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First Time woods port 390xp

Discussion in 'Saw Building 101' started by Jfox8807, Sep 15, 2017.

  1. Jfox8807

    Jfox8807 ArboristSite Lurker

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    So after combing thru the forum, I finally said let's try it. I bought me a flexshaft grinder and various bits and went to it. I didn't have a degree wheel so I didn't take any timing numbers. I just tried to not change it any.
    I widened intake and exhaust port to roughly 70% of bore. I left the intake ruff and tried to polish the exhaust some to help minimize carbon build up. I don't have a 90* hand piece.
     
  2. Jfox8807

    Jfox8807 ArboristSite Lurker

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    So I didn't do anything to the outlets of the transfers. I just cleaned up the bottom side as far as I could reach in there.
    All pic are In progress
    Exhaust
    IMG_0724.JPG IMG_0723.JPG

    Intake I didn't get a pic when it was finished for some reason only the left side is done here
    IMG_0726.JPG
     

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  3. Jfox8807

    Jfox8807 ArboristSite Lurker

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    But I had a few questions. I measured my squish in four places. Three measured right at .020, but one place measured .017. This was taken with out gasket installed. Is that a safe squish for a 390xp?

    Also how important is an unlimited ignition for performance?

    Where's the best place to purchase an unlimited ignition?

    Do these saw need any ignition timing advance? If so how much?

    Any comment or pointers are welcome just keep it nice it's my first one ever. I'm just learning.
    Thanks in advance have a great day.
     
  4. Ketchup

    Ketchup Smells like 2-stroke.

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    How did this turn out for you? I'm about to dive in to a 385 and gathering info. .017 seems pretty tight, did it survive? Looks like solid work.
     
  5. Jfox8807

    Jfox8807 ArboristSite Lurker

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    It turned out great. I put it back together with a gasket I'll find a machinists one day to deck the jug but for now it's still a beast
     
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  6. trappermike

    trappermike ArboristSite Guru

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    Your work looks pretty good but I would put a bit smoother finish for the intake and transfers,not polished though. With 70% port width I hope you put a very large chamfer on the top and bottom edge of the intake and exhaust ports or disaster WILL occur. I would not worry about the squish being .003" too tight,it's ok. You could advance the timing 2 degrees with the keyway safely. Great port work though,well done! Ask about an unlimited ignition in the normal saw forum...
    But for competition you need something better than the puny stock carb,the only choice is the Tillotson HT from an early 084,it may be some work to adapt it. And you will need a pipe. I believe your saw could be very competitive,if your exhaust port duration is in the right range.
     
  7. trappermike

    trappermike ArboristSite Guru

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    70% port width is too much for a work saw to survive long though unless you really chamfer the ports well and hope for the best.
     
  8. Ketchup

    Ketchup Smells like 2-stroke.

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    What's the range for exhaust duration on a 390?
     
  9. trappermike

    trappermike ArboristSite Guru

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    For a work saw I would say up to 176 degrees(Now others will dispute this with their own idea). For competition 180 plus, depending on what you intend to use it for... I'm guessing the saw in the photos has at least that or more. But as you increase duration you will lose some mid range power too.
    This saw should really make good power,but I think the ports are too wide and large to be a work saw that will last long hours of running. A modded work 390 needs a good free-flowing muffler and modified carb,either stocker or Walbro WJ.
     
  10. Ketchup

    Ketchup Smells like 2-stroke.

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    Good to know. I'm about to port my 385 for the woods. What kind of carb mods are you talking about? Opening the jet? Would an 084 HT be bad for a woods port or just unnecessary? The carb upgrades I've done so far were really great, but have all been easy.
     
  11. trappermike

    trappermike ArboristSite Guru

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    An 084 carb would not good for a modded work 385,and you will have to get inventive to fit one on if it were for competition.
     
  12. Huskybill

    Huskybill ArboristSite Guru

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    I’m going to purchase a separate saw to build a ported saw. Sounds good.

    They offer a little diameter flapping drums on Amazon.
     
  13. trappermike

    trappermike ArboristSite Guru

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    For a modded 385 I would bore the stock carb larger(See my Carb Boring thread)it will make more power for little cost or effort.
    For sanding and polishing,a simple tool I make is to take a 1/4" bolt about 4" long(for dremels with 1/4" bits),cut the hex-head off and hacksaw a slot in one end about 3/4" deep. Then you can rip off some 1" wide strips from sheets of emery cloth of any grit you desire for smoothing and finishing with the tool. I sometimes start off with medium grit after rough grinding,then finish with 400 grit,depending on the finish I want. You can make your emery "roll" on the tool any size for your needs as you go...
     
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  14. huskyboy

    huskyboy ArboristSite Operative

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    I would get rid of the gasket. .017 is fine. Use anerobic 518 sealant or motoseal/threebond/yamabond/hondabond. I’ve checked squish on a few cylinders that varied slightly on one corner just like yours, which is why it’s important to check all 4 corners. Advance it 1/3 keyway or a tad less. Unlimited coil doesn’t make it faster...just easier to tune. Healthy muff mod under deflector and match gasket/muff to cylinder. The stock carburetor should be fine for a worksaw. Nice grinding by the way!
     
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  15. cus_deluxe

    cus_deluxe Thats what she said.

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    If i wanna gain a few thousandths clearance i just make a beer can gasket, good for .004 or a touch more
     
  16. Huskybill

    Huskybill ArboristSite Guru

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    I had a 288 modded and a ported 2100. They were my buddy’s saws we raced at the local fairs. I ran the 288 to break it in cutting firewood. So I knew how the saw handled. I cleaned house at the fair in speed cutting with the 288. The five contenders all used my 288 I was the last to run it and she was warmed up. The hotter she got the faster she cut.

    Time to gather up my porting tools.
     

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