GuitarJunki17

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Well guys, moving along here, making major progress with this tuning.

Everything up until WOT is beautiful, the car is running as healthy as I would have ever expected it. But whenever I mash the pedal to the floor, the car is acting as if it has 70hp. I adjusted the pump shot, and the response is there, but I mean from 0-60mph, it's taking about 10 seconds to get there. The throttle cable is giving full travel, and shift points seem accurate. It's like it just doesn't have the power. There's no popping or sputtering, it sounds healthy, just completely doggin' it.

Now, I read that this could be an extremely lean condition, and Edelbrock's tuning videos say the same thing, but my AF gauge is reading about two steps rich. (On a 10 step scale, with 5 and 6 being the 'green zone' it is reading an 8). And my plugs are black with soot, which leads me to believe that a lean condition is not the case here.

So, if a carb is running extremely rich, could I be getting the same symptoms? I've had the same spark plugs in since I have started this project, and the car has been run for maybe a total of an hour's time, maybe slightly more, and they are showing totally black. Could they be fouled and need replacement already?


I'm sooo close guys, help me out!

SETUP

Edelbrock 750 w/ vacuum secondaries and elec choke
Edelbrock performer rpm intake
15" hg vacuum
Pro Comp HEI distributor
10* advanced
6.5psi fuel (rock steady)
Comp XE270hr cam .495/.502 lift

sofakingdom

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That's WRONG.

Something is not as it should be there. You should be getting idle vacuum something like 15-16" of Hg.

Just for the fun of it, screw the timing light. Advance the timing until the idle vacuum is 15", and test-drive it, and see if it's any better.

I'm betting you have a stock balancer and a "chrome" or other cheap replacement timing cover; which will cause your timing mark to indicate about 30-35° more advanced than it really is. I.e., you THINK you set it at 10° advanced, but it's ACTUALLY 25° retarded.

GuitarJunki17

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Why would the step up springs only go to 9" then? Unless since there are two of them, you would add them together (giving 18" total?)

The balancer and timing tab are stock. I have used the combo to tune the TPI when I had that on there, and never had an issue.

Although I DO wanna check the vacuum again, because it was the first thing I checked before I got the idle RPM evened out so it wouldnt stall, so I held the pedal slightly to keep the car running (1000rpm TOPS), then got the reading.

Apeiron

The step-up springs control the point at which the carb enriches the mixture for more "spirited" acceleration.

If your AF gauge isn't a wideband type, and just uses a stock-type O2 sensor, you can pretty much ignore anything it has to say.

sofakingdom

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Don't argue. That won't make your car run better. Just try it.

GuitarJunki17

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Ha, alright, we'll see what happens. But I still dont understand that if my vacuum should be in the double didgets, why Edelbrock's step up springs stop at 9"

sofakingdom

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It's because they don't "step up" anything.

What they do, is as long as the vacuum is ABOVE whatever that value is, the carb stays in "lean" (cruise & idle) mixture mode; then when the vacuum goes BELOW that point, the spring tension overcomes the force that vacuum puts on the piston, and the carb goes into "rich" (power) mixture.

Basically, the exact same discipline as a Holley power valve, or a Q-Jet power piston spring.

GuitarJunki17

iTrader: (1)

So if you were to put a 9" spring in, then when the vacuum decreases to 9" at WOT, it will richen the mixture up?

On a rough scale, 9" springs would be for most power, and 3" springs for least power correct?


Another thing:

If I were to try the digital volt meter with my O2 sensor, would that be any more accurate than the cheap gauge I have?

Apeiron

Right.

No, the spring only changes the point at which enrichment happens, it doesn't change the amount of enrichment. A 3" spring will have you putting your foot right to the floor before you get any enrichment. Maybe good for fuel economy, maybe not so good for part throttle acceleration, depending on your driving habits.

