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Muffler Mod for the 290,310,390

Post in 'The Gear' started by southbound, Jan 22, 2011.

  1. southbound

    southbound Minister of Fire

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    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 ;)

    Attached Files:

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  2. smokinj

    smokinj Minister of Fire

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  3. southbound

    southbound Minister of Fire

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  4. smokinj

    smokinj Minister of Fire

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    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.
  5. southbound

    southbound Minister of Fire

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

    smokinj Minister of Fire

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    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.
  7. JDC1

    JDC1 Feeling the Heat

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    How much extra power can one expect from a 310 w/ a muffler modification and properly tuned carb?
  8. smokinj

    smokinj Minister of Fire

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    10 percent
  9. JDC1

    JDC1 Feeling the Heat

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    Is it that noticable?
  10. southbound

    southbound Minister of Fire

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    Want to see a gutted 064 muffler???

    K here you go...

    Attached Files:

  11. southbound

    southbound Minister of Fire

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    Yes I wear earplugs!!!!
  12. smokinj

    smokinj Minister of Fire

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    Yes, longer the cut or run the more you can tell.
  13. southbound

    southbound Minister of Fire

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    10% on something like a saw is more then what one would think..
  14. smokinj

    smokinj Minister of Fire

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    lol 064/066 I wear the radio head phones worth the extra coin if you run alot.
  15. smokinj

    smokinj Minister of Fire

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    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.
  16. southbound

    southbound Minister of Fire

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    Now just what are you saying????


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

    smokinj Minister of Fire

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    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....
  18. southbound

    southbound Minister of Fire

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    I drink to much for that...One slip and it's time for a new head..

    I just don't like the odds.....
  19. southbound

    southbound Minister of Fire

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    Anyway I hear you got a guy....
  20. smokinj

    smokinj Minister of Fire

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    I do and the machines.......
  21. southbound

    southbound Minister of Fire

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    Do I smell a road trip??????????????????

    I see that going over with the wife..Although you never know...
  22. EatenByLimestone

    EatenByLimestone Minister of Fire

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

    Matt
  23. southbound

    southbound Minister of Fire

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    Difference between the 290 and 390????

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

    southbound Minister of Fire

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    There is something else carb maybe can't remember...
  25. smokinj

    smokinj Minister of Fire

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    Now You got to do it!

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