I will try to keep this short and to the point.
I have a 305 CC QJet with some minor modifications as you can see in my signature.

Problem: Engine will not run good.
Symptoms: Black soot in exhaust
Exhaust smells very rich
White smoke
Will idle @600-900 rpm for 10 or 15 min and when put in gear it will stall. Will not start after that for 1 day.
Next day it starts all over again.
SES light is illuminated but will not give me any codes when grounded.

Tests done: Spark test=Good (New everything, including ECM)
Fuel check=Good (New mechanical and small electric)
Carb=Brand new rebuilt (Seems perfect)
Vacuum Check= can't really get it running long enough to find out. I do not hear anything obvious. Replaced all tubing for vacuum and emissions on top of engine, including Charcoal canister and canister purge valve.


I've been working on it for more than a year now and am really frustrated. I am willing to try anything.

 

Black smoke=fuel

White smoke = steam = coolant

If its burning white, you have some water burning. It could definately make the engine stall.

 

Would this cause black soot in my exhaust?
I backed it out yesterday and an unused O2 plug fell out of the new catalytic converter and black soot/powder was all over my floor. I reinstalled the plug and cleaned up the soot

I did replace the Cyl heads with WORLD S/R Torquers. (6 months ago)
I did initially have a coolant leak and coolant in the oil.
I Retorqued the heads and changed the oil 3 times to ensure I got all the contaminated oil out of the system.
I have seen no coolant in the oil or oil in coolant since then.

 

You are definately running rich with the soot you are talking about, however, some black soot is normal. White smoke is definately coolant. You may want to look into that. If you have had problems with the head gaskets in the past, its always a possibility.

 

Just remembered...
A couple of weeks ago I got it running for about 15 minutes and checked the timing and wanted it to run for a while.
I was piddling around the garage with the car backed into the drive way.
After 15-20 min I heard her stumble and looked to see steam coming out and she was over heating. Before I could get to the key she stumbled and died and steam and coolant were everywear. Primarily coolant was coming out the overflow reservoir and bubbling. The temp guage was at 225 and I noticed the fan was not on.
I let her cool down and found the fuse for the fan was shot. I replaced it. I have not see the fan kick on since then either come to think of it.

 

It all adds up. I wouldnt say for sure that is the problem, because I am not there to see it. But, with you having issues with the headgaskets, the overheating, and white smoke coming out the back, it sure seems suspicious.

 

Blown head gaskets?

Can I just retorque them or should I replace them?

 

I'm not trying to bust on you but I think what you need is a plan. You just mentioned that the cat/con is new but you (I think) live in a state where emissions are not a problem. Maybe that money could've been spent elsewhere. What happened to me is that at some point I needed to decide whether to replace all of the ($$$) computer stuff or go to something a little more manageable. I ended up removing the computer (and the endless wiring that went with it) and going to an earlier Q-jet and HEI, both simple and very functional pieces (the engine dyno'd the same as it's factory rating but with a slight increase in torque BTW).
Right now, you're going to need to do a compression check and see what the problem is, the 305 is about as dependable as a rock (makes about the same HP unfortunately). I'm thinking head gasket. Which means the head has to come off, get shaved and reinstalled. Since the head is off it might be time for a set of roller rockers. (if you go 1.6 you'll have to elongate the guide slots in the head, especially after they're cut). You might find someone to do a little bowl work on the heads, these are simple things that you can either do yourself or have someone do that are reasonably inexpensive, and offer noticeable gains.
Make sure the engine functions correctly (like fixing the fan) checking plugs and wires and search this websight for tech articles.
But first..decide what you want to do with the car, maybe spending big $$ on the 305 is not the answer and now is the time to build a 350. Whatever you decide, figure a budget and add another 25-30%. That should get you headed in the right direction.

 

Cat replacement was $90...no big deal. Was very loud with out it. South Carolina does not have emissions tests.
I have no desire to pull everything and switch to non CC. I am only using car for fun weekends, going to softball games etc.
It is a brand new set of WORLD S/R Torquer heads. So they flow pretty well already.
I did upgrade the Cam and pushrods etc. but stayed with 1.5.
All plugs , wires, dist, HEI cap were upgraded.
I have read every tech article on this site.

I just need to get this (will not run) problem fixed.
The compression check is probably my next step to determine if the Head gaskets are blown...correct?