Not really, the problem is the nature of the sensor itself. It's designed to tell the ECM only if the mixture is rich or lean while cruising for emissions purposes, but not by how much.

sofakingdom

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Also, the spring's operating point MUST BE lower than any vacuum encountered during "non-power" operation; i.e. idle & cruise.

Meaning, if you're measuring 7" of idle vacuum right now and have a 9" spring in there, your carb is enriching at idle; which of course will produce the sooty black plugs and the eye-stinging rich condition we all know and love. Your O2 reading is telling you the same thing.

Vacuum at WOT = 0"

That means, there's no difference in pressure between outside the intake manifold, and inside it. Which is of course exactly what you'd expect: you've got these ENORMOUS vacuum leaks called "throttles" that are busy connecting the intake to the atmosphere with four 1¼" holes.

Low-numbered springs (or power valves or whatever a specific carb uses) are necessary when running a big cam that gives low idle vacuum. But you don't have that, all you've got is a XR270HR, a nearly stock-computer-compatible street cam. You merely need to set your timing right so that your motor runs like it's supposed to, and go from there.

But for what you've got, a 9" spring should be fine, once you get the timing set right. Start there, and once it's right, serious tuning can begin.

GuitarJunki17

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Ha try telling that to my TPI system! But I actually believe the reason that the cam was hated by the computer was because of the 110 lsa.

I'm only joking though, you guys are really helping me out, uncovering things I have not yet learned about carburetors. I'll try to see if I can't get that vacuum back up this weekend. I don't see why it would be so low like that though (I hooked the gauge up to the manifold vacuum port on the carb...was I right in doing this?) But I'll look for leaks and stuff this weekend.

Are there any other problem areas for vacuum loss? As far as lines go,

-theres the one from the carb to the dizzy
-PCV to front of carb
-Brake booster to back of carb

Any more that I'm missing, or just not thinking of?

And then of course vacuum escaping from intake gaskets/carb gaskets, I'll check for that too.



Oh and just for the record, I do not have the 9" springs in right now, I was just using them as an easy reference. I have 7" in there now, but may go back to the 5" in light of new knowledge.



One last thing, can someone give me a product number for a suitable O2 sensor for tuning?

sofakingdom

iTrader: (1)

I don't think vacuum leaks are the problem. You don't have a problem with the vacuum "escaping", as such; the problem is that the motor isn't GENERATING enough.

Think of the engine as a pump. It's sitting there doing its damnedest to take the air out of the intake and put it into the exhaust. Meanwhile, you've got this little "leak" letting air back in, to replace what the engine has managed to move out; it's called the "throttle". The more effective of a pump it is at any given moment, the higher the manifold vacuum will be. The reason for your low vacuum is an engine that doesn't produce as much power as it should, and therefore isn't spinning as fast as it should be for the amount of air & fuel it's taking in, and therefore isn't pumping as hard as it ought to, because the spark is occurring at the wrong time (too late).

Yes, a manifold vacuum port on the carb is OK to use for testing; or, if there's one that goes into the intake directly, that's also OK. The main thing you need, is to be sure that it's not "ported" vacuum. That goes to the vacuum advance (usually).

There should be at least one other vacuum line, to feed vacuum to the HVAC controls (the various little doors that direct the air); maybe one to the cruise; maybe one to your charcoal canister if it's still there.

GuitarJunki17

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I'll check up on the charcoal canister, as I have not looked at it yet.

As of right now, I had the manifold port on the carb connected to the distributor. Could it be that I should have just connected the distributor to the ported vacuum port to begin with (the one on the left?)

Apeiron

You should have a lot more idle vacuum than that regardless of where your vacuum advance is connected. My XR282 still gets around 12 inHg at idle.

GuitarJunki17

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Oh, one more thing to throw into the mix that I forgot to mention earlier:

You guys are saying that the AF ratio meter will be inaccurate, but it started off with 9 bars filled when I started the car, and as the choke opened as the car warmed up, the bars slowly dropped to 7-8 (closer to stoich). How is this so if the narrowband system doesn't account for small changes?

