Muffler Mod for the 290,310,390

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southbound

Minister of Fire
May 26, 2008
733
mid south tn
All right jay here you go.....

"""DISCLAIMER ENTER AT OWN RISK MOD AT OWN RISK"""

This is how I mod my mufflers.. When I first started looking for a good how-to I found this setup on another site...

The first thing I would do is spray some PBblaster on the 3 nuts that hold the muffler on and let it set for a day...

Next make sure you have the drill bits ready and a drill.. I like to use my drill press..

The drill bit sizes I use are one 3/8 for the large hole in the middle and four 7/32 (because it is what I had) around the large hole.. If I do this again and I am not recommending it as I have yet to test but I think I will just drill 3 - 1/2 holes and be done with it...

Anyway I drill the holes in the indented part of the muffler under the front deflector..Why I drill there is because it is bypassing the baffles inside the muffler..If you have any experience with older saws you will see there are no baffles or need for them..

YES you do need back pressure tho..

YES you can drill to much and loose the ability to idle..

It is generally thought that 20% to 30% of the exhaust port is all you want to open it up...I have seen these saws with the entire indented portion removed but again I am not recommending it as I have yet to test this...

Ok now the holes are done and you have made sure no metal chips are inside the muffler..You can flush it out if you wish. You now need to open up the deflector..

To open up the deflector I take them to the belt sander and sand off the flat spot over the existing opening..You can use a file or a grinder but this mod will not be worth it if you don't open this up as well..

Ok so now some high temp stove paint and it is ready to go back together...Some folks leave out the screen some keep it in.. I keep mine and make sure it is clean...

Now for the most important part of all you have to retune the carb.. This has to be done so you don't run lean and (((SEIZE))) the saw....

Now most of these saws will still have the limiter caps in place..Now I have no pic's of these to show so hang in there with me..

On the side of the saw you will see the 3 screws used to adjust the carb. In this case you should only need to adjust the H but I pull the caps off of both the H and the L and end up having to adjust both..

Look inside the hole for the H screw and you will see a plastic looking screw with the slot for a flat screwdriver.. I use a 3 inch drywall screw..Place the screw in the hole and use the screwdriver to screw it into the cap.. It does not need to go in far just enough to get a bite..If it comes loose just do it again.. Ok this is when it gets tricky on these caps there is a key way you need to line up with the notch in the screw boot...Just pull up and twist it and you will feel it line up then just pull.. Now that you know what you are doing do the L also...

At this point the carb needs to be retuned.. I wont get into that as it sounds more like something for jay to cover...

Attempt this at own risk this was for your entertainment only!!!!!!!!!!!!!!!!!!

Ok jay so how do we tune a carb ;)
 

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smokinjay said:
southbound said:
smokinjay said:
I tune by ear in the cut through out the whole cut. Auto tune if you will. Thats what makes a winning saw..... ok ok I will find the llink here in a sec. on the laptop.
http://web.archive.org/web/20051018212959/www.madsens1.com/sawtune.htm

See I'm lazy I got a guy for that...

lol if I knew the 290 was the same as the 390 I had your pic. Done a few 390's I really like that saw with a few modds.

If I ever blow one of my 290's up it will come back as a 390...
 
southbound said:
smokinjay said:
southbound said:
smokinjay said:
I tune by ear in the cut through out the whole cut. Auto tune if you will. Thats what makes a winning saw..... ok ok I will find the llink here in a sec. on the laptop.
http://web.archive.org/web/20051018212959/www.madsens1.com/sawtune.htm

See I'm lazy I got a guy for that...

lol if I knew the 290 was the same as the 390 I had your pic. Done a few 390's I really like that saw with a few modds.

If I ever blow one of my 290's up it will come back as a 390...

I really think that would be very cool running at CO. fair they would not know what hit them. I'am not aware of it ever being done. 440/460 head been done alot.
 
How much extra power can one expect from a 310 w/ a muffler modification and properly tuned carb?
 
JDC said:
How much extra power can one expect from a 310 w/ a muffler modification and properly tuned carb?


10 percent
 
Want to see a gutted 064 muffler???

K here you go...
 

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JDC said:
Is it that noticable?

Yes, longer the cut or run the more you can tell.
 
southbound said:
Yes I wear earplugs!!!!


lol 064/066 I wear the radio head phones worth the extra coin if you run alot.
 
southbound said:
10% on something like a saw is more then what one would think..

A little port work and slam the head make it 20 percent and good chain work another 10-15 percent. This is much harder than a simple muff modd.
 
smokinjay said:
southbound said:
10% on something like a saw is more then what one would think..

A little port work and slam the head make it 20 percent and good chain work another 10-15 percent. This is much harder than a simple muff modd.


Now just what are you saying????


Not all of use can port a head.....
 
southbound said:
smokinjay said:
southbound said:
10% on something like a saw is more then what one would think..

A little port work and slam the head make it 20 percent and good chain work another 10-15 percent. This is much harder than a simple muff modd.


Now just what are you saying????


Not all of use can port a head.....

I know but chains are and easy one, and should always work on that one. You shold be able to port for me that much easier than the work you do....
 
southbound said:
Anyway I hear you got a guy....

I do and the machines.......
 
southbound said:
smokinjay said:
southbound said:
smokinjay said:
I tune by ear in the cut through out the whole cut. Auto tune if you will. Thats what makes a winning saw..... ok ok I will find the llink here in a sec. on the laptop.
http://web.archive.org/web/20051018212959/www.madsens1.com/sawtune.htm

See I'm lazy I got a guy for that...

lol if I knew the 290 was the same as the 390 I had your pic. Done a few 390's I really like that saw with a few modds.

If I ever blow one of my 290's up it will come back as a 390...

Ok, never seen this before... Different cyl and piston? What's the deal?

Matt
 
southbound said:
Difference between the 290 and 390????

P&C...The 390 gets a decomp valve too.......

Now You got to do it!
 
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