adjustments 4 elevation change ?
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adjustments 4 elevation change ?

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    Senior Member 74glencoe's Avatar
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    Default adjustments 4 elevation change ?

    What I will run into with the elevation change from about 4,400 ft to 500 ft. I want to go cruise around Belton lake this upcoming or the next weeked. The boat runs very well at my elevation, but I know there will be atleast some carb tuning involved, Any tips on that or anything else you guys think I may be getting myself into will be greatly appreciated. Motor is a 455 olds, big valve heads (g), torker intake, 750cfm elelbrock performer, no idea on the cam but pretty sure it is not stock. Thanks to all who chime in.
    Boating is nothing like cocaine, boating is much more addictive and results in bigger parties!

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    " Live Laterally " Dominator's Avatar
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    Lets see. From higher to lower you will be running LEAN!!! You going to want to bump 2 at a time. YOu shouldnt need to go more then 4 sizes down. If I am wrong im sure I will be corrected here shortly. What I have found easiest is have 2 carbs. One for low level and one for home. Just my .02
    " NO MOTOR NO BOATER "

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    Senior Member 74glencoe's Avatar
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    So there is no way i can make it up with the mixture screws, i need to re-jet?
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    Senior Member ap67et10's Avatar
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    Quote Originally Posted by 74glencoe View Post
    So there is no way i can make it up with the mixture screws, i need to re-jet?
    i'm going to go out on a limb here, but did you ever rejet...or even touch your carb other than the mixture screws for you elevation? My dads boat runs pretty good up high at 5500 ft, but just a little fat...nothing that makes much of a difference. when he brings it back down to run at sea level all he does is....well...nothing, and it does just fine. its just a pretty much stock BBC that doesn't see more than 5000rpms at any point in its life. I would say if you never touched it from the beginning, other than idle and mixture, and you have a stock edelbrock on there, i'd say you can probably take it down and not touch anything. i bet it will fire up and run just fine for what you have and what you are doing. if you want to play it extra safe than you can get a jet kit, but i don't think you'll need it for what you have.

    AP

  7. #5
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    The rule of thumb is (1) jet size for every 2000' in elevation change.
    In your situation this rule would mean you increase your jet size by (2).

    For example if your running 75 mains on the primaries, and you drop 4000' in elevation, you would move up to 77 mains and so on.

    The mixture screws are for your idle fuel mixture, you may have to open them up a little to smooth the idle out, but your not making a huge shift in elevation IMO so this will be an on the fly decision on your part.
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    Senior Member 74glencoe's Avatar
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    Quote Originally Posted by ap67et10 View Post
    i'm going to go out on a limb here, but did you ever rejet...or even touch your carb other than the mixture screws for you elevation? My dads boat runs pretty good up high at 5500 ft, but just a little fat...nothing that makes much of a difference. when he brings it back down to run at sea level all he does is....well...nothing, and it does just fine. its just a pretty much stock BBC that doesn't see more than 5000rpms at any point in its life. I would say if you never touched it from the beginning, other than idle and mixture, and you have a stock edelbrock on there, i'd say you can probably take it down and not touch anything. i bet it will fire up and run just fine for what you have and what you are doing. if you want to play it extra safe than you can get a jet kit, but i don't think you'll need it for what you have.

    AP
    I have rebuilt my carb and a few others, but never re-jetted one, but since taking a little look at my edelbrock owners manual I see that I have completely shown my ignorance when it comes to carbs. (mixture screws are only for idle ) anyway, now that I think about it you are probably right seeing how as I bought the boat in cali and have not changed the jets, or rods as of yet. And seeing how its an olds you have the "never sees north of 5000 rpm pegged, I dont want to see parts fly everywhere. Thanks for the lesson.
    Last edited by 74glencoe; 10-18-2009 at 10:42 PM.
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    Senior Member H20MOFO's Avatar
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    I didn't see anyone mention timing. Depending on how tightly your timed right now, you may find you need to take a couple of degrees out. If your timed conservativly now you'll probably be o.k. If nothing else keep an ear out for detonation.
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    Senior Member 74glencoe's Avatar
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    Quote Originally Posted by H20MOFO View Post
    I didn't see anyone mention timing. Depending on how tightly your timed right now, you may find you need to take a couple of degrees out. If your timed conservativly now you'll probably be o.k. If nothing else keep an ear out for detonation.
    That is what I was lookin for, I will keep detonation in mind. I picked up a "calibration kit" for my carb, it has quite a few jets and metering rods for the primary jets so even if ap is wrong i think I will be ok with that and the jetting chart. Thanks H20.
    Boating is nothing like cocaine, boating is much more addictive and results in bigger parties!

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