Apeiron

All the gauge is telling you then is that the mixture went from "richer than stoich" to "still richer than stoich but not as much". You still don't know what the mixture was.

rjt76

fix your timing. fix your vacuum leak. put a holley 700 double pumper on their and enjoy your ride.

sofakingdom

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GuitarJunki17

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rofl, not arguing, just throwing in more factors.

Thanks guys, i'll have at it this weekend, but for now, i'll shutup

GuitarJunki17

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UPDATE: :note to self, don't let girlfriend be the one to read you your vacuum measurement:

Turns out I've had 15" of vacuum all along, it's a dual sided gauge and she was reading the wrong side, which read 7psi, while the other side read 15"hg.

So, with that I am ready to start changing out jets and rods. I've got the calibration kit for my carb.

Now, Edelbrock's site calls for a lean condition for my symptoms, and I said the plugs were black (rich), which COULD be from when I had the TPI system in. I'm putting a new set and ditching these ones, as they could be contributing to my problem.

So, to recap, idle = good, cruise = good, WOT = sloooow. Would you think to richen up the mains and secondaries, or would they need to be leaned out? Just mains, just secondaries?

Cmon carb tuners, need your help.

contact

what is the manifold vacuum reading?,
when you think it is way underpowered
at WOT.

are you sure the air valve is opening?

sofakingdom

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You can only read plugs when the ONLY THING THEY'VE DONE is the condition you're tuning for. I.e., if you're trying to tune WOT, you put a new set in, do a WOT blast, SHUT THE ENGINE DOWN WITHOUT LETTING IT IDLE, and then read the plugs. If you're not doing that, then the soot you're seeing on those plugs probably didn't come from WOT.

It is entirely possible for a carb (or FI for that matter) to be setup to idle too rich and be too lean at WOT.

How does it run with the timing set just below the point at which it begins to ping?

GuitarJunki17

iTrader: (1)

Well, at first I decided to take it safe and go a tad leaner with the tuning. Did that and it ran like hell. I even got a nice fireball through the carb too, damn near took my nose off

But, I got on the phone with Edelbrock, and asked the tech what his opinion is on whether to tune rich or lean. He was positive that it had to go richer with the cam I had. He reiterated that the carb is tuned lean from the factory and there's no way that one stage down towards lean, or even stock for that matter would work properly. He recommended me a combo and I tried it out (one stage rich on power, and one stage rich on cruise) and it felt better. Still lacking power at WOT, but smooth, and a little more powerful than before. I ran out of time today because I had to come back to school, but next weekend I'm gonna go richer and see what happens.

Oh yeah, plugs are still clean too, so that pretty much solidifies it. I can see down the shaft of it, and it's clean all the way down (bottom of the shaft would be a reading at WOT, middle would be cruise, and tip would be idle).


I'll tune it again next weekend and post back with my findings. Thank you guys for hanging in there with me.

Chevyz2882

WHats your Fuel Pressure going to the Carb, I kind of had this problem, and it was because I had too much fuel pressure.

GuitarJunki17

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I had it at 6.5, but dropped it to 5.5, as recommended by the manual.

GuitarJunki17

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Well guys, I went all out and tried the richest possible setup I could with my calibration kit. I started at point #1, and went all the way to point #29. To get to this point, I changed both primary jets and metering rods. The secondary jets (.110) haven't been touched yet.







Still have the same problem, falls flat on it's face at WOT, although it's not as bad as it used to be. Also, the spark plugs are not showing any signs of charring at all. They essentially look brand new (STILL lean?)


BUT, I have another kicker here:

When I drive it with the stick in D, this is how the car runs. HOWEVER, if I run through the gears manually, the power and throttle response is there...not as much as it should *theoretically* be, but it is there. Transmission has a fresh rebuild on it 2 years ago, and ran perfectly fine prior to this swap. (and remember I have the geometry correction bracket, so that shouldnt be an issue.)


