question about mpg with 1406 edelbrock

[ol yellow 72]

heres what i have bone stock 77 chevy 4x4 350/350/np205 no front shaft, 31x10.50 3.08 gears, 2 inch dual exhaust

i installed a new 1406 edelbrock and im now gettin 6 mpg, i adjusted floats, and have done everything i know to do

so my question is is this normal or do i need to trying to jet it down or what

ideas please

[tucsonjwt]

Just a thought, I had a small leak at the fuel inlet nut but did not notice it since the fuel evaporated when it hit the intake manifold. When the leak got worse I could smell gas inside the cab - then I could see it visibly leaking on the intake. Maybe you can pop the hood with the engine running and work the throttle to see if you can detect a leak.
31s won't help gas mileage, and a 4 x 4 cuts mpg, but were you getting better mileage before the new carb? The best I ever got with a C20 350/350 2WD was 9 mpg city.

[GMC Guy]

with my 1406, i get 13-14 mpg highway. i don't even keep track of the in-town lol
350 with bolt-ons, th350, 3.08s
and that's keeping it 75 and under on the highway, turning 2700-2800 rpm

[swb85]

Make sure your choke is working properly. You also may need a rod/jet change, the factory calibration might not be what your combination wants.

[78 Chevyrado]

You need to adjust the rods and jets to "dial it in" I have a 1406 on my bone stock 350 in my 78 3/4 ton and nothing except the float level is set the way it came out of the box.

Also if you don't have a regulator on the stock fuel pump, you will need one and set it to 5psi or 5.5psi. Stock fuel pumps in my experience put out 6-9psi, which is way too much and can unseat the needle valves in the bowls.

I have the Edelbrock 1487 Calibration kit. I've had to use it on every carb I've had.

In the 1406 Manual, My carb is set to the black circled 8 on the calibration reference chart which is about 6% lean on the cruise Mode and stock on the power mode. And I've changed my secondary jets from the stock .095 to .101 And I'm using the Orange springs. It's a night and day difference. You're gonna waste some gas, but you just change a setting one at a time and go try it out.

[ol yellow 72]

i removes the top of the carb again today and it appears the jetas may have been changed, althought my friend who i got it from swares it hasnt it has .98 primary and .98 secondarys is this right??

also i was gettin 15 mpg with my quadrajet before i put the edelbrock on
and the choke assembly has been removed because when he bought it he has it on his mud race truck and did aaway with the choke

[78 Chevyrado]

Mine came with .095 jets all the way around when new, but this was in 2005. edelbrock could have changed what comes stock since then.

Don't know where to find another choke, but you'll want to have one for winter driving. how do you get it started now?

I get around 15-16MPG out of mine, and it's a 3/4 ton. Just tinker with it until it doesn't improve any more. And remember where your settings were before you tinker and you can't go wrong, you can just stick it back like it was.

EDIT: Mine DID come with .098 Main Jets, but had .095 Secondaries. Thanks Cue-Ball.

[swb85]

I'm betting that carb is set up richer than donald trump.....it would almost have to be to start without a choke in this cold weather. Get yourself the calibration kit listed above and start leaning that puppy out.

[Cue-Ball]

From the factory the 1406 uses 75x47 needles and .98 primary jets. I can't remember the stock secondary size. It's either .98 or .95, IIRC.

I run a 1406 in both of my vehicles. The one on my truck ('80, 2WD, 305, 2.73 gears) had to be enrichened under power. The stock cruise settings were pretty much right on, straight out of the box. If your mileage is as bad as you say it is, I'm betting it doesn't simply need rejetted (though, you probably will need to make at least minor changes). I'd guess that something else is very wrong. My truck only got 8 mpg when I bought it. Pulled apart the carb and the driver's side needle was bent, not even going into the jet. Fixing that was an immediate performance and driveability improvement and an increase of 2 mpg.

Even after getting the carb dialed in, my mileage is not great at about ~11 mpg around town. You're hauling around a heavier truck with more drag (4WD, bigger tires) and deeper gears. I'm sure you can get more out of it than you are now, but don't expect too much.

For what it's worth, right now I'm running .098 main jets, .092 secondary jets and 73x42 rods. A pair of 75x37 rods arrived last night and will be installed this weekend, along with some .089 secondary jets. That should be pretty near perfect I think, but we'll see what the wideband says.

Make sure everything else is good before you get too heavy into jetting changes and such. You want your timing curve to be correct, getting good spark, etc. before you go wild with carb changes.

[454HO]

Which port did you hook up the distributor vacuum advance to? My guess is you hooked it to ported like the Edelbrock instructions say. If so, then you probably had to open up the throttle with the idle adjust screw to get it to run. When the throttle is opened up to compensate for retarded timing at idle, then too much of the transfer slots will be exposed and it will be running pig rich. A quick check to see if this is the problem would be to pull the carb off the intake and flip it over to see the transfer slots. They should be 'squared' which means they will only be opened to about .040" or so. Any more than that will waste gas.

If this is the problem, the fix is just to turn the idle adjust screw to square up the T ports. Reinstall the carb, and DO NOT TURN THE IDLE SCREW AGAIN. Instead, adjust the initial timing to to whatever it takes to get the idle around 650rpm or so. Then hook up the distributor vacuum advance to the full manifold vacuum. It should increase idle speed a bit more.

Attached photo is of a 1407 carb with way over exposed transfer slots. I had this carb on a mild 454 and it idled great, but it was waaay too rich. It also had a slight stumble on light acceleration. Squaring the slots and increasing timing as suggested cured those problems.

[evan]

Originally Posted by Cue-Ball

... but we'll see what the wideband says.

Can you give some more details on what type of sensors you use and how you use them?

[Cue-Ball]

Originally Posted by evan

Can you give some more details on what type of sensors you use and how you use them?

I use an Innovate Motorsports LM-2. It's pretty simple, really. I drilled the exhaust and welded on an O2 bung where the left and right sides Y together (I've got a 2-into-1 stock style exhaust, but you could just as easily tap into an X-pipe, H-pipe, just do one side, or do both sides). Thread the O2 sensor into the bung, plug it into the LM-2, and plug the LM-2 into the lighter socket. It gives a readout of the A/F ratio at that particular moment and has a display that let's you see the last 30 seconds or so as well. You can also record the A/F ratio to an SD card and look at it on a PC, but I don't bother with that. I just turn it on and watch it while I drive, just like watching my speedo.

Using this tool I can see *exactly* how rich/lean my truck is running, rather than just guessing. I found it online for about $250 and it was worth every penny. I own two carbureted vehicles (soon to be three) and it takes the guesswork out of tuning them. Sure, it still takes trial and error of different jet and rod sizes, but I know exactly how rich or lean it's running without making timed passes, trying to read plugs (which doesn't work), or any other voodoo. Just take a quick drive around the neighborhood, see how the sensor reads, pull in the garage and make the necessary changes.

If you REALLY want to get in depth, there are options to hook up multiple O2 sensors, a throttle position sensor, vacuum/boost sensor, etc. I might end up doing that on my Camaro in the future, but for now the basic O2 ratio is good enough.

[BBCurt]

you may be close to what your truck needs, but the factory will never get it exact. get it tuned, and enjoy more power and economy