Moved to New Mexico...runs like crap

[Chief Master Sergeant]

I can barely keep this thing running. Do I need to gap the spark plugs differently here? I assume, because we're at a higher elevation, that the carb needs adjusting as well.

 

[broncopete78]

Thinner air due to the elevation change will defiantly make you run rich and fowl plugs. Plug gaps should stay the same.

 

[cldonley]

On small aircraft engines, the difference is enough to generate a 250 rpm idle speed change in Denver. So you will definitely need some carb adjusting, small jets perhaps.

 

[DirtDonk]

You can temporarily test that theory (it's a very accurate theory though!) by creating a semi-controlled vacuum leak.

Either open up a small tube/port in your existing setup, or replace your PCV with the wrong one from another engine, or literally install an adjustable valve you can open and close into one of the vacuum lines.

A good "wrong" PCV valve would be one from a mid-seventies Ford Granada w/302.
The one I used had a 90 degree fitting, instead of the stock straight up version of a stock Bronco.

Give it a shot and see what changes.
It's definitely not the same as changing your main jets to smaller ones, but it's a reasonable mimic of that.

Paul

 

[broncnaz]

Should be able to advance the timing some and Tune the idle mixture. Jetting may need some tweaking but Id getting it running better first.
Wouldnt really bother with the other suggestions unless you run out of adjustments which you shouldnt its not like you went from sea level to 20,000ft. Even if you do run out of adjustment then something is wrong with the carb.

 

[AZ73]

Should be able to advance the timing some and Tune the idle mixture. Jetting may need some tweaking but Id getting it running better first.
Wouldnt really bother with the other suggestions unless you run out of adjustments which you shouldnt its not like you went from sea level to 20,000ft. Even if you do run out of adjustment then something is wrong with the carb.

Back in the day mechanics on the east and west side at the start of the rockies made a good living adjusting the timing and the fuel needle valve for the ride over the rockies. I used to pay $20 in the 70's every time I went up and came down until I bought a timing light.

 

[Pa PITT]

.. I'm going to subscribe to this thread .
.. SO Chief when did you move & where to.
..Reason I want to follow is because we go hunting every year in New Mexico . My Bronco just plain quit when I took it to 7250 ft from about 1200. We loaded it onto the trailer & brought it home .It set while I was sick for a week. but I was going out trying to start it every few day. Then it just fired up like nothing was ever wrong. I never found out what was wrong with mine . It rans another year or 2 and I swapped it over to the Diesel.
.... Running Buddies has always ran crappy when we get up to the hunting spot but it has managed to keep going. We had the same trouble with his 6 cyl & then the V8 Np435 & then when it was swapped over to the AOD & another 84 carb. It always runs nasty up at 5000 plus .
... Now he's got it in the shop for Fuel Injection motor swap. I don't think it'll get done before we go this year .
... So Chief it may be time for you to swap to Injection.

 

[rguest3]

Use a Vacuum tuning gauge hooked up to Full Vacuum on carb or intake manifold to tune for highest vacuum readings.

Re-set idle mixture screws - Set to achieve highest vacuum reading. Afterwards you may have to adjust curb Idle screw as well.

Advance Timing - Set to achieve highest vacuum reading. May have to back off advance a little if engine pings under load.

This should cure most problems assuming plugs, wires and distributor are in good shape. Check plugs after some driving time to see if too rich. Next step is smaller jets, if needed, at 2 size increments at a time.

 

[MarsChariot]

You probably need to go with smaller main jets. ON the stock 2100 we use to use 49s or 48s. I believe the stock was something like 52. It depends on what carb you have. I am running a autolite 4100 with 49s (I think) on the 76 and it runs clean to 11,000 feet.

The other thing is the license plate. If you still have that Tejana plate you will be needing to get rid of that plenty quick. The New Mexico automotive gods can tell these things.

 

[jim3326]

The other thing is the license plate. If you still have that Tejana plate you will be needing to get rid of that plenty quick. The New Mexico automotive gods can tell these things.

That's funny right there Mars;D;D

He's running a Quadrajet. I will get in touch with some of my racin buddies that are pretty good with the jetting. They all left town this weekend but I will let you know.

Jim W.

 

[Chief Master Sergeant]

.. I'm going to subscribe to this thread .
.. SO Chief when did you move & where to.
..Reason I want to follow is because we go hunting every year in New Mexico . My Bronco just plain quit when I took it to 7250 ft from about 1200. We loaded it onto the trailer & brought it home .It set while I was sick for a week. but I was going out trying to start it every few day. Then it just fired up like nothing was ever wrong. I never found out what was wrong with mine . It rans another year or 2 and I swapped it over to the Diesel.
.... Running Buddies has always ran crappy when we get up to the hunting spot but it has managed to keep going. We had the same trouble with his 6 cyl & then the V8 Np435 & then when it was swapped over to the AOD & another 84 carb. It always runs nasty up at 5000 plus .
... Now he's got it in the shop for Fuel Injection motor swap. I don't think it'll get done before we go this year .
... So Chief it may be time for you to swap to Injection.

I moved to Albuquerque late last month.

You probably need to go with smaller main jets. ON the stock 2100 we use to use 49s or 48s. I believe the stock was something like 52. It depends on what carb you have. I am running a autolite 4100 with 49s (I think) on the 76 and it runs clean to 11,000 feet.

The other thing is the license plate. If you still have that Tejana plate you will be needing to get rid of that plenty quick. The New Mexico automotive gods can tell these things.

I'm registered in Alaska. ;D Yeah, like Jim said, I am running a Quadrajet. Tried to go by the Auto Skills Center here on base today, but they were closed.

 

[broncnaz]

The qjunk may not need a jet change as the metering rods kinda serve the purpose of smaller jets lower vacuum and the rods will stay farther down in the jet longer. Work on the idle then run it for awhile then check your overall jetting.

 

[Rustytruck]

On the Quadrajet raise your idle screw up to 1000 rpm then take you mixture screws and screw them in to lower the idle back down to 800 rpm or so.
Raising the idle screw lets more air in past the butterflys at idle and leaning the mixture screw takes extra fuel out. Make sure you also use a vacuum guage to get the highest vacuum reading with a steady needle. I run from 0 to 8000 feet without jet changes but at 8000 feet you know it needs it. Running at higher elevation I would also reset your float level. You dont want a high float level on a Quadrajet it effects the fuel rate as the carb transitions off idle.

 

[Chief Master Sergeant]

Unfortunately I wasn't able to bring the majority of my tools with me. Going to have to wait for Jim and friends this weekend. No worries though.

 

[Chief Master Sergeant]

Thanks to Jim and his bud I got it running half way decent. The carb needs to be rebuilt in a bad way, but she gets around. Thanks Jim!

 

[sprdv1]

Glad to hear it Chuck..

Hope everything else with the move went well.

 

[John Marinan]

I had two APT carbs rebuilt by Chuck Sterling for high altitude use. one for a 350 chevy and one for the Bronco. They work perfectly all the way to 13,600 ft. PM me your email and I can forward you a note from Chuck describing exactly what he did. You can also contact him at chuckster60951@yahoo.com he charged me $150. Cliff Ruggles can also build your carb but he is usually very busy.