Still think it needs to go richer? I've maxed out my tuning options with this tuning kit guys, so I'll have to buy the new jets and rods separately. Do you think that the stock secondary jetting is just not enough (I.E. when I get on the throttle, the secondaries open but fuel is insufficient?)

77monte

.. What springs are under the rods? what color? and i highly doubt that going that rich is necessary.. what is the altitude at where you are located. i have one car at 5200 ft and runs flawlessly and the other tuned at 1200 ft and both are fine.. in fact i went the other direction and went a step or two lean on both.. then used silver springs under the rods. i think i have one near 5 and the other is like at 17.

GuitarJunki17

iTrader: (1)

The 8" springs are under the rods (silver, as recommended by Edelbrock's tech staff). I'm moderately close to sea level where I live, right near Trenton, NJ (central).

See, the thing is that I have actually already gone one step down, just to be safe first, to 17, and that did absolutely nothing for me, even tried a few different step up springs as well.


What cam are you running monte? And also, as you get higher with elevation, do you go leaner or richer to compensate?


I should just suck it up and get a wideband sensor. Would one like this do?
http://cgi.ebay.com/ebaymotors/Bosch...spagenameZWDVW

The thing with that one is that it has 5 wires, so how would I get it to run into one really tiny wire from the gauge (it's like an 18 gauge), and would THAT be accurate with your run of the mill $30 AF gauge?

urmomshot77

Well if your having good power down low, then the primaries are probably perfectly fine at stock setting #1 or the step up to #11 at most. Id say you should swap the primaries back a little closer to stock, and up those secondary jets. damn man i hope you get this figured out, because ive been following your thread for awhile. Keep posting what you find out.

GuitarJunki17

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I'll mess with it tomorrow morning and see what I can do. I think I'm gonna double check the cable travel for the tranny kickdown too.

Good to know that I am aquiring a fan base here, haha. Although I'm sure that there are a few guys that sigh and shake their heads when they see a new post with my name on it...but I don't blame them, this really truly is getting annoying at this point.

If this doesnt work out, next weekend I'm gonna toss on my buddies 650 Demon, from his Chevelle motor that spun a bearing, and see what that does. It's tuned for his setup, which is nearly identical to mine, just different brand heads, and a camshaft that has a slightly lower duration.

77monte

The cam's i run are different for both cars.. The monte i run the old school 270 magnum and the formula i run the Comp 274 XE

dimented24x7

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Just out of curiosity, what happens when you roll into the throttle? Does it do ok, and then puke once the throttle is fully open?

dimented24x7

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That type of wideband oxygen sensor needs a stand-alone controller. In order for the sensor to report accuratly, its temperature has to be carefully controlled and its output is also much different then a narrow band stock O2. Innovate motorsports makes an ok setup. Ive had it for the past few years and its a very handy tool.

77monte

Well at this point i suppose i'd start messing around with the timing. I'd start bumping it up a couple degrees and see if it starts improving... Have you mapped out the advance from the mechanical timing? It might be coming in way slow for this combo. Maybe throw a lighter spring on one side of the weights and look for improvements. I have mine coming all in really fast.. probably 2600-2800 rpm and its all in and total timing is around 36 degrees... Having the vacuum advance hooked up to direct port vacuum also helped me out a lot.. and overall having a 3200 rpm stall in the monte helped out a ton too... i get better times by just sitting at idle at the lights and just nailing it on the third yellow, rather than the usual footbrake stall... plus cruising in first gear and at 15 -20 mph i can still light up the 255 70 15's.. this is in a car that in street trim weighs around 4500 lbs too and still around 4300 at the track ( with me at 195 )..