Thanks for the input.

 

You mentioned a New/Rebuilt Q-Jet. Did you set the float level when you installed the carb? Did you perform the rich/lean stop MC solenoid adjustments? Did you set the TPS voltage?

You cannot simply bolt on the new carburetor and expect it to run. Chances are that the adjustments were set to the mid-range when the carb was assembled, and you have some tuning to perform.

As for the apparent coolant leakage, a cylinder leakage test would be better than a compression test. You would actually be able to observe the bubbles in the coolant, or hear the leakage with that test. A cooling system pressure test would be best to determine if you have head gasket leakage.

 

Leak
Down
Test.

Been covered a zillion times. And as mentioned by my elder above, carbs aren't really plug and play, you do need to make adjustments.

 

[QUOTE]Originally posted by Vader
[B]Did you set the float level when you installed the carb? Did you perform the rich/lean stop MC solenoid adjustments? Did you set the TPS voltage?

No, no & no. The instructions that came with the carb said nothing about those things and I don't remember my Haynes manual spelling out those things either.

Can I ask you to elaborate?

I want to learn but I am teaching myself and learning the hard way.

 

First off. lose the Hayne's manual and go with Chilton's, Motor, or IMO the best, a Mitchell manual.
Yes. Actually the leakage test is probably the best way to go, but the Compression test is a good start.
Have you done any diagnostics?

 

None to speak of.
I can do a spark test.
I bought a vauum tester. Car has not run long enough to really use it yet.
I have learned to check the ALCL to get the SES codes.
I am handy with a voltmeter and can do timing with my new timing light.
I am literally learning as I go.

 

Well to be honest, it's tough to explain some of this over the net. There HAS TO BE some gearheads in Spartanburg that can walk you through it.
Somebody, someplace makes a chemical that turns color if it's introduced to combustion, try NAPA. You put it in the radiator and run the car for a few minutes.
How's the oil pressure?
Is the oil the consistency of chocolate milk?
If you do a compression test remember to remove all of the plugs, open the throttle blades to WOT,(and make sure the ignition is disconnected) . Crank the engine until you get 3 good "hits" on each cylinder.
This can tell you if you have a leaky head gasket, unfortunately it won't tell you if it's a gasket, cracked block or head.
I have a question for you, your car has some major mods, did you do them or someone else? The reason I ask this is because you say you're learning as you go, and I'm trying to figure your level of expertise.

 

I have done everything myself. I really enjoy working on the car and I am pretty mechanically inclined...just uneducated in automobile specifics. I am more than a weekend mechanic but no formal education.
This car has alot of sentimental value and I want to do all i can before i take it to a Pro.


The oil pressure seems to fluctuate from normal to low but could be better. I am sure the guage on the dash is not entirely accurate.

I have checked the oil several times due to not torqueing properly the first time.
I have not seen any more chocolate milk oil since then.

I am coming to the conclusion that I could have a blown or leaking Head gasket, which is causing the white smelly smoke and soot in the exhaust. It probably will not start after a short time because the plugs are then wet.

 

OK, as I recall the factory "idiot light" comes on at only 7psi so if the pressure is higher than that the engine should live. (that's 7psi at idle not at 6500rpms).
I'm thinking that not torquing the heads properly the first time is biting you in the butt. Some people retorque the heads, I don't. I've used shim gaskets and composites and have never had a problem with either.
You'll need to address the rich condition at some point. it's probably better to try that now and not after you pull the heads.
I'm not that great on computer carbs and they were relatively short lived.... try these guys:
http://www.jetchip.com/
http://www.edelbrock.com/automotive/index.html

As I see it, the heads are definately coming off no matter what.

 

Yea...I learn the hard way sometimes. Its ok, at least it is not a daily driver.
Thanks for the input.

I will update you when I yank the heads.

 

The internet is amazing when you want to find things...

A “Leak Down” test pinpoints where you are losing compression and exactly how much before you open up your engine.

The test involves a special gauge and adding compressed air to measure the percentage of leak in the cylinder. One face of the gauge measures the pressure of the compressed air that you are forcing into the cylinder, and the other face measures the percentage of this pressure that is being lost. There is a **** on the gauge that lets you control the pressure going in so you get even results.

