Carb at high elevation

[85_Ranger4x4]

I have old memories of driving across the USA on fairly new and under construction interstates while burning leaded gas. Slight and not so slight "rolling coal" seen from tailpipes when hitting the Rockies. I saw drivers removing air filters and other methods to try to lean.

What spot and JaSAn said. You can tune way too lean and enrich by using a manual choke, like I’ve seen done with a lot of too lean small engines. Decades ago, Edelbrock’s were avoided for mainly Holleys because of a lack of understanding how to tune. Again, what spot said.

Before gasohol, I drove to the Rockies with no modifications, but the spark plugs and tailpipe showed slightly rich and probably not good for piston ring/cylinder wear. Now, with gasohol, the boiling point is so low it can actually boil the fuel out of the bowl with long pulls, parked or long idling. Also vapor lock. Electric pump helps, along with fuel line heat sleeves.

One crude method I’ve seen is to allow air to enter under vacuum, not through the venturis, to lean the mixture. Leaving a carb's ported vacuum fitting open can allow idling, yet also allow extra air into the manifold above idle. I’m so old, I remember removing the vacuum line from a windshield wiper motor to lean the mixture.

If not enough to correct the over richness, a manifold port can sometimes move more air. Under a really hard pull, vacuum can decrease to the point not much air can bypass the venturis for leaning.

I don't want to curse like others about the somewhat like fuel injection Variable Venturi carbs on USA vehicles around 1980, and I had good luck with the mainly British styles with the oil-filled reservoir. Fords variable venturi carbs worked great on V8 engines if looked after. They can still be had. So can a 4 to 2 barrel adapter plate.

ford variable venturi carburetor for sale - Google Search

Ford V8 flathead carbs had two drain plugs facing forward in the fuel bowl. Remove them, loosen the jets through the holes, then use a holding screwdriver to remove and replace the jets. Handy. Picture below. I installed one on a 2300 Ranger years ago using an adapter, to replace a gummed up emissions model that looked like a porcupine. Worked great.

Holley has a quick change jet kit for center hung floats, but at some expense.

Excuse the rambling. I’ll never forget my first coast-to-coast trip. Good luck.

On that note I did find this which is interesting.

The Carb Cheater

Helping people tune their carburetors

www.thecarbcheater.com

Kind of reminds me of the metering system my original feedback carb had to adjust the mixture.

But with modern parts rather than a bunch of 40yo obsolete stuff that barely worked when new.

And if anything goes sideways with it... a vacuum cap and it is business as normal with my carb, a ECM laying down won't strand me.

Not as good as EFI especially for off camber stuff (which I really haven't had an issue with)... but worthy of investigation.

Took our new Mercury Zephyr on vacation in 1983 out west to see the sights, coming back thru Colorado near Vail it wasn't running well. I tightened down the idle screw on the one barrel, when I got past Denver richened it up again.

Higher altitude, less air - maintain the 14:1 ratio by leaning it out slightly. Going back to sea level, richen it. That's all we did in those days - matched the ratio to the amount of available air. Less air, less fuel.

EFI is considered the fix for the issue yet I have heard the Denver area and other higher altitude metros get a different tune program which handles things with more finesse. What none of this does is fix it when you have mountain sickness - and you can't fly with your own bottle of O2 to help, nope, not allowed. But you can buy your own tank and mask to help if driving. It addresses the other side of the ratio - it supplies more O2.

If someone is just passing thru quickly then a very low metered shot of NO2 could be a solution. But, I wouldn't strap that tank on the roof either. This is where a supercharger/turbo could help - pump more air in - which is exactly why they were installed on fighter planes in WWII. A properly controlled fuel delivery system for compressed intake air meters that amount to directly meet ratio needs.

None of this is cheap.

And I am about the only one in the group with a NA engine... and the only one with a carb at all.

Boost is not on the table for this old engine lol, not sure it would really address my A/F carb issue either.

12k is like the max, it isn't going to be sustained there.

 

[burleyman]

Thanks for the link to the carb cheater. I thoroughly enjoyed the video, and learned a lot. I have carbs, but no dramatic altitude changes.

The non-metallic air bleed plate used could help keep heat away from the carb, also. I've had good luck with a short piece of fuel line with a screw inserted for vacuum caps.

I did try using exhaust gas temperature and a finger operated valve in the line years ago, but not for altitude changes. Automatic finger cheater, great idea. I don't think he said anything about better gas mileage.

I sometimes wish my early EEC-IV simple EFI 5.8L Ford was carb equipped. For emergencies, I have a spare ECU, distributor, ignition module, throttle position sensor, MAP sensor, and special code reader. Dropping the tank to replace the in tank fuel pump is a chore. If a truck instead of a van, there would be a hole cut in the bed.

I know which system suits me best broken down somewhere if you don't mind dirty hands and fingernails. That goes back to what you said about the wall of parts.

The Ford variable vacuum carbs, especially the ones with the metal venturi blocks, do a good job with altitude changes. They are a sideways version somewhat like your Edelbrock, except movements and positions are controlled by vacuum instead of directly by your foot. They depend upon a rubber diaphragm to move the venturis. Sort of a MAP sensor.

 

[85_Ranger4x4]

I have a fairly thick phenolic spacer, a edelbeock will not tolerate being too close to the intake. Fuel boils out of the bowls when you shut it off and floods it very quick without a spacer.

I have heard stories about the vv carbs (mainly horror stories), I really ought to check into them if for no other reason just to see how they work.

The PO of my truck was a believer of the bolt in a hose for plugs. He must have thought it sucked pretty bad, I still laugh that most were grade 8

 

[craig333]

Very easy to change the jets on my Solex. It's just the gas that leaks out onto the manifold thats a bit disconcerting!

 

[ntsqd]

No matter what, an NA engine is going to feel the altitude. If you let a turbo engine spool down it too will feel the altitude until you manage to get it to spool back up. BT, DT.

That said I've had my old '91 Suburban from -281' (Badwater) to 12,400' (Barcroft Station) and it's TBI system was able to compensate. I would give some serious thought to a GM TBI system, particularly one based on all GM parts, so long as you're under ~300HP output. Above that you you start to really push the system beyond it's design envelope. Pared down these systems are pretty simple and don't need a lot of sensors etc. As EFI computers go, they're not very smart, but they're smart enough. Howell used to and may still sell complete kits with proprietary tuning, but you can put one together in a JY. If you find a 305cid donor then it should be pretty close right out of the donor.

I REALLY don't like any of the aftermarket EFI systems. At least not until you get into Motec and similar territory. I'm not seeing that kind of cash floating around. Much below that and they don't even know what "MTBF" means, much less have any idea of how their parts would rate. OEM EFI has to be durable and reliable in ways that the common aftermarket EFI's can't match.