Here is a tip for timing. I found that when i was checking mine that i had seen it sitting at like 12 degrees at idle. Well i figured that was ok and went with it. Then after going through some information and my dad i discovered that even though my idle was only like 750 rpm i rechecked it differently. This time i turned the idle screw down until it was running way slower ( of course vacuum advance unplugged ) and found it was only at like 9 degrees.. so the mechanical was already advancing before and giving me a false reading before... i reset it up to 12 degrees and it ran WAY better.. though in Phoenix it didn't seem to like extended periods of running in the 110+ degree weather and found that 14 degrees was great..it ran even better and got rid of some annoying slow speed problems i was getting after running for 30 mins or longer in heat.. I've had no detonation problems and it complemented the carb tuning greatly.. I hope that maybe this will help you to look in other areas to find your problem.. If it makes you feel better its taken years for me to understand what was wrong and how to make it better.. plus its helped cut easily .5-.7 of a second in the quarter. Next for me is to maybe play a bit with total advance and look for more power. I want to get back to the track and see if enlarging the secondaries is going to help my top end mph and hopefully some of my weight reduction i'll hit the 13's in my battleship of a car.

GuitarJunki17

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Thank you for your insight. I kind of ruled timing out at first because I thought "well since it's at 12 it has to be right". But then again, I got a ProComp distributor, and I know that their products are either hit or miss. I'll try this out and see what happens and if that does nothing, I'm gonna go ahead and slap my buddies Accel distributor in and see what happens before I borrow his 650 Demon and see if I can rule out timing as an issue.



Oh and Dimented, thank you for clearing that up for me. Something like that may just be my next investment.

rjt76

"Brodix IK200 Aluminum Heads" those are some decent sized heads for sure.
put your ignition timing base at idle 20 degrees. put 16 mechanical in the mix for 36 total (I would personally lock it out at 36 degrees and test drive the vehicle.) i bet you would be thrilled with the results. this will probably fix your problem. it sounds as if your timing curve is slow to respond. with those giant sized heads on a mild 350 this aggrivates the problem. with that cam what rpm is the power band for? are you sure everything is matched properly? it gets alot harder to tune when stuff does not match perfectly. this is when you need to start really understanding the suggestions that are given to you.

Tech @ BG

Your cam profile is most likely going to want more than 12 degrees intial timing. You're probably going to have to be between 14 and 16 degrees initial for optimal performance. Now the timing isn't going to fix the top end performance, but you've got to have everything right to get optimal performance.

GuitarJunki17

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The powerband of the cam is 1600-5400. I know I know, I should have a cam to at least 6000, but remember, this was originally going in a TPI motor, and I figured, even if I'm missing out on 600rpm, it should be fine for now until I can find the time to put a better cam in.

GuitarJunki17

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Update:

Well guys, tweaked the timing like you suggested, and still got nothing. Oh yeah, plugs are still crystal clean too, zero soot...indicating no rich.

Last thing I can think to do is borrow my buddies distributor and demon carburetor off of a combo that is very similar to mine and see if either of those solves the problem.

Can anyone give me a product number for the throttle bracket needed for a Demon/holley carburetor to link up to a 700r4 tranny?


I'd like to get this bracket and try this out before I go to the Carisle Swap meet in PA next week. If it's the carb, I might just buy a holley there, rebuild it and sell the edelbrock because this is ridiculous at this point.

I literally cannot think of what else could be causing this. I mean the swap is so straight forward, I know I have fuel, I know I have vacuum, I know I have spark, it's just not working, and edelbrock isn't helping out too much. They say to wait 24-48 hours for an email response but it's been 168 hours and I got nothing.

GuitarJunki17

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Well, I got off the phone with Edelbrock and they are telling me that this carb is the completely wrong carb for my type of combo =/. I'm gonna try and sell this and just pick up a holley at Carisle. I hear that people hate the secondary system on the Edelbrock carburetors anyhow.

It's been fun guys but I guess this carb is just not for me.

GuitarJunki17

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I know that there were those of you that were interested in what my outcome was, and I figured I'd let you know that I am finished finally! I made an update link here

https://www.thirdgen.org/forums/carb...d-finally.html