Carburation in the mountains or at higher elevations

[Bill Stoneberg]

I live at sea level or as close to it as possible without getting wet. My Riviera that I plan on driving to Seattle was bought here in Texas and is jetted for the lack of altitude we have here.

My question is, am I going to run into problems once I get into the mountains that are on the way between Texas and Seattle ? Its been a while since I drove a carburated car in the mountains and if I remember correctly, my 62 Chevy had pretty poor response and no top end. How will the Carter AFB handle this ?

Would it make sense to take a different set of jets with me ? I will stay mainly on the interstates but we have a couple of side trips planned.

What about overheating ? Will I have an issue with this too ?

[Mark Shaw]

Your Riviera has plenty of power, so a slight loss due to thin air should not be enough of a problem to warrant replacement jets.....unless you are towing a trailer, etc.

[NTX5467]

Bill, generally, one jet size smaller for each 1000ft of elevation change from sea level. As in SL = .089" 2000' = .087" Or . . . you can kick in a little more initial timing (i.e., about 2 degrees BTDC) and accomplish about the same thing. This used to be the typical rule of thumb for "fixed jet" carburetors, whereas what the Carter AFB, AVS, and ThermoQuad, along with Rochester QuadraJet spreadbore, are "metering rod" carburetors.

With your Carter AFB (which is the OEM version of what Carter sold as their aftermarket AFBs, and what the current Edelbrock AFBs are descended from), it's easy to change the primary metering rods rather than having to get all involved with changing jets (and pulling the top off of the carb to do so). What used to be called "Carter AFB Strip Kit" (with a variety of primary metering rods and jets, plus some secondary-side jets) is now sold as the Edelbrock tuning kit. For general information, you can download that instruction manual from the Edelbrock website.

Still, I think you'll be fine with what you've got now. The AFB is a nicely tolerant carburetor whose fuel metering is done by metering rods acting against manifold vacuum, which is resisted by a spring under each power piston. I suspect that as the altitude decreases and manifold vacuum similarly decreases slightly, the metering rod carburetor that works well and is calibrated for (generally) sea level will probably only need the next-weakest power piston spring to maintain performance at the higher altitudes. You'll probably also notice that fuel in those higher elevations has a little less posted octane than at sea level.

Any information about a caravan from the TX Coast???

Enjoy!

NTX5467

[Bill Stoneberg]

Willis, the only way there will be a convoy is if some of your folks go.

I am going and thaking Pete, and Willie is going. We will probably meet on the road somewhere but we have different schedules and driving styles so we dont drive together.

Is anyone from your chapter driving up there ?

[NTX5467]

At the last meeting, there were several that indicated they were going, but I don't recall specifically who they were--just a show of hands.

I just recalled some mention of possibly renting a car hauler (or similar) to take cars up there or mention of a "convoy" (I guess now you'd have high-powered Family Channel radios rather than CBs???). I was just wondering where things were in that regard . . .

Thanks,

NTX5467

[carbking]

Bill - Carter changed metering rods on the primary side for high altitude using the AFB carbs; not jets. Since the effective metering area of the primary is the diameter of the jet less the diameter of the rod AT A SPECIFIC VACUUM; changing the jet will change the metering percentages at high and low vacuum at a different rate.

Standard calibration is sea level to 4000 feet.

One size lean is 4001 to 6000 feet.

Two sizes lean is 6001 to 7000 feet.

If you are just "driving through", probably leave it alone (carry a spare set of spark plugs if you wish). If you are relocating to an altitude above 4000 feet, give some consideration to recalibrating the carburetor.

CAVIAT!!! BE VERY CAREFUL OF CHANGING RODS WITHOUT GOOD INFORMATION. THERE ARE AT LEAST SIX (6) DIFFERENT ROD CONFIGUATIONS (LENGTH) FOR THE CARTER AFB! NONE of the aftermarket rods which were in the later Carter "Strip kits" were applicable to your Buick carburetor!

If you are relocating, and wish to recalibrate the carburetor; you need to know the following:

(A) average altitude where you will do most of your driving.

( stock rod dimensions (base, high vacuum, mid-range if used, low vacuum diameters, steps, and lead-ins)

© percentage desired decrease in fuel metering (you should also take in to account deathanol, if it will be used).

Jon.

[imported_buick5563]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Any information about a caravan from the TX Coast???

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Willis,

I can't make the drive this year due to the distance. I just don't get that much vacation time (even though I would probably make it in two or three days <img src="http://forums.aaca.org/images/graemlins/wink.gif" alt="" />). I'm still trying to figure flights, but at this point, even that is looking iffy. <img src="http://forums.aaca.org/images/graemlins/frown.gif" alt="" />

Leadfoot

[Centurion]

Bill, I can confirm what others have said. Many of us who drove from Seattle to Flint in 2003 were driving nailhead Buicks with Carter carburetors. None of us re-jetted our carbs, and we all did fine crossing the Continental Divide. No one experienced problems of this kind. In fact, 95% of all problems experienced by our large group were tire-related. Some folks had older radial tires on their cars, and they quickly experienced belt separation problems on the first day out. With tires replaced, it was clear sailing. One guy lost a water pump in a '65 Riviera, and I had to replace front wheel bearings in my '59 (alignment shop had over-torqued front bearings). No one was significantly delayed.