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Ported 390xp Fuelling issue.

Discussion in 'Modded Work Saws' started by revyfaller, Dec 22, 2019.

  1. revyfaller

    revyfaller ArboristSite Lurker

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    hey there, looking for some help with a saw. I put a new bottom end and jug & piston on a tired 390 I had, and while I was at it did some minor porting work to it. Case matched the transfers via the gasket and took some outta the exhaust and intake. Didn't go crazy by any means. Upon re-assembly it seems to be over fuelling like crazy, I got it to bark up briefly but that didn't last long and it bogged out. Ive cleaned the carb, new plug, cleaned tank vent, new fuel filter, checked gapping on the coil, blew out fuel lines thinking maybe there was siphoning happening. Ive tried all kinds of stuff but I can't seem to get it to fire!

    Wondering how crucial the unlimited coil is to this and if that may be my issue? It has the stock blue coil.

    Any tips would be appreciated, thanks.
     
  2. jrwied

    jrwied ArboristSite Operative

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    Flywheel key ? Timing off?
     
  3. Duce

    Duce Addicted to ArboristSite

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    I assume muffler screen is clean?
     
  4. Yotaismygame

    Yotaismygame Juiced Saws #GetJuiced

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    Visit the carb again. Could be worn out parts, or something stuck in it.
     
  5. revyfaller

    revyfaller ArboristSite Lurker

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    Right, that's probably exactly what it is. The key sheard off, hasn't even thought about that! Thanks
     
  6. revyfaller

    revyfaller ArboristSite Lurker

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    Unsuccessful with the timing key on the flywheel.. Seems to be my impulse line is seriously full of fuel, going to pressure/vaccum test the lines soon and see what happens.
     
  7. revyfaller

    revyfaller ArboristSite Lurker

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    starting to think this is most likely what happening.
     
  8. revyfaller

    revyfaller ArboristSite Lurker

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    @blsnelling have you ever come upon porting gone to far resulting in over fuelling? i understand there's many variables that you can't see, maybe ill pull the cylinder off and take some pics. also I have never done this before haha.
     
  9. revyfaller

    revyfaller ArboristSite Lurker

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    Have a pic of the exhaust port. Maybe I'm out to lunch!
     

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  10. jrwied

    jrwied ArboristSite Operative

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    Looks soaked? Is that all fuel? Maybe dry it out good. Pull plug let it all dry while u go over your carb. And settings.
     
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  11. blsnelling

    blsnelling Site Contributor

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    No. Have you put a degree wheel on it?
     
  12. Ketchup

    Ketchup Smells like 2-stroke.

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    Here’s some thoughts:

    Flywheel:
    Definitely put a new key in it.

    Carb:
    Lever too high?
    Worn main needle?
    L & H screws reversed?
    Diaphragm gaskets in the wrong order?

    Coil:
    Suspect, but typically effects higher RPM or has erratic/no spark.

    Porting:
    A VERY low intake (80 degrees or higher) could be a problem, but soumds like you were conservative.

    Is your plug wet? Sounds like your case is badly flooded (impulse full of fuel). Lack of fuel up top would indicate major freeporting and lack of transfer pressure.

    I would install a new key and pull the carb and plug. Run the piston up so the intake is open and tip the saw up so the case drains out the intake. Check your carb for lever height, gaskets in the wrong order, screws properly set. Check spark. Reassemble. Try a normal starting procedure.

    I’m guessing you have a carb issue, but who knows?
     
  13. blsnelling

    blsnelling Site Contributor

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    It's cast into the flywheel.
     
  14. blsnelling

    blsnelling Site Contributor

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    I port them to 85* by design.
     
  15. Ketchup

    Ketchup Smells like 2-stroke.

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    Haha, guess I shouldn’t post from memory.

    Cast Flywheel keys are a bummer when they shear. I would try to find a non sheared one to test with. The FW timing is something you want to rule out. You can properly align a FW with no key, but it leaves some doubt in your troubleshooting.

    Thanks for sharing Brad! I’m sure a Snellerized 390 is a force to be reckoned with. The point is well made too: intake porting is almost definitely not the problem.
     
  16. revyfaller

    revyfaller ArboristSite Lurker

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    Got around to setting up a degree wheel, ended up with these numbers. Intake: 83 Exhaust: 95. These seem outta control at all? took a few pictures of the cylinder, just from looking at it my intake port looks massively wider than my exhaust, would that make my intake duration too long and maybe that's where all this fuel is coming from? Would matching my exhaust too the intake more help flow that out? IMG_0878.jpeg IMG_0879.jpeg IMG_0880.jpeg

    Reminder* This is my first go around so it could be ****ed! Also that isn't a chip in the nikasil, just where the die grinder poked a little extra.

    Thanks for the input @Ketchup @blsnelling
     
  17. blsnelling

    blsnelling Site Contributor

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    I run the intake at 85 and wide. Exhaust is about 96 from the factory. So, those numbers are not your problem.
     
  18. blsnelling

    blsnelling Site Contributor

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    Lay a base gasket on the base of the cylinder and case match it.
     
  19. revyfaller

    revyfaller ArboristSite Lurker

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    Huh. Okay I’ll case match that tomorrow, rebuild my carb and see what happens. Thanks again.
     
  20. revyfaller

    revyfaller ArboristSite Lurker

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    She’s alive and runs dam good! I’ll post up a video soon, thanks for the tips. Dug into the carb and found a small tear in one of the screens underneath the impulse line. Had me stumped as this carb ran great on the saw I pulled it off of.
     
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