Fuel System: Jetting an Edelbrock 1403

[pdrnec]

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.

[r1lark]

Excellent info Pat - thanks for posting!

[Mike Van Veghten]

Pat -

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

[pdrnec]

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.

[Mike Van Veghten]

Interesting.
My 259 has one step smaller main jet, don't recall which rod and the middle set of springs (been years since I tuned the thing..!). It's actually a tad on the lean side. I have the idle mixture scews out a little too far, that's just enough to help the overall mixture.

Mike

[pdrnec]

Running a mild cam (sort of an ST-2 if there were such a thing) and 2 1'2" duals on a fresh rebuild. I'll keep an eye on it to see what it does.

[gohdes]

thanks for the good info.
I am having trouble with my 1403 as well. Have the calibration kit, but only goes to .083 jet as you mentioned.
I am getting very poor mileage, and it seems to really suck the gas!
Funny, my car came from Los Feliz last year!

[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.