There are many manufacturers of these gauges and they are available at just about any auto parts house. Depending on the particular “Leak Down” test gauges you get, the actual test will go something like this:

Take out the spark plugs.

Bring each cylinder to TDC (top dead center) so that all it’s valves are closed.

Screw the gauge adapter into the spark plug well and connect the gauge. The gauge has a fitting to connect the extender hose to the spark plug well, and another to connect the air hose.

Apply the compressed air and modulate the **** to get a steady reading
from both faces on the gauge. Use the same pressure on all cylinders.

LISTEN to where you can hear the compressed air.

At the crankcase: Remove the oil filler cap. If you can clearly hear
a whooshing/howling by listening at the oil filler cap, you're losing
compression through the rings.

At the tailpipe: It is your exhaust valves if you can hear it (or even
feel puffs on your hand) at the tail pipe.

At the intake manifold: It is your intake valves if you can clearly
hear a whooshing/howling by listening at the throttle body/intake manifold.

Repeat steps for each cylinder.

If the results are inconclusive, it could be a blown head gasket. Symptoms of a blown head gasket are: reduced power, white or blue smoke out the tailpipe, oil in the coolant or coolant in the oil. You can check for a blown head gasket by removing the coolant cap and watching the coolant level when you add the compressed air. If it rises or you see bubbles, you have a leaking head gasket.

... Or you could just pressure test the bloddy coolant system.

 

........and then you pull the heads

 

Thanks Red Devil, you are a real asset to this site. :hail: You would think that info would be available somewhere on this site, but I could not find the step by step instructions. I appreciate your willingness to help.

Anyway, I have some work to do, I will update so others will know what to do in case this ever happens to them.

 

TD,

Yes, the Ruby Rascal is really quite an ***... oh, never mind - It's already been said. (Hi, Red!)

RD has outlined the rudiments of a cylinder leakage test. If you are mechanically inclined, but are short of a leakage tester, you can purchase a decent one for about a hundred bucks, or manufacture one of your own for about half that. Either way, the test is the same, and results are a lot more revealing than with a compression test.

However, in reading your previous posts, it seems that you are creating your stalling problems after warmup. That could be consistent with a leaking head gasket. Increasing coolant pressure after the engine warms up would tend to force coolant through any openings. If you want to try to perform a few more tests and adjustments related to the other problems, or just verify that you have a coolant leak, you might be able to keep the coolant in its place by removing the radiator cap before the engine warms up. This would prevent any pressurization of the cooling system and minimize any coolant in the chambers. If this works, you will have nearly proven a coolant leak somewhere. That doesn't necessarily mean a head gasket, but could also be a problem with the intake gaskets, intake manifold itself, porosity or cracks in the new heads, and cracks in the block.

The fact that no coolant is appearing in the oil after the retorque is a good sign, but you may have only minimized the leakage and not eliminated it. If the lack of pressure in the cooling system allows the engine to run longer without creating white (coolant) smoke, you may have an opportunity to set up the carburetor before you remove the heads, if you are so inclined. It may also keep the plugs from soaking up coolant and allow restarts after shutdown.

If/when you're ready for an outline of Rochester E4ME adjustment procedures, let me know. I can send or post them.

BTW - We're ALL learning, and frequently, the hard way. Don't feel like you're alone in that.

Eventually, you may learn that you need a couple more small tools for your set when you decide to set up the carburetor properly. Just another excuse to go shopping and get more experience.

And don't just toss that Haynes manual. While it isn't an all-inclusive repair guide, and lacks a lot of detail and information, it's better than nothing. It's at least a good place to set your beverage so you don't make a ring on your workbench or fender.

 

Vader,that makes total sense to me about why it would be stalling after warm up. Then again I've thought I had it figured out several times only to be proven wrong. Is the stuff Blacksheep mentioned worth a try to see if combustion exhaust and coolant are mixing?

I will definitely try to test the carb out before yanking the heads again.
I would like to confirm the carb is good and also tuneable.

When I do tear down to the block again are there any Head gaskets you would recommend to build it back up?

I would love a good set of instructions for the QJet when you get the opportunity. It seems to be terribly rich.
I would like to tear down the old carb (eat the core charge) and rebuild it just to learn about those little buggers while I have the opportunity.


