Topic: Help me tune my Edelbrock carb.

[Dimitri13]

I've concluded that the carb on my Ranchero is too big. I've never tuned a 4bbl carb before, so I don't really know what I'm doing, but I have tuned my CB's carbs quite a bit.

Specs:
Ford 400M @ 130k mi
Weiand 8010 manifold
Edelbrock 1806 Thunder Series AVS 650cfm
Timing advanced to the verge of pinging
Everything else stock

Problem:
650cfm carb is too big. 500-550cfm carb recommended for a *healthy* engine of this size. Bottom end is extremely rich and will bog out with any spirited throttle input, fouls up the plugs when idling (stumbles with throttle for a few seconds after idling for more than 10 seconds), stumbles and bogs out at WOT unless I slowly accelerate (with the pedal) to WOT. WOT also sounds rich (exhaust note says so). Are there any adjustments I can make to make it flow like a 500-550cfm carb? A new carb is not in my budget until I finish my bike and get the Vette roadworthy.

Here are the carb's specs:
Primary .095"
Secondary .098"
Metering Rods - .068" x .047
Step-Up Springs - Orange (5" Hg)

Can I put the jets and rods from a 500cfm version of the Thunder series carb to get *about* the same performance? (.086" primary, .095" secondary, .065"x.052" rods)

[scottly]

Too large of a carburetor normally results in a lean situation, not rich. Your symptoms also point to a lean condition. Are the sparkplugs black and sooty? There is a jetting kit for the Edelbrock/Carter carb with an assortment of jets and needles.

[Dimitri13]

Really? I had no idea. Why is that?

Anyway, I did go outside and check the plugs after I posted this, and I checked half the plugs (two on each side in the front since they're the easiest to get to). Most of them were on the lean side.

I only thought it was rich because at idle it smells fairly rich, and after bogging the engine at WOT it smells rich in the cabin. But obviously the plugs say otherwise.

I cannot find a jet kit in stores here (checked the big 3 as well as the local speed shop), so I'd have to get it off Amazon or something. The O'Reilly with the speed shop has most of the jets, rods, and springs in stock though. It's roughly $55 for a jet kit and $25 for a set of rods and jets, so I get two tries to get it right by buying individually, so I'm not sure which is worth it. Plus the individuals are on island.

What should I be doing? An automotive carb is foreign to me, but I'm trying to understand it (I have one of those how to modify/rebuild edelbrock/carter carb manuals).

Is there anything I can do with the timing, maybe retard it a few degrees?

[Dimitri13]

Mmkay another part:

Runs okay when cold/warming up, starts running like crap (the details I pointed out before) when it's hot. Temp gauge seems accurate and doesn't really ever go above half (between the bottom where it starts registering temp and "warning").

I got it nice and hot now (was in school traffic) and will vacuum tune everything (timing and idle mixture, timing only because the harmonic balancer damper slipped and it no longer lines up, a common problem) and report back. I'm looking on craigslist for a used 500cfm-ish carb, as well as listing some corvette parts, so maybe I can afford a new one.

[Edit] The bogging out at WOT and anything more than moderate throttle is more like stumbling, and sometimes shudders (like you would shudder off the line in a m/t with poor clutch control).

[Bailgang]

Considering almost every Quadrajet carb out there is at least 720 cfm with a few up to 800 then 650 cfm on your engine shouldn't be a problem in fact I used to run a Holley 780 on a 4 barrel Cleveland and it screamed. What you need to understand is that all of the off the shelf aftermarket carbs very seldom work perfectly right out of the box and need to be tuned for the application you're using it for. I think your Edelbrock carb is an updated copy of a Cater AFB and Edelbrock should have a tuning kit available for it. It's been a long time since I priced the kit but the two I purchased for the Edelbrock carbs on a 455 Pontiac I had gave me a selection of different metering rods, jets and so on to dial my carbs in. I needed two kits because I was using a low rise dual 4 barrel intake.

[Dimitri13]

I understand the jetting or rods may be off, but I don't know which was to go or how much.

I just adjusted the timing slightly (retarded it 1 or 2 degree) and richened up the idle mixture, got me to roughly 19 in/hg, which is about the limit of pinging.

[scottly]

timing only because the harmonic balancer damper slipped and it no longer lines up, a common problem) and report back.

If you know the balancer has slipped, it needs to be replaced. In extreme cases the ring can fly off.
The 383-440 Mopars were fitted with Carter carbs stock, but I don't know the CFM rating. I replaced the stock Carter on a 413 cubic inch motor with a Holley 780 due to issues similar to yours. It seemed to be fixed at first, but the symptoms returned. The real issue turned out to be bad resistor spark-plug wires..

[Dimitri13]

Hm. I completely forgot about the ignition system. I should probably replace the rotor, cap, and wires. Maybe the plugs, they're newish, but obviously tortured by the carb.

Or at least I think the balancer slipped. Setting it to stock timing (8° BTDC) and even advanced (16° BTDC), it performed horribly. Right now it's at probably 30°+, but I don't know the exact number because the marks on the balancer don't go that high.

[scottly]

You need to do some trouble-shooting before you start spending money. Did you disconnect the vacuum advance before checking the timing? What year Ranchero?

