Echo 590 factory settings and break in...

[Forestviller]

I was gentle breaking in a new cs590 and finally hit full rev today after a few tanks so I decided to pull the carb adjust limiters to tune beyond factory (and at the same time cut out the muffler outlet cap's 180 bend which is common to do). It turns out that all this time during break in the factory high needle was only open 3/8 of a turn! My spark plug is pasty white. I haven't run the saw for more than a few cuts at a time and it never felt hot at all, plus I always give gentle throttle to cool it before shutting down or after a cut. And again, it hasn't hit WOP more than a handful of times
I'm totally bummed that I trusted the factory settings and I'm worried if it was enough to do any damage given the plug color? Now that I richened and adjusted the carb how long until the plug would reflect the true difference? I'd appreciate thoughts for future understanding.
Also a random question, the thin plate on the muffler front that covers two holes in the muffler...what is that and why? After cutting out the baffle plate I'm curious why that's there as most saws have no plate over those two holes on the muffler front.
Newbie questions...

 

[rmh3481]

I doubt there is any trouble. These models come with a carb that has a small bypass valve built into it. Its part of the high speed fuel feed and was done for warranty purposes. My 600p has it. Walbro HDA 268. If your curious take the metering cover off and take a look. I would be wondering about that white spark plug though. Maybe step that down a heat range.

Edit-
Forgot to mention that the 590 and 600 come with limited ignitions that drop spark making the engine sound like its four stroking when its not. Use a tach to set the upper limit rpm.

 

[Forestviller]

I doubt there is any trouble. These models come with a carb that has a small bypass valve built into it. Its part of the high speed fuel feed and was done for warranty purposes. My 600p has it. Walbro HDA 268. If your curious take the metering cover off and take a look. I would be wondering about that white spark plug though. Maybe step that down a heat range.

Edit-
Forgot to mention that the 590 and 600 come with limited ignitions that drop spark making the engine sound like its four stroking when its not. Use a tach to set the upper limit rpm.

Where's the metering cover and what should I look for to see if there's a bypass? Good info and thanks, it runs well so I'm not too concerned but I'd like to understand it better.

 

[rmh3481]

The metering cover is on the carb, over the metering chamber. If your not familiar dont take it apart, just understand its there.

Most of the carbs sit above the fuel tank, so the mix has to get up there somehow. This is done by the pump side of the carb. There are small diaphragms on the pump side that work to move the fuel to the carb.

On the opposite side of the carb is the metering chamber. Fuel is transferred from the pump side to the metering side by a needle valve and lever. From this metering chamber, the twist jets feed the engine its metered fuel.

Due to environmental factors such as heat, barometric pressure, altitude and so on, the engine needs varying amounts of fuel to do its job. In times past this additional fuel was burned or discarded into the environment. Today as you know its a much different story with lean settings and catalytic converters applied to small two strokes.

Because the EPA watches Echo, their engines seem to always be sold or set up to run lean. To aid against warranty claims the engineers added a by pass jet to the metering chamber which provides a slight amount of additional metered fuel to the engine during peak load. This fuel is metered through a fixed jet hidden in the metering chamber of the carb. This jet is designed to only flow when barometric pressure is at its lowest (think vacuum high). This Walbro system was previously known as a semi fixed jet metering system, and was first used by Husqvarna.

The engine is tuned off the twist jets like normal and you will probably never know that the semi fixed jet system is there. Just be mindful of the ignition limiter used on the 590 and 600p which can imitate the traditional 4 stroking sound. Use a tach to set the upper limit rpm. The 620 doesnt use the limited ignition.

 

[Forestviller]

I'll have to pick up a tach to experiment with my tuning and ear but I read that the upper shouldn't be set without being under load on the 590 due to the rev limiter? I'd think a proper tune without load would give a proper tune with a load, a bit confused by how that works if all a load does is limit the revs.
Thanks for the info, it's great help.