BTW ...I saw several posts Red has made on other threads and knew what I was dealing with...there is one in every crowd.
He will learn someday, it's not necessarily what you say but the "basket" that you bring it in.

 

TD,

Not in any particular order;

Red Devil has quite a lot of experience, ability, and a gift for explanation when necessary. He also tries to keep the tone pretty light, and is sometimes misunderstood in attempts at a friendly jest. Don;t assume too much. He'll bend over backward to help you out (and has the skills to help effectively) just as long as you don't try to bend him over. He and I go back a few miles, and I can get away with a jab like that on occasion. I know he'll get me back as soon as I'm not expecting it, and I've earned it.

Next, and in reference to the head gaskets, I have a little experience with World S/R Torquer 305s. I had a couple conversations with the World Castings engineers and a sales person about their suggestion for head gaskets. Their instructions recommend a stock set of head gaskets for a SBC 350. My conversations revealed that they selected this design because of the slightly larger valves, and need for clearance at the deck for their chambers. They made the selection after reviewing the available choices. I questioned the selection, primarily becasue the larger bore gaskets would decrease compression and allow potential carbon pockets to form. The area available for sealing would also be diminished with larger bore gaskets (sound familiar?). I had suggested using GM head gaskets for the 305, and had trial fit them, emailled photos, and got their blessing.

Here's where it gets interesting: Stock GM parts (gaskets included) will frequently be upgraded to the latest standards and revisions, and maintain their part numbers. The stock 305 gaskets that you'll get today can be substantially different than the gaskets that originally came with your engine. As a result of GM casting more head variations, fitting them to later blocks, and materials improvements, small changes are made in rhe parts. All subsequently manufactures stock parts would have those revisions. Compettitive replacement parts are often reverse engineered based on the original design, and seldom undergo these revisions. I compared a set of FelPro SBC 305 head gaskets and could see that there might be a minor clearance issue. The revised chamber seal area of the stock GM gaskets had no such problems. I used the GM gaskets with no problems, which resulted in slightly more compression and lower potential for preignition than most other S/R installations that followed the World instructions to the letter.

When you're ready for "The Book", let me know. I'll send you a copy.

 

Vader is right on concerning the head gaskets, They also vary in thickness and if you look on some of the technical pages for the mfg, it shouls list both static and compressed heights. You can use a thin gasket to bump up the compression (and back in the 60's some of the car manufactureres used 2 gaskets to lower compression for the street) However, there are issues with this, because the thinner the gasket, the straighter (flatter) the head/block has to be. In other words, there are better ways to raise compression.
Try NAPA part # 7001300 for the block test kit.

 

TD, don't believe a word he says. Let me tell you about this Red Devil guy. He's a dick, an *******. He doesn't know jack - he drives a damn mustang among other things. He does have an ability/gift - to **** people off. Has some experience at it too. Don't believe a word he says. Total troll know-nothing. Really. Who you gonna believe, the guy that rules down here or one of his minions wearing a glorified pop can for a hat?




Thanks V, you did what is rarely done, got me to blush, though I doubt I deserve any of the kind words. I always think I'm the stupidest smart person people will ever meet. And I have a bit of an... um... rough edge to me to boot.

TD, you can use a coolant pressure tester to see if pressure will hold as well. Both the testers can be rented at various places, if at an auto parts place you can rent them for free.


Did I mention that red devil dude is a cheap bastard too?

Here's more instructions found floating around:



Before beginning the repairs, conduct a pressure test to ensure that there are no additional leaks that were overlooked in the visual inspection.

The pressure tester has an adapter on the end of the hose that connects to the radiator in the same place as the radiator cap. Install the cap and tighten it down securely.

The pressure tester has a gauge with color bands indicating the pressure levels that are appropriate for specific vehicles and cooling systems. Your radiator cap should indicate the appropriate pressure for your system. You can also get this information from your vehicle's owners or service manual. [Let me cut in and say that IIRC (and that’s a big IF) ours are 16 lbs.]

Our project vehicle had a 13-pound system, indicated by the blue bar on the gauge.

With the tester connected, increase the pressure to the cooling system -- using the hand pump -- until the needle on the gauge reaches the appropriate bar.

Leave the tester on the system, and check it in about 5 minutes. If the system is sealed properly, it should hold pressure, and the needle will not drop significantly. If the system has a leak -- as ours did -- the needle will quickly drop down out of the acceptable range.

