 

Husqvarna 576 XP Auto Tune (2009-02) Parts Diagrams for Carb. Parts

[spudulike]

That's one part of the whole system I can't understand, how does it control the timing, the timing is fixed point (ie, the magnets). This produces a pulse, unlike the old points ignition, which charged a capacitor and created a short circuit as its timing. After all, why bother with a key on the flywheel?

QUOTE]

 

I thought from your posts there wasn't much that escaped your knowledge Eddie:lol:

 

On non autotune modern saws, the flywheel is keyed as the coil has a set advance/retard curve and isn't clever enough to automatically register where it is firing in regards to the position of the piston/crank. all it does is set the advance depending on the speed of the saw in a set position in regards to the position of the coil and flywheel.

 

A non fixed flywheel would cause a spark all over the place hence the backfire when the spark is retarded past TDC when the key goes!

 

Some saws have the coil align with the magnets at TDC, some align at around 20-30 deg in advance - on the KM55 I am working on, it is around 30 deg retarded which is very unusual. This is just the design of the engine. 024/026 - bang on TDC, 066/357/346/all well in advance of TDC, just depends on the coil/saw.

 

The coils on modern machines, retard the ignition at low revs to circa 5 deg advance, bring it up to around 27 - 30 deg at peak power and then drop it back to 20-25 at WOT. This is electronically set, the advance curve can't be changed and it HAS to work with the specific design of the saw otherwise the advance will be out of sync with the crank/piston.

 

If the coil to magnet position is set to TDC then the coil must produce the spark at some 330 degrees on from passing the magnet at peak speed - that is the only way it can work - put a timing light on a saw and you will see PDQ if the coil is advancing or not!

 

Old saws had set advance to around 25deg, this was enough not to break your arm at start up but enough to get some decent power out of them. Newer coils had changed advance to make starting easier and to get nearer the 30 degree mark for maximum power and retardation at higher revs to stop detonation.

 

Auto tune - I don't know if the ignition curve is being controlled by the autotune, some say it is and logically it makes sense to so max torque can be pulled out of the machine for any given situation. Some say it is but have no specific evidence of it.

If it is isn't automatically controlled, there will be a built in curve as explained above!

[peatff]

I know the 540xp is under £70 but as in 2 parts one of which won't go wrong.

 

Sent from my iPad using Arbtalk mobile app

 

To quote Douglas Adams "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

 

According to the post about the timing being controlled by magnets this says the autotune does not alter it it just reads it and alters the mixture accordingly. I personally have no problem with auto and do not wish to alter it in any way whatsoever adw and am just curious how it works and am convinced that someone will want to fiddle with it, that's just human nature like porting standard saws. If someone can get an extra .5 hp by adding a resistor or something as opposed to dismantling and grinding ports and drilling silencers and they have the ability to do it then they will probably go ahead and do it, like fitting a Power Commander on a Hayabusa, do you really need more power ? Probably not but men are just boys with more money.

[spudulike]

To quote Douglas Adams "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair."

 

According to the post about the timing being controlled by magnets this says the autotune does not alter it it just reads it and alters the mixture accordingly. I personally have no problem with auto and do not wish to alter it in any way whatsoever adw and am just curious how it works and am convinced that someone will want to fiddle with it, that's just human nature like porting standard saws. If someone can get an extra .5 hp by adding a resistor or something as opposed to dismantling and grinding ports and drilling silencers and they have the ability to do it then they will probably go ahead and do it, like fitting a Power Commander on a Hayabusa, do you really need more power ? Probably not but men are just boys with more money.

 

Like my signature below says................

[adw]

576 Carb complete with auto tune unit £114 auto tune nit on its own £73

[spudulike]

Are these prices inclusive of VAT end user prices?? doesn't seem too bad value.

 

Just waiting for the day I get a buggered unit in so I can se if there is any way of stripping/repairing these units!

[adw]

Sorry plus vat, less good customer discount maybe!

[spudulike]

Sorry plus vat, less good customer discount maybe!

 

Cheers:thumbup:

[traktorz]

Electronic circuits needs power supply, both generated and stored. On a chainsaw, the needed power is magneto generated, rectified, stabilized and I suppose, stored in some kind of ackumulator.

 

Does this affect the starting behavior of a M-Tronic/AutoTune versus a traditionally equipped carburetor saw? Do these need some extra pull at start?