Limited coils and cat mufflers

[srb08]

Can someone explain the reason some saws have rev limiting coils and others not and why some saws have cat mufflers while others don't?
I assume that it's EPA driven but I don't understand the applications and why it's only on certain saws and brands and not on others.

 

[chadihman]

Ummmmmmmmmmmmmmmmmmmmmmmmmmmmm thats a good question.

 

[LegDeLimber]

The real knowledge is in the hands of the guys who are active in these saws.
I'm only throwing some conjecture,
but it seems the non cat mufflers are likely to be on the strato engines (EPA thing)
Limited ignitions?
I'm guessing a product "durability" warranty issue, primarily
and I expect it could be intended to keep the loading, thus temps of a catalyst under control.

also, maybe keeps some chain speed/ other moving parts liability issues under some legal threshold.

 

[Chris-PA]

I believe limited coils are just to prevent the saw from overreving.

When faced with emissions regulations some companies invested in serious R&D to develop things like strato engines (i.e. companies with smaller market share like RedMax) that make a real improvement in efficiency and emissions.

Other companies just slapped on some limiter caps or special mixture screws and packed some catalyst material in the mufflers - this on a 2-stroke engine that by nature pumps unburned fuel out the exhaust, equipped with a carb that is incapable of holding a fixed fuel/air mixture with varying airflow (load). The concept is to tune it as lean as you can get away with and let the cat deal with all the unburned fuel it will put out anyway.

Since 4-stroking is just the engine misfiring from <i>way</i> too much fuel (a characteristic of the carbs), that's not going to work well. And since loading the engine will make it lean out, it's just a bad idea all around.

So if your saw has a cat and a non-strato engine and conventional carb, then you have been ripped off by an organization that is either incompetent or unethical or otherwise unwilling or unable to invest in product development.

 

[srb08]

Thanks guys, Your explination on strato charging makes sense.

What I still don't understand is why husqvarna had cat mufflers in some 346xp's and not others and why some of the Jreds have cat mufflers while the Husq models don't?

I still don't completely understand the rev limited coils.