muffler mod question

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pyroholic

pyroholic

Member
Feb 17, 2013
219
Mid-Michigan
Did a muffler mod on my friend's ms311. Made a bit of difference, but my question is in the tuning. Starting out the carb screw's were in the factory position H=¾ turn out, L=1. After the mod it tuned to L = ¾( leaner than before) and H = 1-¼. H seems reasonable, but why would the L come in leaner?
 
Didn't do too extreme of a mod, but here is a picture. We have a screen and deflector ordered that will retrofit nicely. Want to make it look trick, not like we just drilled a hole. Leaves a little more mystery for the folks that don't understand. Screenshot_2013-08-12-18-04-56.png
 
Wide open no screen?

Just a guess but maybe it wasn't tuned properly to begin with, or you are tuning in a different climate than before (summer to winter should be leaner in summer.)
 
That's what I would expect. Leaner means more rpm's and that's what a muff job does.
 
he's talking on the L jet, leaner down low has nothing to do with top end. muffler mods do not always mean more rpm. It needs more fuel up top (h) because it is getting the burnt mixture out faster that it was, as a result takes in more air so it needs more fuel. Just opening the muffler rarely raises the max rpm. That is done from porting.

As others have stated, you usually don't have to mess with the L jet screw at all. But if it is idleing fine and it transitions from idle to wide open, then it is good. if it hesitates the least little bit from idle to wot, then the L screw needs backed out a tad. and weather does play a roll on tuning.
 
Freakingstang said:
he's talking on the L jet, leaner down low has nothing to do with top end. muffler mods do not always mean more rpm. It needs more fuel up top (h) because it is getting the burnt mixture out faster that it was, as a result takes in more air so it needs more fuel. Just opening the muffler rarely raises the max rpm. That is done from porting.

As others have stated, you usually don't have to mess with the L jet screw at all. But if it is idleing fine and it transitions from idle to wide open, then it is good. if it hesitates the least little bit from idle to wot, then the L screw needs backed out a tad. and weather does play a roll on tuning.
Click to expand...

Never seen a muff modd that didn't bring 800-1000 more rpm's. Unless its and older stihl 0 style.
 
most of the ones I've seen run around 4-600.. if it is more than that, it is usually a tad on the lean side. i'd rather have a little fudge factor. tuning in the summer will like result in a melted saw come 20 degree winter air (cool dense air more volume). Not 100% on the brand new saws as I haven't messed with anthing newer than an Xtorq 372 a couple years ago. most saws these days have a rev limiter anyways and without using a tach it is almost impossible to set rpm by ear. The older 0 series 044/46/64/66 saws had much larger and in most instances dual ports and don't improve power on a stock saw, now porting throws the numbers quite a bit..
 
Freakingstang said:
most of the ones I've seen run around 4-600.. if it is more than that, it is usually a tad on the lean side. i'd rather have a little fudge factor. tuning in the summer will like result in a melted saw come 20 degree winter air (cool dense air more volume). Not 100% on the brand new saws as I haven't messed with anthing newer than an Xtorq 372 a couple years ago. most saws these days have a rev limiter anyways and without using a tach it is almost impossible to set rpm by ear. The older 0 series 044/46/64/66 saws had much larger and in most instances dual ports and don't improve power on a stock saw, now porting throws the numbers quite a bit..
Click to expand...

That's why I excluded 0 style. 460 for example gain and easy 1000 rpm and still on the fat side. No mention of limits being off from the OP. ;)
 
Has a screen and deflector now, had to order that. Yes pulled the limiters. I wondered about the weather and planned on retuning when colder just in case. Saw is running good, and is better than stock in the cut. The results of the tuning, as in the screw positions, was a much different result than the 290(which also needed richening on the L screw just to stay running after the mod).

My only thought was that the limiter cap may limit both too lean and too rich on the L screw which would throw off the turn count from before doing anything to a finished job. Not sure about that, just a theory.

Either way they are both running great.
 
Are you tuning by ear or tack?
 
Well, both kinda. I have a tach, but it has such a slow refresh rate it's kinda useless on the top end. I followed MasterMech's instructions through the L screw with the tach then did the top by ear. I can't bring myself to hold WOT long enough for the tach to read. It would take 10+ seconds to get a top read. Definitely four stroking, maybe a little fat if anything, but cutting great! Very great!

Any suggestions on a decent tach that won't break the bank?

As always, I appreciate the help y'all offer!
 
I have the tech-tach. Same price but is bigger and uses a 9v battery. Works great, I figured the bigger size would keep me from putting it in my back pocket and breaking it when I sit on it... It's not that big that you can't hold it with one hand while running the saw. And it has wires, but I've yet to try it with the wires hooked up.
 
pyroholic said:
Well, both kinda. I have a tach, but it has such a slow refresh rate it's kinda useless on the top end. I followed MasterMech's instructions through the L screw with the tach then did the top by ear. I can't bring myself to hold WOT long enough for the tach to read. It would take 10+ seconds to get a top read. Definitely four stroking, maybe a little fat if anything, but cutting great! Very great!

Any suggestions on a decent tach that won't break the bank?

As always, I appreciate the help y'all offer!
Click to expand...

Just wondering how you was doing it. By ear is better than most tachs but you already figured that out.
 
Like Mike, I also opted for the Tech Tach TT-20K, over the Fast Tach. I can't say I had experience with either, but after reading up on both, the Tech Tach seemed like the better option for me. I'm happy with it.
 
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