With pressure applied using the pressure tester, an additional leak was identified in the area of the bypass hose that hooks to the water pump.

 

See...I knew all that info was in there just dying to get out!
I think I may blow Christmas this year and just work on the "muscle car" as my kids call it. Well, my wife may not be to thrilled about that.

I used FelPro for SBC 305 the first time.

I will first get the coolant pressure tester and do that test.
If it will not hold the pressure (which I would be shocked if it did) would I be ok to retorque them first or should I just yank the whole sh'bang and replace the gaskets?

If I replace the gasket exactly which one should I look for? (GM head gaskets for the 305?)

Any idea what ballpark my compression should be right now with the mods I've listed?

 

Pull 'em and go the same route Vader did.

 

Ok
Got coolant system tester.
Applied 18psi and a little leak developed at the thermostat hose and at the top radiator hose. Snugged both up clamps and the leaks stopped.
Repressurized and the pressure dropped 5 psi in less than 2 minutes. I see no visible leaks near the head gaskets and no other leaks at the hoses.
Must be leaking internally...as suspected.

Looks like blown head gaskets...correct?

 

Steam coming out the exhaust, cooling system dropping pressure with no external leaks, yeah I would say you have nailed it. If it were me I would pull the heads. Just be glad you arent leaking massive amounts into the oil.

 

After 45 min the pressure seems to have stopped dropping and is @ 10psi

It is nice to have a laptop in my garage with wireless internet set up!

 

have the head decks cleaned up. better to be safe than sorry.

 

Driver side fixed. Gasket seemed fine.
Found an external leak on Passenger side when I did a second test. It was on back side next to fire wall. Looks like gasket is blown out. Hope to do pass. side this week.

 

Glad you found 'em. Did you use the same gaskets Vader recommended?

 

Yea, I printed the post off to make sure I had the right ones.

 

Ok...2 straight days of work and I finally got the Pass. side buttoned up.
I put the new gaskets and the Manifold back on and secured just the coolant system and did another pressure test.
Pressurized up to 17psi and after 5 min it was still at 15 psi with NO visible leaks.

Does this mean it worked?!?! :lala:

With it perfectly quiet in the garage I can hear what sounds like an air leak (no coolant anywhere) somewhere on the front-top...maybe thermostat housing. I torqued those down to 20lbs...I don't want to strip out the new manifold.

 

Hey Vader,
Any chance you can enlighten me. I will be ready to set up this carb before I go any further.

Thanks
Thom

 

You may have a slight leak somewhere, I'd worry about it if it manifests itslef as last time.

Go ahead Vader, post a book.

 

Hopefully, the reman carb has been assembled correctly. We'll have to presume that, unless you want to disassemble and check everything. Even at that, there are a few things that need to be checked and adjusted for each application. Float level, float drop, main jet size, secondary metering rods and hanger, and choke pull off must be set according to the individual application, since each type engine runs best at different settings.

To check the main jets, float level and float drop, the air horn/fuel bowl cover must be removed from the carburetor. Here's a brief outline, with a few other pointers for setting it up:





FLOAT CHECK

1. Remove the air cleaner and cap any vacuum lines that were disconnected;
   
2. Unplug the Throttle Position Sensor and enrichment solenoid connectors;
   
3. Remove the choke pull-off actuator and linkage rod (25 & 28);
   
4. Remove the secondary metering rod cam follower (10) and metering rods (9);
   
5. Remove the choke lever screw and lever, and the linkage rod (29, 30, & 31);
   
6. Remove the air horn screws (5, 6, & 7) and the two front carburetor to intake bolts;
   
7. Carefully lift the air horn (1) off the carburetor body. As you do, pivot the air horn to allow the accelerator pump linkage rod to be removed from the top lever (3, 69);
   
8. Hold down the float hinge pin (57) and simultaneously hold the front end of the float (56) closed against the inlet needle and seat (55), to raise the float to its maximum position. Verify correct float level by measuring the rear edge of the float to the top of the carburetor body with no gasket in place. Gently bend the float tab to raise or lower this setting to the specification;
   
9. Replace the gasket and reassemble the carburetor, being careful to properly align the metering rods, pickup tubes, and TPS actuator plunger;
   