[Dimitri13]

Yes I disconnected the advance when I timed it.

It's a 78, based on the Thunderbird.

[Don R]

A 625 isn't really large on a 400 cid engine. I have one on my small block chevy 350 and  it works well.
 The acceleration bog sounds like the accelerator pump isn't working, the pinging may be due to timing issues. You need to check the centrifugal and vacuum advance units and either replace the dampener or at least find TDC on #1 and put a proper timing tape on it so you know what the timing really is. I'm auctually considering a holley 780 double pumper on my 350. Now that's a lot of carb. My 567" big block has a 1250cfm just for perspective, lol.

[Don R]

The AVS is an air valve secondary. The secondary will only open if the engine vacuum sucks it open, so it operates on the front two barrels until you put your foot in it. Really an effecient design a should be an excellent carb for your Ranchero.
 It's been around for decades, mine is a Carter version I think 9625.
Fuel pump pressure shuld be checked also, I believe the float level is checked pretty much like a sohc honda, the top lifts off and the floats hang from the top, I'm thinking you turn it over and measure the float heigth. No spring loaded pin in the needle here.

[dusterdude]

Its not too big

[Retro Rocket]

Its not too big

+1, I had a 650 double pumper Holley on a 4.2 liter V8 {253CI} and it flew, a tad rich down low but it ran beautifully, engine was worked a little bit...

[Dimitri13]

Well, this engine stock had 156 hp. After 130000 mi and 30 years, I would be surprised if it had more than 100 hp now. The stock carb was a Motorcraft 2150, a 2bbl 351cfm.

[Bailgang]

Well, this engine stock had 156 hp. After 130000 mi and 30 years, I would be surprised if it had more than 100 hp now. The stock carb was a Motorcraft 2150, a 2bbl 351cfm.

When I was a mechanic in the early 80's I worked on a bunch of 351 and 400 "M" engines and hated them but never had problems with genuine Clevelands. We called the "modifieds" but I don't know what was modified about them other than the fact they had a load of power sapping pollution control devices on them compared to a genuine Cleveland.

[seanbarney41]

yup, that's where all your "v8 power" went...what have you done with the EGR system, also make extra sure you have no vacuum leaks

[madScientist]

Well, this engine stock had 156 hp. After 130000 mi and 30 years, I would be surprised if it had more than 100 hp now. The stock carb was a Motorcraft 2150, a 2bbl 351cfm.

156 hp base? Granted I dont know much about the late 70's engines before I built up an engine for the 66 Mustang I had a stock 71 302 that was putting 200 to the rear wheel but it was still pretty healthy. I have a 1804 on a 347 that seems to be running pretty good but I'm with you in learning how to tune Edelbrocks. I've always been a Holley guy.

I'll root around some of my books...i think I have an Edelbrock tuning manual floating around somewhere.

[Dimitri13]

Not sure why people call it "Modified." The "M" stands for Michigan.

As far as I can tell, most of the emissions stuff is not there. There's no A.I.R. pump, no EGR, etc. As far as I can tell, there's no vacuum leaks. Most of the vacuum hoses are relatively new and everything was done properly.

[Dimitri13]

Turns out the transmission  kickdown thingy came off the pivot. All is well for the most part. Now it's just a matter of getting the timing right.

Is it possible to stab the rotor in (pulling the rotor up and turning it) while the dizzy body is still fully locked down? I think I may have done that if it's possible.

[madScientist]

i dont think that's possible. I believe the diz has a c-clip that holds the rotor shaft to the gear. It's not terribly difficult to pull out and rotate a little. Although a word of advice...have a long magnet ready for if the shaft that goes into the oil pump comes off. A little rtv silicone on that will help when putting it back in.

[scottly]

I stabbed a 390 distributor in today, and it absolutely has to have the locking bolt removed to clock the rotor. The interesting thing I found was that the motor wouldn't even try to start unless the initial timing was set at 20* or more, no doubt due to a slipped balancer ring...

[Dimitri13]

Okay that's what I was thinking. I finally replaced my cap rotor and wires. Took a look at the rotor, and it can only go in one way.

Lots of trouble with this procedure though. First I replaced the cap, one wire at a time, to ensure I didn't mix up any wires. Finally found at the end that I mixed up 1 and 8. The center tang of the rotor got bent somehow and was like making the cap move around all wierd. Oh and the plug wires I bought were not premade, only the plug boot was on. You had to cut, crimp the connector, then put the dizzy boot on. First time I've ever done that. Plus it was suppression core wire, so I wasn't entirely sure how to do it at first, so I ended up with the coil wire being 1/2" or so too short so it's taught.

And at some point during this I was getting a misfire and I thought maybe the timing would need to be different because I was getting more spark or something, so I messed up my perfect timing (hard to set because slipped balancer ring and have to do it by ear or vacuum). That misfire was from the switched 1 and 8 wires.

[Dimitri13]

Turns out my fuel pump is going. Whodathunk?

[madScientist]

I was going to suggest checking fuel pressure. The Eddy's are real sensitive to fluctuations.

[Dimitri13]

Turns out it wasn't just the fuel pump. I'm thinking it's a clogged in-tank filter.