http://forum.studebakerdriversclub.com/showthread.php?52219-60-lark-ragtop-carburetor-amp-mpg-problem-final-update-w-pix If it's a 1406 600 CFM carb you have .098 jets in the front and 75/47 rods as standard equipment. Use your manual to find the smallest jet and rod combination you have in your recalibration kit. If you are careful when you remove the top you won't need to replace the gasket. Do the job with the carb off the car so there's no chance of anything getting in the engine. The jets just unscrew and the rods pop out when the covers are moved to the side. When you re-assemble it's easiest to install the rods after the top is bolted on this way there's no chance of ending them. MY suggestions are based on the assumption that your engine is basically stock or mildly upgraded. On your test drive look for flat spots on mild acceleration as in going up a slight incline where a little extra throttle is applied. If you feel a flat spot change the spring for the rods to the strongest, I'm forgetting what color that is but it would correspond to the highest vacuum rating. If the car still has flat spots or is not pulling to the redline without flattening out look for the next richer rod which is a lower number than the smaller number on the rod. If its lower on both sides that's ok as long as it is paired with your jet size in the manual, 73/45 for example. The numbers may be different than what I'm typing here as these are just examples. If you can picture what's going on the process will be easier. At idle and high vacuum that rod is pulled down inside the jet. so using your stock configuration you have a .098 jet minus a .075 rod so the hole the fuel is going through is .023. As you accelerate vacuum drops the rod is pushed upward by the spring and that hole becomes .098 - .047 or .041. The different jet and rod combo's change the size of that hole for best economy and cleanest acceleration. The springs are different because some HP cams make less vacuum so they need to be weaker to allow engine vacuum to pull that rod into the jet. You can increase throttle response by changing springs to stronger ones if your cam is not hurting vacuum. The stronger spring moves that rod up faster so you get a little more fuel on light accleleration as vacuum drops eliminating flat spots. The process is trial and error and you may have to try different combinations but from experiece I know that the stock Edelbrock 600 jetting is even a little large for an un-modified Chevy 350. ErnieR ------------------------------------------------------------------------------------------------------------------------------------------------------ Just figure out what the jet/metering rod/spring combo are for your carb find that setup on the on the graph style chart with the shaded area and lean it out 1 unit. If it's really rich 2 units. That assumes the the fuel pressure and advance are correct but they are really straight forward to adjust. I dropped mine 2 units with jet/rod changes and then used the springs to adjust even further. Sweetolbob ------------------------------------------------------------------------------------------------------------------------------------------------------- Been driving my 259 Daytona for a few days with the new setup - went 2 stages leaner with the strongest spring (silver, 8" vaccuum). Main jet is .083 and metering rod is #1460 (065 x 052). The metering rod is what comes stock on the carb. Driveability is very good, no flat spots or bogging. A/F numbers are at idle in neutral (around 800 rpm): 14.0 - 14.3 at idle in D (about 600RPM): 14.4 - 14.7 cruising at 65 (about 3000RPM): 13.8 - 14.2 steady acceleration: 13.5 - 14.0 WOT: 11.5 - 12.0 This looks like a decent range, keeps it on the rich side during acceleration where a lean condition could lead to burned valves. I'll run it a few more days and pull the plugs to see what they look like. Pdrnec, sdc forum - 0611 ========================================================================================================== http://forum.studebakerdriversclub.com/showthread.php?52137-Jetting-an-Edelbrock-1403 Jetting an Edelbrock 1403 Been using Edelbrock 4bbl carbs for a while, always seemed to work well but ran rich. When I put the last car together (63 Daytona 259) I had a bung welded in the exhaust for an O2 sensor so I could plug in the Innovate LM-1 air/fuel analyzer and solve the problem once and for all. Not surprisingly, the stock 500CFM carb is jetted too rich. I stepped the main down from .086 to .083 and still was running rich at cruise. Dropping down to .080 gives a very slightly rich condition - around 14.0 - 14.5, very acceptable as the ideal is 14.6 according to Edelbrock. Going a little richer gives better performance, a little leaner better economy. Acceleration was still rich, I wound up with a 1463 (067 x 055) metering rod and a lighter step-up spring (yellow, set for 4" vacuum. stock is orange, 5" vacuum) I'll drive it for a while and see how I like it and what the plugs look like after a few hundred miles, but it seems to get off the line much better. Might play with a 1406 later and see if there is any difference. Pdrnec ------------------------------------------------------------------------------------------------------------------------------------------------------- Dont forget to mess with the springs in the metering rod pistons.. They'll have a lot to do with the cruise fuel. They'll change the position of the rod inside the jet. "Just" changing the jet is only 1/3'd of the adjustment available on the "primary jet" end of things. So you have to adjust - 1. the jet 2. the metering rod 3 the vacuum piston spring These all seperatly and together, have a great effect on the primary side fuel metering. Mike Van Veighton -------------------------------------------------------------------------------------------------------------------------------------------------------- Thanks Mike - that's the spring I mentioned. The biggest discovery was how small a main jet was needed. The adjustment Edelbrock sells only goes down to .083, I had to order the smaller one. pdrnec -------------------------------------------------------------------------------------------------------------------------------------------------------- OK, pulled the old cast iron manifold and installed an aftermarket aluminum intake with the carb heat passage blocked. Paid close attention to eliminating possible vacuum leaks, put a different 1403 on it as one of the rods was sticking on the other one. Used the stock spring and rod ( orange 5" vacuum spring, 1460 (065 x 052) rod) with a .083 main jet. It's right at 14.6 at idle, low 13s on acceleration and low 14s at cruise. I'll run it this way for a few days and play with timing to see if I can improve low RPM performance as it's still a bit pokey off the line. pdrnec