10. Reconnect the hoses and electrical connectors;

TPS ADJUSTMENT

1. Start engine and allow it to reach normal operating temperature;
   
2. Set engine timing at the specified RPM;
   
3. Set base idle speed with the A/C off and idle speed solenoid disconnected;
   
4. Turn off the engine;
   
5. Insert the probes of a digital voltmeter in terminals ‘B' and ‘C' on the TPS connector (center and bottom terminals). You may have to insert a paper clip or similar object into the rear of the connector to make contact;
   
6. Turn on the ignition but do not start the engine. Read the voltage of the TPS. Remove the top plug (19) and adjust the TPS screw (18) to obtain a reading of 0.48VDC across the terminals.
   
   NOTE - If your meter probes are reversed, the reading will be -0.48VDC. The important factor is the number.
   
7. Replace the hole plug in the adjustment screw hole when the position is set.

MC SOLENOID ADJUSTMENT

• Connect a dwell meter or oscilloscope probe to terminal ‘B' on the enrichment solenoid connector;
  
• Start the engine and allow it to reach normal operating temperature. Start the engine and reset the base idle if necessary. The dwell meter reading should vary while this is occurring, or the oscilloscope square wave frequency (pulse length) should vary;
  
• Set the parking brake, block the drive wheels, and place the transmission in DRIVE for an automatic car, NEUTRAL for a manual car;
  
• The dwell meter reading should fluctuate between 10° and 50° on the 6 cylinder scale, the oscilloscope should indicate a 15-85% duty cycle. Adjust the idle air bleed valve screw (12) in 1/8th turn increments to obtain a dwell reading between 25°-35°. The optimum setting is 30° (50% duty cycle), so get as close to this as possible. Adjust the screw only a little at a time and allow the system to react between adjustments;
  
• If the desired reading is not attainable through this method, the idle mixture screws will have to be adjusted (87). This will require removal of the carburetor and cutting the throttle body away around the steel plugs. Then reinstall and adjust the idle mixture screws evenly , then adjusting the idle air bleed screw as described above to obtain the correct readings.

A "dwell" meter is basically a duty cycle meter that is graduated on degrees of distributor rotation for an engine. In Kettering (breaker point) ignition system terms, the duty cycle is the amount of time that the circuit is on (points closed) versus the amount of time the circuit is off (points open). The meter face is graduated in degrees of distributor rotation. A point dwell angle of 30° on a V-8 engine is basically a 66% duty cycle, or ON time versus OFF time. One cylinder fires every 45° of distributor rotation (90° of crank rotation), so if the points are closed for 30° of that time, they are open for 15° of that interval. 30° ÷ 45° = 2/3, or 66%.

A six cylinder engine is similar, but one cylinder fires every 60° of distributor rotation (120° of crank rotation). Typical specs for ignition point dwell on a six cylinder are 33°, and on a four cylinder engine 40° is common.

In terms of the mixture control solenoid on your carburetor, it is basically the same thing. The dwell meter is used to determine the amount of time the MC solenoid is ON versus OFF, or duty cycle. Since most automotive technicians have (or had) a dwell meter, the specification is presented in terms of dwell degrees. In reality, the measurement is the duty cycle percentage of the solenoid, but the common dwell meter is not graduated in those terms. Remember that 30° on the "V-8" setting on your dwell meter really means 66% duty cycle, and 45° would equal a 100% duty cycle.

Typical instructions for setting the solenoid are to set the meter on the six cylinder scale and adjust the "dwell" to an optimum of 30°, or in reality a 50% duty cycle. This means the solenoid is ON an equal amount of time that it is OFF. This is the optimum setting for fullest range of control by the MC solenoid.

If you don't have a dwell meter, but do have an oscilloscope or better quality DMM with a duty cycle scale, just set the MC solenoid for 50% or as closely as you can get it. The typical instructions indicate that any reading between 10° and 50° and varying is acceptable (15-85% duty cycle), but "acceptable" isn't good enough for most of us, or we wouldn't be here.

 

(Since posts are now limited to 15,000 characters, I guess I need to break this up a bit.)


Once you have it running correctly in stock form, you can begin the power tweaking and tuning.


