4 mill banshee tuning

Discussion in 'Yamaha' started by fullthrottle, Jan 20, 2016.

  1. fullthrottle

    fullthrottle Member

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    So i figured before i signed up on another site i would see if any of you guys would be able to set me in the right direction with this. Im looking at buying a banshee that has a freshly built engine with 4mil cranks, porting (not sure how agressive) chariot cool head, 19cc domes, and v force 4 reeds. The only problem is the carbs are stock with bigger jets but its not tuned right. The question is will stock carbs even work with this setup with the right jetting or would it need bigger carbs.(if so how big?) im somewhat new to tuning 2 strokes but have been learning the basics on my blaster with jetting, plug chops etc.
     
  2. Jimmer

    Jimmer Member

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    I run a 4mm stroker with ported cylinder and VForce4 reeds also. My carb choice is a 36mm TM Mikuni. You are strangling it with a small carb. Edit: I just realized now it says Banshee, but I feel mostly the same.
     
    Last edited: Jan 21, 2016
  3. fullthrottle

    fullthrottle Member

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    I would eventually want to go to bigger carbs but could i just jet the stock carbs or will it not work at all?
     
  4. Jimmer

    Jimmer Member

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    They will work.
     
  5. fullthrottle

    fullthrottle Member

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    Ok thanks for the info. I know it has 320 jets now. Do you know around what size i would need to start at when i rejet it?
     
  6. Larry's Shee

    Larry's Shee Active Member

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    First thing would be a leak test.
    More info about set up, how it runs now, why you think it needs rejet? What fuel you using? Results of compression test would help also. Temperature and elevation would would help.
     
  7. fullthrottle

    fullthrottle Member

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    Im going look at it and probably buying it Saturday. I know that it doesn't run very good now.(not sure if rich or lean) I will do a leak test but the motor is freshly built so it shouldn't leak. Im not sure why the current owner had an engine built and never tuned the carbs but i am getting a really good deal on it.
     
  8. jus_me

    jus_me Active Member

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    This could be the whole reason right there. If after the rebuild it wasn't leak tested and had a decent air leak it would never run right no matter how much tuning/jetting anyone did.
     
  9. fullthrottle

    fullthrottle Member

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    Never really thought about that! I will definitely check it out. Im most likely gonna buy it and even if i have to go in and put new gaskets it will be worth it. Thanks alot for the info. I will post how it goes when i get the bike
     
  10. Larry's Shee

    Larry's Shee Active Member

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    What is your definition of "good deal" ?
    Fixing someone's FUBAR can be costly !! Be careful !!
    But can also be a good deal !!

    Believe it or not, a Banshee is easier (in some ways) to work on than a Blaster

    Try to get as much info before you buy. Either receipts or proof of parts, especially the crank, maybe porting.
     
  11. fullthrottle

    fullthrottle Member

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    Well ive been watching craigslist and Louisiana sportsman for a few years now and this is the cheapest ive seen a running banshee go for. Its $1300 and he did send me a running video today and it really sounds healthy and was smoking like a banshee usually does so im not sure exactly what its doing wrong. Im going look at it in the morning so hopefully it goes well. I will try to get proof of all the work done to it. Thanks alot for the help
     
  12. Larry's Shee

    Larry's Shee Active Member

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    Freshly built means little to nothing as far as leaks, ALLWAYS best to test. You (we) have no idea if new seals were used with new crank (a must) or a dozen other possibities.

    Also if you get it, you may need to run race fuel because of the dome size.
    Also, carbs may be OK, depending on rest of setup and intended use.
     
  13. fullthrottle

    fullthrottle Member

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    So i did end up getting it and i talked him down to 1000. Ive only been able to start it a few times. When it does start it runs strong up to where the power band feels like it should be then starts spitting and sputtering. Also if i start it, it will start again for a little bit but of i let it sit for more than a minute or so it wont start. Im still working on leak testing it because freeze plugs wouldnt work on the exhaust side because the bottom of the holes are flat. Im going to get some radiator hose that fits over the exhaust side to cap it off and leak test it. Im also going to pick up a compression tester just to be sure the engine is fresh as the guy said it was. I also ordered a few sizes bigger of jets to throw in it once i get the leak test figured out.
     
  14. fullthrottle

    fullthrottle Member

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    150 psi of compression!!! Still working on the leak test.
     
  15. dirtysquared

    dirtysquared DirtyDirty

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    I'd up the carbs. Not saying that the stocks will not work, but there are better options out there for you.

    If you don't have one, get a carb sync tool....it makes life alot easier.
     
  16. fullthrottle

    fullthrottle Member

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    I do want to go to bigger carbs eventually but right now im just trying to get the thing to run. What exactly does a carb sync tool do? I just eyeballed it when i did it.


    Also if anybody could give me some info on where to start with jets that would be great! I have 330s now and have a couple other size mains and a 27.5 pilot on the way. Im hoping the pilot helps with the starting issue but i doubt thats the problem.
     
  17. fullthrottle

    fullthrottle Member

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    Also can anyone tell me how to tell if my timing is right? Im wondering if the whole issue is timing. Doesnt the timing need to be later with a +4 mil stroke?
     
  18. Blaaster

    Blaaster Moderator Staff Member Technician Forum Supporter

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    Timing should be the same with any stroke, the piston still gets to the correct place no matter the length of the stroke.
     
  19. Larry's Shee

    Larry's Shee Active Member

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    Need more info. Pipes , temps, elevation.
    Son's nonported 4mil with fmf was at 300, changed to DMC 916 had to bump up to 330 (summer). Float level is important too, had to go from 27.5 to 30p to cure starting ills.
     
  20. fullthrottle

    fullthrottle Member

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    Im in south Louisiana about 45ft above sea level. The weather has been anywhere from 40 to 70 degrees. FMF pipes. What are you guys using to measure float height? On my blaster i got it close with a ruler that had cm but i cant seem to find a mm ruler and should it just be at the stock 21-22mm? I know its close but not perfect
     

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