I'd asked a lot of questions a couple of months ago, then dropped off for a while (first for a wheeling trip, then for cancer surgery - on me, the jeep bodywork comes next ;-) )
Thought it might be of use to someone to relate my experiences setting up an Edelbrock 4bbl carb on my V6-225 – warning, long…
Background: In bringing my ’66 back from a long sleep, it became clear an engine re-man was in the cards (145K miles, valves acting up on un-leaded gas, etc.). I had the engine sent off to Jasper (magnafluxed the block, .040 over, RV cam, etc.). Unfortunately the original intake manifold was apparently warped. Even after a light pass at a machine shop, we couldn’t get it to seal up, and could not find a replacement 2bbl manifold. So, I ended up with an Offenhauser 4 bbl. intake manifold (dual port, dual plane). The smallest carb we could find was the Holley 390 cfm, but after 2-3 months of messing with it, including 2 pro 4x4 shops here in northern Colorado, I could not get it running well. I swapped the Holley back out for an Edelbrock (model EPS 1404, 500 cfm, elec. choke), which out-of-the box ran better than we ever got the Holley.
I live at about 5000’, and mostly go up from there, so no surprise that even though the engine ran pretty smoothly, it was way rich. Edelbrock carbs (http://www.edelbrock.com/automotive/index.html) use both metering rod and jet changes as needed to calibrate. I had a big trip coming up (a week of wheeling in the Colorado high country!) very shortly after getting the carb in, so we took a guess at 3 steps lean (we would be above 12,000’ on at least a couple of trails). Incidentally, Edelbrock recommends 1 step (4%) change in mix with every 3000’ elevation change.
Stock setup (sealevel) for the carb is .086 main jets, .065 (cruise) x .052 (power) metering rods, and .095 secondary jets, and typically a bigger engine. From Edelbrock’s chart (see above site, owner’s manual) we tried .083 main jets, .067x.055 rods, and .089 secondaries, and hoped for the best. I also put in the ‘off road’ kit, PN 1465, and a 1” phenolic spacer under it (heat was ‘boiling’ gas in the bowl). This got me through the trip, but with considerable difficulty keeping it running under higher power, higher elevations (seemed pretty rich). Gas mileage for 500 miles was not much over 8 mpg!
By then, I’d had enough of trying to get someone else to set up the carb right, and with this elevation range in my ‘back yard’ I decided I’d best get this beast figured out myself. I got with Larry at Edelbrock tech support (found them <very> helpful, by the way). I bought the calibration kit, PN 1486, and got a few more sizes of rods along the way.
Knowing I didn’t know much about tuning a 4bbl carb, I also sprung for an O2 (air/fuel) exhaust sensor, and a dash mount meter (http://www.summitracing.com, PN SUM-G2989 and Cyberdyne digital (LED)). This really made the difference! I could finally measure the mixture, not guess (even though metering is <too> sensitive, one has to do kind of a visual running average). It turned out I was running way lean at cruise <and> way rich at power, even before compounding this with the elevation change.
Since then, I’ve tried quite a number of metering rods and jets. I won’t bore you further with all the combinations (send me a note if you’re curious), but here’s what I’ve ended up with as the best I can find for my rig, YMMV:
.083 main jets, .065x.057 rods, .089 secondary jets. At 5000’ this combo sets me a bit lean on cruise (as I like), and a bit rich on power (I’d rather be nearer neutral, but they don’t make the ‘perfect’ rod, my guess is ideal would be about .065x.059, since I’m more likely to go up than down in elevation). Mileage now runs more like 12–13 mpg around town, and in one run up to 10,000’ and back I got nearly 16. Big improvement! Sounds and feels much happier, too.
I also will carry .068x.057 rods (likely about right for cruise at 9-10,000’) and .070x.057 rods (for higher elevation cruise). Unfortunately, there aren’t any rods available that lean out the power side in this range. I could go to a still smaller jet (.080 and .077 are available), but then I’d be way lean on the cruise side. If I get a chance sometime, I will experiment with the .080 jets and .065x.057 rods at higher elevations, though swapping out jets requires opening the carb body, not something I’m excited about doing on the trail. Note that changing the rods is a breeze, accessible right under the air cleaner.
Whew, way longer than I’d have liked, hope this helps someone!