Echo 355T tuning difficulties...

LordFarkwad

Well-Known Member
Location
Chatham Co.
I wanted to do a ground-up tune on my 355T that I muffler modded a few days ago, and so I seated the low and high jets, as well as the idle screw (everything clockwise, in other words). I'm assuming that the idle screw being all the way seated means that the butterfly/ is fully shut.

Where things currently stand, the saw surges at idle - low, high, low, high, etc. There are also a number of symptoms that are unexpected, at least for me with my small amount of saw-tuning experience...

- with the idle screw fully seated, the low jet can be adjusted so that the saw still idles.
- the low jet, when leaned out, can be adjusted such that the saw could literally cut wood; probably turning 8000 rpm (I've not measured that, but all I'm trying to say is that it's turning fast).
-
the peak that I'd expected to get when turning the low jet between lean and rich mixture is not only super-wide, but also super-high RPM (sort of a carryover from the above bullet).

I've not removed the carb and cleaned it, but I did take a look at the spark plug, and it was 100% fine, no issues there. I knocked off the air filter by hand, but it didn't look too terribly bad. Should I remove the cover/air-filter and see if that makes the surging go away? I suspected something was up with the carb based on the observations recorded in the bullet points, personally.

Can you guys help me diagnose what might be going on and what I should check?

 
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LordFarkwad

Well-Known Member
Location
Chatham Co.
Addendum...

I have it on good authority that my understanding of the idle screw adjustment is backwards - in other words, all the way 'seated' on that guy equates to opening the throttle.

So, that explains the low jet being able to take it up to 8000 rpms, at least. Derrrrrrr
 

Birdyman88

Well-Known Member
Location
Arlington
I have it on good authority that my understanding of the idle screw adjustment is backwards
That is correct. Turning idle screw clockwise opens butterfly and increases rpms.

If you start with factory settings, turn the idle clockwise until the saw stays running and it idles a little higher than normal. Next, turn the low jet adjustment clockwise - rpms increase up to a point and the saw will begin to surge intermittently - then keep turn CW until rpms start to decrease and saw may die. Make note of the peak rpm position, turn low CCW back to that position, then from that position rotate CCW an additional 1/4-1/2 turn until saw idles smooth without surging. Rpms should still be high due to idle adjustment, and the final best position of low jet is very much saw dependent. Once there, decrease (or increase) idle to achieve factory idle rpm spec. This will give you a good initial idle and low jet setting that only needs to be adjusted for environmental, fuel, or air filter conditions.
 

LordFarkwad

Well-Known Member
Location
Chatham Co.
You reckon the surging is indicative that I've got a carb issue? Like I say, I've not checked the normal stuff like fuel filter and whatever air inlet there is in the fuel cap (there is one on the 355, right?), so that is next. But, I was hoping that perhaps me having that idle screw in all the way might have been the source of some of the surging, as that surely put it in a fonky operating condition to have had the throttle open enough to produce 8k with the right mixture, but then the mixture rich enough to take it down near proper idling rpm's.hahaha

Edit: it didn't have any carb issues before, so besides the surging with the really whacked out adjustment, I've got no reason to think it has an issue. Just inquiring.
 
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Serf Life

Well-Known Member
Location
Maine Island
From what I’ve read, you may have to pull the limiters to richen it enough post-mod as Echos are generally lean from factory. A friends saw was acting like that (not after a muff mod) and it was an air leak from a boot off the carb. Let is know how it compares to stock once its ripping again.
 

dsptech

Well-Known Member
Location
North East
At least it wasn't running too lean :LOL:
That is typical on this saw if not adjusted correctly.
This saw is very sensitive to slight adjustments.
After each adjustment rev the saw a couple of times and let it settle down before adjusting further.
You must have pulled the limiter caps if you are seating the low / high screws all the way in.
If you did not pull the caps then you are not fully seating the screws.
 

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