6 in a row makes it go? But at 5k ft elevation?

[mattbert56]

Well I'm sure there are many threads of carb stuff for inlines, but wondering if anyone that lives in higher elevations has any input. I've got a 1406 edelbrock on an offy intake and long downtime headers. Stock cam. .20 overbore. Rest of the engine is stock. I cannot seem to lean it out enough for it to run reliably, being at 5k foot and only seeming to drive it in higher elevations. (The mountains) I'm wondering if downsizing the jets to the sizing of an edelbrock 500 would be beneficial? About 70 bucks give or take, or switching to a 390 Holley? The carb that's on it really has treated me well up till now. Little situation backstory. Truck was moved from sea level fo where I live now in Wyoming. Different air. Thinner. Ha less of it. Any input would be rad. Thanks.

[chevy_mike]

When I had my '64 Chevy II wagon, it had a 250 L6 engine with Clifford intake and headers running a Holly 390 carb. It ran really well setup for my under 500 ft elevation but we would take it up to local mountains for shows or cruises up to 6500 ft and it still ran well. Sure a little less power but that was expected at higher elevations. If you jetted it for that elevation, I am sure it would do much better than trying to get a large cfm carb to run lean enough.

Honestly, a 600 cfm carb (1406) is way too much carb. Even the 500 cfm is typically too much unless you got some performance tricks. In everything I researched and my experience, the 390 cfm Holley is about perfect for the inline 6's.

That's my input.

[mattbert56]

Chevy_mike.

Appreciate the input initially I wanted to run a 390. But this 600 fell in my lap. It seemed to run fair when it was in cali. Little rich but I never hot roses it to hard. These old 4x4s can be a bear to fix &find parts for. Ha. I think the 600 was right on the cusp of being acceptable for 292 ish cubic inches ha. The gain in elevation must have been the tipping point.

[vince1]

These days when almost every new car has a turbo maybe you could find one in a junkyard?

[mattbert56]

Perhaps. Our junk yards out here are really pretty crummy. They want alot for junk. And any yards worth a hoot are a few hours drive. If I where to swap to a 390. I'd try and sell the 600 and just buy it new. *shrug*

[SkinnyG]

Lower the float maybe 1/8" or so at a time?

Should lean -everything- out enough.

[mattbert56]

Originally Posted by SkinnyG

Lower the float maybe 1/8" or so at a time?

Should lean -everything- out enough.

How would I do that on a 1406? I was looking at metering rods and jets from a 500. I think the main jets are .100 on a 600. And the are .89 on a 500. Dont quote me on the exact numbers. But I belive it was a substantial difference. I'm not very sabby with carb tuning. I got lucky when I out it on initially. It didnt need to be messed with much. Just fuel air screws. And idle.

[SkinnyG]

Float adjustment can do some fine-tuning of mixture, and I'd totally try that on your 1406.

I did a quick Google and came up with this:

Edelbrock Float Adjustment - YouTube

[mattbert56]

Right on! I really havent had much time to dig into it lately. Been busy with 2 other projects eating up my time befor summer. .

[61K10]

hay Matt! Hows the cold country treating you? So how it running hot and cold? Black smoke? Plugs black? Timing? Good coil? Need more info guy.

Kimble----------

[mattbert56]

Originally Posted by 61K10

hay Matt! Hows the cold country treating you? So how it running hot and cold? Black smoke? Plugs black? Timing? Good coil? Need more info guy.

Kimble----------

Haaa! Hey kimble, yeah shes not much if a runner when its -24 gave her the old college try tho. Wasent havin it. One thing I will have to change all my gear case oil to somthing thinner than 85-140 hahahah felt like my trans was full of grease. I belive the timing is still at 8 degrees advanced. Havent checked plugs coil is good. Itll start and run occasionally but not reliably. Floods with little to no effort. I was going to try taller air filter and smaller jets since that's the cheapest option over replacing with a smaller doodad carb. How is Sierra life? It's just starting to warm up here. Had a high of 58 the other day that had me in shorts and a t shirt

[Steeveedee]

You can buy a kit like this https://www.ebay.com/p/Carburetor-Ca...8024119&chn=ps and tune the 1406 to run at your elevation. It comes with a CD that details how to do the tuning. I bought one when I put a 1406 on my 305 Chevy engine, but sold it with the carb when I put a Q-Jet on it.

The 600 CFM would only be an issue if you got into the secondaries, and they rely on flow in the engine, so probably wouldn't even open the secondary air valve if the vacuum is low enough. Low here meaning that manifold vacuum is closer to atmospheric pressure.

[mattbert56]

Originally Posted by Steeveedee

You can buy a kit like this https://www.ebay.com/p/Carburetor-Ca...8024119&chn=ps and tune the 1406 to run at your elevation. It comes with a CD that details how to do the tuning. I bought one when I put a 1406 on my 305 Chevy engine, but sold it with the carb when I put a Q-Jet on it.

The 600 CFM would only be an issue if you got into the secondaries, and they rely on flow in the engine, so probably wouldn't even open the secondary air valve if the vacuum is low enough. Low here meaning that manifold vacuum is closer to atmospheric pressure.

I'll have to check that out. It seems like those kits are much cheaper than the brand name kit by edelbrock. I think they call it a performance tuning kit. Once its warmed up it doesn't seem to be to picky. But when it's cold it always need help starting

[SkinnyG]

If you need to pump it a bunch to get it to start, you might just need the choke adjusted. They're finicky because you really only get one cold start per day out of it to test and adjust.

If you need to hold the pedal down to flood clear it, then the choke still may need adjustment or it might be jetted too rich.

The Q-jet on my '77 was built following Cliff Ruggles' recommendation in his Rochester book, including setting the float level at 1/4". I put up with this for four years trusting that he knew what he was doing. I needed very little choke to start it (and it started perfect every day all through Canadian winters), but EVERY re-start was a flood clear as it would boil the fuel in the bowl and flood the engine every time I parked it. Even the mixture screws - 1/32 of a turn either way would be so rich it stumbled on tip-in, or was so lean it would diesel at shut-down.

I recently set the float back to factory specs and holy carp (15/32" float level) - this thing is awesome. All manner of evil is gone.

Right now, adjusting the float level is a free and reversible modification, while you wait for the tuning kit to come in.

[61K10]

Make sure your choke is not all the way closed when cold. This should be in the engine-drive train forum. some good info there.

[jayoldschool]

As others have pointed out... the 1406 is too much carb. That's the right carb for a 350. I actually have the slightly richer-jetted 1405 manual choke on my 71 350 (and wish I would have bought a 1406 back when I could barely afford the manual choke 1405, I was young, lol)