Carbureted engine struggled/died at 3500 ft off-roading

[HoldMyPocket]

I have a modified Holley 600 CFM with non-adjustable floats. The guy who built it installed a vent-tube like the Truck Avenger, and pretty much built it for my vehicle. (Built 302, c4, 35's, 3.50 gearing, lifted, locked, mostly a daily driver at sea-level with occasional off-road trips from San Diego to maybe as high as Big Bear).

I was up at about 2,500 feet on a trip, and started heading up a nice incline which took me to around 3,500 feet in what seemed like a mile. Any time I hit any steeper sections in the road, or let my foot off the gas the engine wanted to/did die. I ended up turning around and could tell things got significantly better as I headed back down the 1,000 foot incline and played around at the lower altitude.

Apart from this trip, when just driving around at sea-level on the street, if I slow down suddenly and take a sharp turn my engine sometimes stumbles/wants to die if I don't get back on the gas right away.

The question is, do I need to re-jet before I go on these trips or during? Do I just carry a jet-kit and increase my jet size for every 3,000 feet when heading up a mountain or is the altitude range broader than that? What's the quickest way to do this on a trip? Also, can anyone reccomend a good book or website for understanding Holley carbs?

 

[73azbronco]

I'd hook a fuel pressure gauge up first and see if its getting fuel,then start with the carb. Might also check timing.

 

[DuctTape]

The question is, do I need to re-jet before I go on these trips or during? Do I just carry a jet-kit and increase my jet size for every 3,000 feet when heading up a mountain or is the altitude range broader than that? What's the quickest way to do this on a trip? Also, can anyone reccomend a good book or website for understanding Holley carbs?

I run edelbrock, so can't help with Holley (did you try their website? Edelbrock has a great manual). Edelbrock has a quick change rod system wherein it literally takes 5 minutes to go richer or leaner, albeit sort of a rough adjustment (finer adjustments require jet change). Not sure if your carb had same feature but manual should tell you.

I will say that I've run two stages too rich (and two stages too lean) and it still runs. Runs rough but doesn't stop. The going around the corner problem might be dirty carb, carb bowl, or something in your tank pickup. Good idea to verify your fuel pump but I'd guess given that inclines and corners cause problems it is more likely something that is gravity and force vector based rather than fuel pump failure.

 

[stock1970]

I just lean my carb up and it does fine. maybe set your idle a little higher also could help.

 

[jamesf7278]

if your just driving around corners and it wants to die I would say float level? I don't know what non adjustable ones are, I would think I would want them to be?. explains the steep angle driving stalling aswell.

 

[TwoDalesDad]

I would change out that holley carb....go EFI....or go home.....and work on your holley.....

 

[HoldMyPocket]

I would change out that holley carb....go EFI....or go home.....and work on your holley.....

Don't remember asking that.

The non-adjustable floats just means they're not that easily adjustable.

I guess I just needed to know what the range is before I start changing jets. Sounds like I'm right at the biggest jet for sea-level and could probably go down a size or two so I don't have to mess with them just to go up to the local mountains.

 

[SHX669]

Float level - even the Circle track Holleys have a different float/extended jet configuration.
I'm not a holley expert but i 've never seen one with" non adjustable floats".
That's one of the things I like about them - easy to adjust the float level.
SHX

 

[jamesf7278]

I had a 70 440 cuda a few years ago, it had a holley 750 vac secondary carb on it, didn't like corners or stops either so I took the carb off and rebuilt it and adjusted the floats to have a hair more fuel in the bowls and it worked great after that. they are very easy to work on, problem is you always have to work on them

sweet looking rig btw!

 

[08ag]

The COMMON thing to do with carbed engines ascending into altitude is lean the jets out. Next time you head up, I would recommend dropping 2 numbers on the primary jet. You probably will never use the secondaries. About the 4,000 ft mark is where jetting is beginning to be required.

The off camber and steep angles would only compound the initial problem (too rich). Higher altitude = less oxygen

 

[jckkys]

HPBooks Holley Carburetors & Manifolds or S-A Design Holley Rebuilding & Modifying are good sources of info on Holleys. The so called non-adjustable floats are adjusted by bending a tab on the float like most all other carbs. It just can't be adjusted with the carb assembled.
The float level is normally lowered by 1/6" to 1/8" or that much below the sight plug threads to to reduce angularity issues on off road vehicles. It sounds like you are a lot more than a couple sizes too rich. I've driven over the San Diego Mtns. or about 4300 ft. with a Holley and no problems. The jets were the same as I run in Tucson at 2000' or El Centro below sea level.

 

[PaveBronco]

Living in Albuquerque NM which is already at 5000ft and wheeling up to 10,000ft, I’d set my Holly to run just a little lean in town which worked fine up high, a little timing change helped also. An adjustable fuel pressure regulator helped with the fuel in the bowls, but sounds like you need to adjust your floats for sure. I ran an Edelbrock for a few years because they are quick to change the metering rods, but they just don’t work well off road, or at least I couldn’t get mine to work. Also the higher you go the less air pressure so the easier it is to get into a vapor lock situation.

 

[SHX669]

I've had my current Holley equipped Bronco from sea level { as in " look out for the salt water"} to 4000+ elevation with no issues or rejetting. Had several carbed rigs with Holleys that I took from the surf to 5700+ feet for a week at a time and didn't notice anything of concern.
But if I was going to move to that elevation or spend the summer there I would certainly have rejetted.
SHX

 

[Rustytruck]

As stated above, reset the floats dieing on the street is a good sign that is an issue. High float levels will make much higher fuel flow in the transition levels and gets worse at elevation. can make it run rich at part throttle. I would check the fuel pressure as high pressure forces more fuel in the chambers on every bounce over flowing the float chambers and dumping fuel down the carb. you might have to go old school and use a pressure regulator set around 3 lbs when off road. off road you dont draw as much fuel as driving down the freeway. Another thing to check is the power valve make sure its not leaking or the wrong one for running at altitude. At 2500 feet you shouldn't be having these problems.

 

[Timmy390]

The float level is normally lowered by 1/6" to 1/8" or that much below the sight plug threads to to reduce angularity issues on off road vehicles.

If this is the case, then I'll say it's not so much the carb but the GREARS. 3.50's with 35? I had my foot to the floor all the time trying to maintain speed with 3.50's and 32's.

My guess is, carb is going dry due to the amount of foot you have in it. Add some altitude and it makes things worse.

it explains the corners too.

You need more fuel in the carb.

Tim

 

[Naughty Bronc]

I did not read all the replies but your fuel mixture is fine at lower elevation but it will run rich at higher elevation. Generally here in Mt ill tune the carb at higher elevation and when i get to lower elevation it leans out but not enough to do any damage. Plugs still look great.

Also your float level needs to be just at the bottom of the sight window. those need to be adjusted first before adjusting your fuel mixture.

 

[jckkys]

The recommendation to lower the float level comes from Holley. Edelbrock makes the same recommendation for AFBs This small change in fuel-float level isn't noticeable in terms of running leaner it just reduces the chance of fuel spill over. An engine dying from a lean condition as a result of climbing to a higher altitude isn't likely. Higher altitude means less oxygen so less fuel can burn efficiently. The fuel pressure from the mechanical pump is not enough to flood the engine but is plenty enough to adequately feed any small block.
If the timing was way off it wouldn't run well at low altitude. If the engine is lugging because of a high load at low RPM, the power valve opens aggravating the over rich condition.