Edelbrock 1400 Carb.

[tthornt]

I changed primary jets to .95 Now I have a light bog, during the transition from cruise to power mode. I emphasis is cruise mode, trying to get better gas mileage. My Question is - Should I go with a weaker metering rod spring and a 75/47 metering rod. or a stay with the orange spring and just change the metering rod.

Thanking your in advance again!!!!

[INSIDIOUS '86]

Is this under light throttle to full while moving? It may need slightly larger pump nozzles. Usually the cruise is tuned for mileage on most carbs by leaning tho mixture till the Infineon lean surges then jetted up two sizes on the holley.

On an edelbrock change the jet to get top end mixture then use the rods to tailor the the mixture at different throttle positions and the springs to give the right curve.

Idle mixture initial timing and engine idle rpm can make a big difference too.

Try a little stiffer spring both sides don't have to be the same. Good way to test the transition is going up a hill
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[Jabes1]

Best advice for tuning a carb, get a wideband O2 meter, such as one from Innovate. You can see exactly what your changes are doing... it is possible you are too rich in some areas and that will cause a bog as well. Its been awhile since I've messed with a carb since I made the switch to EFI, but Edelbrocks are pretty simple and the chart they have for jetting simplifies it. They make lots of tweaks for these carbs, shooters, jets, rods, springs and such. I had a blower under an Edelbrock carb, it would cruise at 16:1 afr and WOT was 12.5:1. I remember using the medium springs, the primary was a fat rod, don't remember the size and the jet wasn't huge either. Idle is super easy to set up with a vacuum gauge. Warm the truck up, close the screws, back them out 1/4 turn at a time to achieve the highest vacuum reading. You want to have both screws the same. Tuning a carb can be done without a WB, but its just a guess and takes more time to setup than if you had one. WB adds precision to jetting.

[Jabes1]

Look at the metering rod, its thinnest at the tip, fatter at the middle. The selection of springs dictates under vacuum how soon or late the fat part of the rod is used. High vacuum, such as idle or light cruise you will be using the fat part of the rod. Transition is the thin part if I remember correctly. If your engine is mostly stock, you shouldn't have to mess with the shooters or the pump shot. Gas mileage will be in the primary jetting and rod selection. Also, timing has a huge impact as well... if you have an HEI, make sure your vacuum advance is hooked up to the correct port which should be full vacuum.

[tthornt]

Yes, the bog (Is this under light throttle to full while moving)
Timing is set to 14 (advanced were plugged) i used Vacuum gauge to maximixe the vacuum. Electric choke is set two motches the right of the index mark.
currently - Metering Rods: .073 x .047. Step-Up Spring: orange (5" Hg).
95 jets in the primary and secondary.

I'm thinking about trying a bigger spring, and leaner rods 75/47.
What do your think?

Thanks for responding

[Jabes1]

Unplug your vacuum advance, I've never understood why people do that. I can understand doing it to see full advance and at what RPM its coming in at, but not on a street vehicle. Full on drag car wouldn't use vac advance, you could lock out the distributor, it never cruises. Hook up your Vacuum advance to full vacuum, you will get better drivability and mileage out of your truck. Here's an article you should read.... the whole article is good, but if you're not one to read, at least check out the timing and vacuum advance 101 section. http://www.chevytalk.org/fusionbb/sh...hp?tid/248441/

Secondly don't make too many changes at once, you wont be able to tell what change made a difference. Change the rod, then the spring since you tried changing the spring already. The stiffer spring is going to keep the skinnier part of the rod up longer, richening the mixture, while the softer spring will keep you leaner longer. Thirdly, double check that the throttle is cracking open all the way when the throttle is fully depressed and also that the choke is fully open when warm.

Like I've stated before, you'd be surprised at how lean you can run and how responsive a carb can be. Its possible to be too rich, seriously.

Try the 75/47 your leaning cruise with the bigger 75 portion while staying the same on the trans part. I remember running bigger jets in the back, smaller in the front with a fat rod... I wish I could remember what they were... it was like 6 or so years ago. I always used the medium spring, orange I think. The worse thing that will happen is it will backfire when you're too lean, so pull ove,r richen it by either changing rods and or jets. I used a bent paper clip to pick up the jets out of the fuel bowl. Don't run it too lean for a long time, that will cause damage, not a few incidents while tuning.

[tthornt]

Update: I've changed the springs to the silver, and the slight bog is gone. (I'm still experiencing: the truck is being held back during cruise) I'm going to change the rods to 75/47. Also, correction on the vacuum advance- I plugged the vacuum advance when I set the timing to 14. I never ran the truck with the vacuum advance plugged.
I'm going change the rods, test drive the truck, then contemplate reducing the timing to 12.

prechiate ur