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Muffler mod issue..(another one)...

Started by mrcaptainbob, March 28, 2020, 11:07:46 PM

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mrcaptainbob

okay, so I have the (was) MS310 changed over to a (new) MS390 engine. Using all the original 310 engine parts. I suspect the carb will need to be re-tuned to match the new engine, but what about the muffler? The outlet holes seem awfully small compared to the inlet side of the muffler to allow better breathing. Making the holes larger, from what I've read here, seems like a sound idea. But I don't want to make them too large. What size should I make them?

 


 

Pine Ridge

Yes the carburetor will need to be tuned when you get it running. You will get some gains by modifying your muffler, it will breathe better and run cooler, and the exhaust outlets look very small on that muffller, so it will definitely benefit. If i were you i would look on youtube and see how others have opened up that particular muffler. 
Husqvarna 550xp , 2- 372xp and a 288xp, Chevy 4x4 winch truck

ehp

muffler can go up to 85% of the inlet area by volume for a muffler mod but I would do less , say 50% is a good amount on a saw like that . Just watch where you make the hole or holes bigger and make sure some kind of deflector in covering them cause ext going straight out the muffler onto wood will set wood on fire ok , yes you will need to reset carb

Fishnuts2

I add 3 similar shaped holes to the existing ones, and make all 5 larger. Stay away from drilling in the center "square portion".  Use the deflector cover to determine where you can locate the holes.

Air Lad

There are several youtube clips for the 039 {same muffler}
It's up to you how much material you chose to remove but once its gone {not impossible ,but} harder to put back

mrcaptainbob

Here's how I modified it...:

 
Anxious to get this all back together. I have an HF rpm meter. I like it a lot and will be using it to tune for the max rpm.
My plan is to put the sensor tape on the clutch cup face and mount the bar and chain without the side cover. I can get a clear reading that way. Some other chores are getting in the way, but I should have this done by week's end. Anxious!
I really, REALLY appreciate all your help on this project.
Thank you all!

John Mc

Quote from: mrcaptainbob on March 30, 2020, 06:21:03 PM
Anxious to get this all back together. I have an HF rpm meter. I like it a lot and will be using it to tune for the max rpm.
My plan is to put the sensor tape on the clutch cup face and mount the bar and chain without the side cover. I can get a clear reading that way. Some other chores are getting in the way, but I should have this done by week's end. Anxious!
I really, REALLY appreciate all your help on this project.
Thank you all!
Be aware that a lot of RPM meters aren't useful for tuning chainsaws: they either can't handle that high an RPM and/or their response time is too slow to accurately catch what is going on.

Yo might be better off tuning by ear. Madsens has a good explanation of how to do this on their saw tuning page, including audio files so you know what to listen for (You'll need better speakers than what are in most laptops or a good set of headphones to clearly hear what is going on.)
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

mrcaptainbob

According to my HF tach it was running at 13200 when first started. Tweaked it to 12800. Will do some cutting tommorow to see how it does in the real world. Idles fine, sounds good. So far.

Al_Smith

Best advice using a tach is leave it in your tool box .Then set the high speed jet so it acts like it'd slightly loading up .Then make a cut and it should clean up.Make couple of  cuts to check it .Then get the tach out ,that's where it runs . 

John Mc

Quote from: Al_Smith on April 08, 2020, 02:01:56 AM
Best advice using a tach is leave it in your tool box .Then set the high speed jet so it acts like it'd slightly loading up .Then make a cut and it should clean up.Make couple of  cuts to check it .Then get the tach out ,that's where it runs .
X2.

Use it to verify your tuning my ear, especially until you have conficence in what you are hearing. That procedure is described in more detail with audio files in the Madsen's link I posted earlier.
If the only tool you have is a hammer, you tend to see every problem as a nail.   - Abraham Maslow

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