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Old 06-30-2012, 06:44 PM
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Edelbrock 1406 question wot lean

Hope I can get some insight from someone out there, I have a pretty stock SBC I've gotten the jetting I think pretty well under control now but I need some clarification as to if I'm on the right course. Using their tuning chart and a narrow band A/F gauge(sorry) but it did seem to help. I was running really lean throughout the full range. I decided to start with position 17 ran pretty well but poor acceleration. moved to position 18 acceleration much better and very drivable. Only thing is when you stand on it it goes real lean, here's where I need some info. The primary's are what you are using just cruising around town, and the secondaries come into play only when you stomp on it? or do the secondaries modulate in as needed brought on by vacuum? I'm thinking on changing the secondary jets to 101's from the 98's that I had put in. As I said it runs really well using the tuning chart at #18 just it sort of drops off when you stand on it and the A/F gauge just goes way lean. If someone could help me with the secondary circuit that would be great. Thanks, Eric
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Old 06-30-2012, 07:33 PM
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The metering rods and springs are what control the A/F at part throttle power mode. Secondaries will assist in controlling the WOT, along with the primaries. So, if you have the cruise and mid-power set right and you still more at WOT you'll need to increase the secondary jetting.
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Old 06-30-2012, 07:53 PM
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Thanks that was what I was thinking as well, the Edelbrock instructions don't really go over the Wide Open issue as well as the other parts, the rest of the jetting they seem to go over pretty well. I appreciate your response I was just wanting to see if I was on the right course. The engine runs great except for when you tromp on it. Thanks again
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Old 06-30-2012, 08:06 PM
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Is it going lean as you transition from light throttle to strong acceleration, or is it going lean only when you go to WOT?

If the meter goes lean during fairly aggressive part-throttle acceleration you can sometimes improve it by swapping step-up springs. Going to a higher vacuum spring will make the transition from cruise to power on the primary rods happen a little sooner, and this can help a lot to resolve a part-throttle bog.

Once you reach WOT you have kicked in the secondaries, and your jet changes should help if that it where it shows lean.

Bruce
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Old 06-30-2012, 09:16 PM
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WOT at what engine speed? What did you change your rods and jets to? I don't know their "steps" I just know rods jets and springs. You may need to go to a thinner second step on your rods. Your secondaries only come in at high engine speed and WOT, not low engine speed and WOT.
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Old 06-30-2012, 10:41 PM
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I didn't even think to mention engine speed, I don't have a tach but it's a turbo 350 trans and going 40-45 mph and then floor it, just watching the A/F gauge it never moves off the total lean position until you back off the gas. If you don't floor it and just fairly hard acceleration it pulls real strong and the a/f gauge is steady and not pulling into the lean area.
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Old 07-01-2012, 06:12 AM
How fast is fast enough?
 
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If your truck downshifts when you floor it then its the secondary jets, if it doesn't then its the second step on the primary rod.
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Old 07-01-2012, 07:39 AM
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Based on your latest post, is very likely that you can fix the problem with only step-up springs and primary rods. These are very easy to swap.

All the primary rods have two steps, for cruise and power, and they are marked with numbers like 7547. The larger number is the cruise step and the smaller is power. A smaller number means a richer mixture, since the rod sticks down into the jet and reduces its flow. You could try something like a 7542 or 7537, which would keep cruise the same and richen the power mode.

Vacuum pulls the rods down into the jets so that the thick (75) part of the rod is in the jet (cruise). When you accelerate hard the vacuum drops and the springs push the rod up so that the thin (47) part of the rod is in the jet. The rating of the spring determines how low the vacuum has to go before it transitions from cruise to power. A higher rated spring (e.g., 8") will transition to power sooner than the stock 5" spring in the 1406 when you accelerate.

You may also need to adjust the accelerator pump shot, but I would try that last. Many folks try to fix the Edelbrock bog with the accelerator pump, while the real fix is (1st) get the right step-up spring, and (2nd) pick the right primary rod combination.

Bruce
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Old 07-01-2012, 08:23 AM
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Thanks for the thoughts, I think I might have 75/42's here to try, since it's Sunday my choices on availability aren't the best. I appreciate all of you working with me on this I thought I was on the right track and it seems I was, it helps to have it explained in non Edelbrock terms sometimes. I'll check what I have and give it a try. Thanks again. Eric
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Old 07-01-2012, 03:19 PM
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Any all exhaust leaks (fore and aft of the O2 sensor) and or having the o2 sensor too close to the end of the exhaust pipe will cause the AFR gauge to read false lean @WOT

high rpm WOT leanout ='s lack of fuel system flow volume.
For a high performance application using the 600cfm eddy carb start with this calibration

.098" pri jet .068x.047 pri rod .101" sec jet. 4" to 6" piston strep spring.

5psi fuel press at idle. not less than 3psi @WOT high rpm.

Your narrow band O2 should stay pegged at .800 to .850 V @WOT.
you got a leak in the exhaust system. or the ignition system is misfireing or both.
or your fuel pump, fuel lines, in tank pick up tube or fuel filter is fubared

Last edited by F-BIRD'88; 07-01-2012 at 03:34 PM.
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Old 07-01-2012, 04:55 PM
How fast is fast enough?
 
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Quote:
Originally Posted by F-BIRD'88 View Post
Any all exhaust leaks (fore and aft of the O2 sensor) and or having the o2 sensor too close to the end of the exhaust pipe will cause the AFR gauge to read false lean @WOT

high rpm WOT leanout ='s lack of fuel system flow volume.
For a high performance application using the 600cfm eddy carb start with this calibration

.098" pri jet .068x.047 pri rod .101" sec jet. 4" to 6" piston strep spring.

5psi fuel press at idle. not less than 3psi @WOT high rpm.

Your narrow band O2 should stay pegged at .800 to .850 V @WOT.
you got a leak in the exhaust system. or the ignition system is misfireing or both.
or your fuel pump, fuel lines, in tank pick up tube or fuel filter is fubared
That first step on your rod seems a little rich for decent mileage. Id go 70 or 72 but to each their own.
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Old 07-06-2012, 03:00 PM
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Ran home at lunch and installed the 75/42 rods and did a couple of laps around the neighborhood, seems better using the same route going up an incline and then trying stomping on it,didn't get the ping during stomping on it and much smoother during heavy acceleration,going to recheck the timing and the idle mixture screws but pretty happy with it. Thank you all.
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Old 07-06-2012, 03:39 PM
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aren't the 1406 the one calibrated for fuel economy ?

you can just check the specs on the 1405 carb and swap those jet sizes into yours
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