The Stovebolt Site Forums The Shop Area The HiPo Shop Carburetion - how much is too much?

I have a built 327 out of a 65 Corvette in my 38 with an Edelbrock 600 cfm carburetor sitting on an Edelbrock manifold. The engine has a Stage 1 RV cam (whatever that is). When I run the engine in the garage with all doors and windows open the fumes are so bad it makes the eyes water. I know it's running rich because I pulled a plug and it was black and slightly wet. Since I've never had a high performance setup like this I really don't know if this condition is normal when the engine idles a lot, or what I need to do to correct it. I don't have any other information on the engine because the guy I bought it from wasn't all that helpful. I don't think he was too happy with the deal.
Thinks for any thoughts on this. Don

38: Sounds as the Carb. is running to rich, need just a little more air mixture. The carb is a good size for that motor. Also the RV cam has a hair more lope than standard holding the exhaust open a little longer on duration. (I believe)its early and I am thinking about something else. Ben

popcorn The Truth is Out There (Sounds like a great setup just a little fine tuning)

38chev Is this a new edelbrock? They claim to be ready to run out of the box but the 2 I have purchased were also running really rich. You can purchase a tuning kit with different springs to adjust the fuel flow. Try edelbrocks web site, u may be able to download a manual.

That size motor should really like that carb. The carb has 2 mixture screws and a center air screw in the front. You may want to lean the mixtures in, then add some air by backing out the bigger one in the center. Beyond that, take a vacuum reading then look into the power valve circuit. I can't recall if that's mechanical on that one or vac. If it's mechanical, look at the needle setting, and look to see if the secondaries are stick open a lil bit. I did se one case where a guy backfired a time or two gettin dialed in and it bent the secondary shaft holding them open and running pig rich.

If none of that works, you may be too low on the lead, or initial timing. Try bumping that forward and see if it helps. You will need to adjust idle speed when it's all tweeked in. Worse scenario, the cam is in wrong. It has been known to happen. Sometimes cams be ground a bit off. That's why good builders use degree wheels to check.

The edelbrock I put on my 327 ran great out of the box, but it was pre-tuned to the performer system, which I have on my engine. If I'm not mistaken, the lopier, more aggressive cams don't have as strong of a vacuum signature, and therefore run leaner than an rv cam on a torque-tuned motor. that would make a carb run great on my engine, but $h*tty on yours.
To tune your carb, start turning in the two idle mixture screws on the front of your carb 1/2 turn at a time. It's important you alternate from one side to the other, to keep them in the same position as the other. Keep going in until the RPMs of your engine drop. This indicates your engine is too lean. Now back the screws out, alternating again, but going only 1/4 turn at a time. The RPMs will climb back up until they hit a plateau. Give each screw one more 1/4 turn, and you should be good. You can do this by ear, just listening to the RPMs, but an accurate handheld tach is a lot more precise. Hope this helps.

My Edelbrock responded well to tuning. Read the book:
http://www.edelbrock.com/automotive/eps_intro.html

and get a calibration kit. It's easy - even I could do it.

Hi guys, thanks to all who responded to my question. Here's an update and a little more info. The carb is not new and out of the box. It had been previously installed on another vehicle but only for a short time. I bought it used. I found out that my timing was pretty severely retarded, when I advanced it the engine ran much better. Also adjusted the idle mixture screws and that helped. I bought a new set of plugs, hotter than the ones that were in there. Will put those in today and see if that also helps. As soon as I log off here I will go to the Edelbrock website and see if I can find the specs on the carb and look into a re-build kit for it. Power valves could be part of the problem so new ones wouldn't hurt. Thanks again, I'm feeling better about the size of the carb for my engine. Don

Ive got one on my 70 w/350. It ran too rich. I got the tuneup kit & put in smaller jets & larger metering rods. It helped a lot but I still cant get the gas mileage I want. They have no power valves as they use metering rods. Different springs come with the kit.
I,m going to change to a Q-jet.

