Howdy folks,

Well I finally have my truck running after a full engine rebuild. Its a 59 292 bored.060 with a mummert aluminum intake and headers. It has a mild cam. 
My question is I had it over carbed I think with a 625 street demon carb. So the engine builder recommended a edelbrock 1403 500cfm carb with a 1" open plenum spacer. I live in Longmont CO and we are 4,984 feet above sea level. Anyone out there live in co and tune this carb for a y-block. I have tried every different spring and the strongest ones ( silver ) seem to work best. For the jets Edelbrock recommended 83 jet for primary and 92 for secondary. I tried several different metering rods and the stocks 6552 seem to be ok. The truck seems to have a small bit of lag when you really get into it. Its not a stumble but the pick up i not instantaneous. Any other tuning hits would help tons. Thanks folks.

From the manual that should have come with the carb. It's available online if you need to print one.


"High Altitude
Altitude has a direct effect on the operation of most carburetors. As the altitude increases, the air becomes less dense so a carburetor, originally calibrated at low altitude, delivers too much fuel and the engine runs richer. If the preceding tuning procedure is performed on an Edelbrock Performer Series carburetor, a proper high altitude calibration will result. If the vehicle was calibrated at lower altitude, however, and is to be driven at high altitude temporarily, it is not necessary to repeat the complete calibration procedure. Instead, use the rule of: “2% leaner per 1500 feet” and the Calibration Reference Chart for your model carburetor. For example, with a #1405 at baseline calibration (location #1 on the chart) and intended operation
at 6000 ft. altitude, you would want 6000 divided by 1500 x 2% = 8% leaner calibration. That would be location #24 on the chart which would require only a rod and jet change."

The manual is pretty dry reading and at first seems confusing, but if you stay after it it makes sense. They show a little larger jets in the chart, so maybe you've already made the altitude adjustment. You might also search spacers here. I think an open spacer might not be optimum for your motor, but someone who really knows will chime in.


miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Hi Miker, thanks for the reply. I am looking at the chart now for a 1403 and the #24 location I believe is asking for only a rod change. Am I reading this wrong? here is the link to my chart. http://www.edelbrock.com/automotive/misc/tech-center/install/1000/1404_manual.pdf

Yes, but I read ref#24 as being a 86 jet, not the 83 you're running. It's a bit confusing as the first jet chart starts at 1404, but later charts list 1403/1404 as the same. On the surface, it appears Edelbrock has made a recommendation different from the tuning manual.

If you're running an 83 jet, and the rod change for altitude as shown in ref#24, you're lean. You also need to know what your vacumn reading are at part throttle cruise at speed. If your base setting is lean, then the natural color spring at 8" will be opening the power circuit and help compensate for it. But until you know the vacumn reading at idle, light cruise, and (call it) highway cruise, you don't know when your running on the enrichment circuit (power valve open in Holley terms).

I don't have enough high altitude experience to know the effect on timing, but that will be another area to explore. I've got an old friend who does a lot of bracket racing, and he has years of data for each engine combination he's run. Tuning for density altitude based on atmospheric pressure and temperature is really a black art in his league. Uncorked, no throttle stops, he runs mid 9's on a cool day at sea level. This is to run a 10.7 bracket at altitude on a 100+ degree day.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Try a 4-hole or divided spacer.  Open is generally not the best choice for street use.



Lawrenceville, GA

I do have an extra 4 hole spacer however its really tall about 3" I think. Is that bad or good? I can hit napa tomorrow and get whatever height would be best in a 4 hole spacer. Thoughts? I am still also confused on what springs jets and metering rods I should be running.

1", 2", maybe even your 3" will be ok, if you can fit it under the hood.



Lawrenceville, GA

Here's some background from Ted's site. Big motor,but the principles apply. See what clears the hood, and mind Edelbrocks warnings about air cleaner sizes and clearances. It's in the tuning manual.

http://www.eatonbalancing.com/blog/2012/09/29/carburetor-spacer-testing/

I'll stand by my comments about you needing to know the vacumn readings.

The Mummert manifold and headers would normally like a little richer mixture than stock. That's a generic comment about any engine with those upgrades.



That said, you need to sort out why you've got the smaller jets (how did Edelbrock recommend those?) than the base carb info and tuning chart show. If you didn't start stock, I'd be inclined to install the stock jets, rods, and springs in the primary. Since you don't mention the secondary's I'll assume they haven't changed. My experience with these carbs is on almost any moderate street motor, they're close out of the box. Tuning is relatively minor for drivability or max power. Then check the float settings. From your description, I don't think you've got a fuel pressure problem, but that's also a possibility. Check the timing, vacumn advance disconnected and plugged. Most of these motors like more initial than the book, up around 10 degrees initial, with 25-30 all in by 2500 or so. I'm assuming you've got the stock distributor, and someone didn't put a Loadomatic in it. They won't work at all with that carb. We could go on about a PCV system and the right valve, etc. but you seem too close for that.

From there, I'd tune for drivability, and follow the chart. You're at 5000 ft, so you're not going to move all the way to ref#24, just part of it. Maybe, depending on the cam, not at all. One change at a time. Watch the ambient temperature if you have big swings. A result in the morning at 50 degrees may not translate to late afternoon at 90. Keep looking at the tuning manual till you really understand it. I've been wrenching on cars for 50 years. Most of my dead ends were from not reading the instructions. Not just cars, either.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

MIker. To my knowledge Edelbrock recommended the smaller jets because of my elevation here in Colorado which 4,984′. the jets the recommended and that I have in the carb now are 83 primary and 92 secondaries. I was told to leave the rods as the were which i believe are 6554. My vacuum at idle is around 7. I have had the best luck with the strongest ( silver ) springs. I have a completely rebuilt t-98 4 speed for trans. And the original dizzy however I did put the pertronix in place of the points.