A quick thought: is the carb a 1406 with electric choke? If so is there a good 12v source to the hot side of the choke coil? (and ground tot he ground side?) If it's disconnected, or the power lead run thru a switch of some sort (like an oil pressure switch or something) it might not be getting power to open up the choke blade. This will cause it to run rich as hell, appear to warm up very slowly and the secondaries won't open. (Don't ask me how I know these things.)

Again, if it's an electric choke, check for 12v across the power leads of the choke coil.

hth,

It's a manual choke, but wish I had electric. After installing the new plugs and making some adjustments it's running great now, still somewhat rich, but better. Curious thing though, when I pulled the carb there was oil, some fresh and some old, on the bottom of the throttle plates. It's sucking up the oil through the vacuum system EGR valve I think. Is this normal?
TIA, Don

Do you mean PCV instead of EGR? I hope you're not running an EGR on that motor.

If you mean PCV, then yes, it's normal for some oil to precipitate out of the crankcase gasses that are re-introduced for burning. Shouldn't be a problem, unless it's really drenched...in which case I'd spring for a new PCV valve.

Ray, yeah I did mean PCV valve, don't know where the EGR came from. The rattle ball is loose in the valve so I assume it's working okay and since there's not a lot of oil on the throttle plates I'll also assume that's a normal condition.
Thanks, Don

I have read a number of times that the Edelbrock does not like more than 5psi on the fuel. My friend had several problems with his, including hot restart problems. After much proding, we finally put a gauge on it. 9psi. He couldn't bear to part with his Holly hipo mechanical fuel pump so we put an adj. pressure regulator on it. He called the other day to say the press reg is leaking.
He wants to toss the Edelbrock, I say toss the pump.

As others have said, the 600cfm Edelbrock is an excellent choice for a 327 on the street.

All motors like the timing to be right. That was a good place to start. Fixing that also improved your vacuum at idle, which is a good thing for the carb. Good job! What is your initial advance set at now?

My motor likes 8deg initial, 22deg mechanical, making 30deg total, all in by 2500rpm. And I'm also a big believer in vacuum advance. Is yours routed to full or ported vacuum? If it's ported, try it on full and see if you notice an improvement. (This really smoothed out the "rump" of my last cam. Great for me, other folks like a really racy idle...)

The comment on fuel pressure is right, too. Edelbrock's need a regulator!

If your cam is "too big" (translation -- anything more than stock), you have to be really careful to have the right springs in your Edelbrock. I had very similar symptoms on my motor. If the springs are too strong for your vacuum at idle, the metering rods end up in the wrong position, and dump lots of extra fuel. Springs are so easy to change -- no need to remove or disassemble the carb! Buy the tuning kit at your FLAP. Just pop the old springs out, pop the new springs in. (Don't forget you'll have to reset idle speed and mix, especially if the springs were the culprit!) Made a ton of difference for me. I'll bet dollars to doughnuts this will help you, too.

On the oil you mention being sucked in from the PCV, this is also a common problem on performance motors regardless of carb. One valve cover should have a breather, the other should have your fill cap and PCV. And the one with the PCV should be baffled, so you don't have a straight draw from the rocker arms to the valve.

There was also a lot of discussion on chevelles.com a couple of years ago about which PCV valve to use in performance motors. I'll see if I can find the old threads, and get you a part number or application.

Cheers,
mark.
'51 3100

Mark, thanks for all the excellent advice and suggestions. With my limited mechanical skills I can't answer all your questions. Initial timing is about 10 degrees advance, but don't know final advance. It is a vacuum advance with vacuum supplied from base of carb. I'm not sure about changing springs. Are you saying just replace existing springs with new ones, or are there springs with different rates? Also, regarding fuel pressure regulators, I have a stock mechanical fuel pump, don't know how many psi it's putting out though. I will look in my Summit Racing catalog and see about buying a regulator.
Thanks again and best regards, Don

Edelbrock sells a tune-up kit with different metering rods and springs. The kit is a little pricey for what you get, but it's helpful. It's best for tuning at the drag strip to get your full-throttle settings dialed in. The Edelbrock manual is very good- I follow mine like a Bible. If nothing else, you can pull the rods and springs out of the carb, and if the paint is still on the springs, and the numbers are still readable on the rods, you can compare it to the manual shows as being stock for the carb. You only need a 1/4" drive ratchet and a rag to throw over the mouth of carb- it's super easy on these. I run an RV-type cam in a mild 318, and the stock 1406 set-up was great for me- that RV cam shouldn't be causing you any vacuum problems.

To check final mechanical advance, you disconnect the vacuum line from the distributor, plug it or clamp it off with visegrips, and then rev the engine up slowly until the timing mark stops moving. I like using a dialback timing light for this, but use what you have. It helps to have an extra set of hands for this- one guy on the light, one guy on the throttle.

As for the PCV, check where the valve is installed- if it's a homemade installation, make sure there's a baffle behind it to block flying oil from getting sucked up.

For checking your timing curve, you should have an underhood dwell / tach meter; and a timing light.

Disconnect the vacuum line from your distributor and plug it. Check your timing at idle. This is intial advance, and is what is adjusted by loosening the distributor hold down bolt and rotating the distributor by hand. 10 deg is a good starting point.

Rev the motor up 200 rpm or so at a time, and watch the advance. You get more advance as engine RPM increases -- This increase is called "mechanical advance", and is controlled by weights and springs inside the distributor. When the advance quits moving ahead, it's "all in". The final reading where advance stops increasing is called "Total Advance". You may need to put some extra marks on your balancer to read total advance, unless you have one of those fancy "dial back" timing lights. To figure how much mechanical advance you have, subtract Initial from Total.

The difference between "Full" and "Ported" vacuum is whether the opening is above or below the throttle plates in the carb. Remember that vacuum line you plugged when checking your timing? Put your finger over the end at idle. Got Vacuum? Then it's a "Full" vacuum line, and means your vacuum advance will be active at idle. No Vacuum? Then your line is hooked to a "Ported" vacuum source, and your vacuum advance will not be active at idle. Try it the other way, and see if your idle smooths out a little. Look around -- the other vacuum source should be close by, and have a rubber cap on it.

Are you running points or HEI? Points should have a "ballast wire", which is basically a resistance to drop voltage to the coil to keep from burning the points. This is sometimes lost, or the wrong size, when these old trucks are converted to 12V. HEI distributors should NOT have a ballast wire -- they need a full 12V. The points ballasts are sometimes left in when these old trucks are converted to HEI.

Now that you've got the ignition tuned in, use a tee to connect your vacuum gage to the vacuum advance hose going to your distributor. What? You don't have a vacuum gage? Need one, and they're cheap. Most FLAPs (Friendly Local Auto Parts stores) have them. Let us know how much vacuum you have at idle.

The Edelbrock book is VERY good, and includes a simple procedure for adjusting your idle mix by watching vacuum levels.

The rods and springs on your Edelbrock are hiding under two little flaps on top held down by small screws. Loosen a screw, slide the flap over, and tell us what color the springs are painted. Like Darby said, they're color coded -- If you've got the wrong spring color for your vacuum level, you'll be idling with the part of the metering rod intended for feeding much gas at high throttle. The "kits" are expensive, but they end up being cheaper than buying a set or two of springs, and a set or two of jets, and a pair of rods, while you tune it in.

And remember -- you're having fun!

Cheers,
mark.
'51 3100

Mark, Darby, thanks soooo much for your excellent advice. I have all the tools needed to perform the checks you mentioned, but don't have the necessary time right now. When I'm able I will do as you suggested and then will see how it goes. This really is a great forum with so many helpful and knowlegeable folks. I'm very appreciative as I know others are as well.
Thanks to all, Don