From our friend, Ed Maher:

Tuning for Performance with your Computer-Controlled Quadrajet
Here for your digestion are some easy mods, with brief explanations, that you can make to any computer controlled Quadrajet. They require only simple tools, and most are free. If you have any questions, or need some advice, email me. -Ed Maher

Setting the Air Valve (AV) tension
The AV is the flap that covers the secondaries of your carb. It opens up when airflow through the secondaries demands it. Decreasing tension on it has 2 main benefits. It allows the AV to open faster, giving you full power sooner. It also allows the AV to open more easily with airflow, giving you the possibility to make more total power. It is held shut by 2 things.

First by the choke pull-off diaphragm (which is on the front pass. side of the carb.) When the engine is running , the choke pull off keeps the AV closed by pulling the linkage via the rod that connects them. When you go to/near WOT, the choke pull-off pulls out(due to the loss of manifold vacuum) and allows the AV to open. The pull-off generally releases slowly, slow enough that even with no AV spring tension you shouldn't get a bog. The rate at which it pulls out is not adjustable with the metal can pull offs our carbs came with.

The AV is also held shut by spring tension, and that is adjustable. To adjust it, you will need a small allen key (either 3/32 or 5/32, i forget) and a small flat screwdriver.

(**note: it is possible that instead of an allen key you will need a small torx bit, but they are rare.)

Now, here you go:
1.Look at the pass. side of the carb (with the air cleaner off)

2.Observe the linkage on the side of the AV. Through the slot you can see a small flat screw. That's the one you need to adjust.

3.To adjust it you need to loosen the setscrew, which is on the underside of the lip of the airhorn. The setscrew is where the allen/torx bit comes into play. Loosen it only enough that you can turn the adjusting screw.

4.Turn the adjusting screw counter-clockwise until the AV flops open on its own. Now slowly turn it clockwise until the AV just shuts. That is 0 tension. If you were setting it to factory specs you would then proceed to turn it down the specified turns (usually 1/2-1 turn). Instead, tighten the setscrew and go drive.(**note: You may have to hold the AV rod to the pull-off out of the way while you adjust the tension. You can also remove the pull-off, but that is really excessive. If you exercise some common sense, it isn't hard to figure out how to hold everything.)

5.With your car fully warmed up, come to a stop and then nail it. Did it bog? If it didn't, consider yourself done. If it did, then there are a few ways to proceed. First ask yourself if you have a fresh tune-up. If not, what are you doing making performance mods when your basics aren't even done. Shame on you. Also, be sure your choke pull-off is working properly. If it is bad, it could cause you problems too. Second, now is a good time to read the next section on changing secondary metering. Finally, if you don't want to change secondary metering (and why not?), you can increase the AV tension until the bog goes away. Go in 1/8 turn increments at a time, and stop when the bog goes away. Do not increase the tension to over 1 turn down or you will permanently distort the spring.

Changing the Secondary Metering Rods and Hangers

1. Look at the top of the carb between the flaps of the AV. Observe the little screw on the hanger.

2. Take that screw out. Most likely you will not own a torx bit small enough to remove it. The easiest way to take it out in that case is using pliers to turn it out. It sounds barbaric, but it works. If you didn't have the proper torx bit, while you have it out, modify the screw for future use. Either hacksaw a slot in its head to accommodate a flat head screwdriver, or file its sides flat so that it is easier to grip with pliers.

3. Lift out the hanger and the rods with it. REMEMBER WHICH WAY THE RODS ARE ORIENTED ON THE HANGER.

4. Swap the rods or hanger or both with what you want to drop in.

5. Drop them back in. They should drop in with no trouble. If there is friction, you probably have the rods on the hanger backwards. Don't start bending the hanger to make it fit until you try reversing the way the rods tips are facing.

Tuning Notes
Here are the basics of rods and hangers. The thinner the tip of the rod, the richer it is (more fuel can flow around it.) The thin part at the tip is called the power tip. The longer it is, the faster you go under enrichment when you floor it. For drag racing purposes, and in general, a longer power tip will give better response and performance. Rods have identifying letter stamped on their sides. The letters are nearly meaningless though without a book on rod specifications. Instead, compare them by sight. If you do have access to specifications, look for thin tips and long power tips (also found by short tapered sections). A great all around set of rods IMHO are the CKs, which are marginally richer than stock L69 rod, but with a longer power tip.

Hangers are identified by the letter stamped into the top of it, the lower the letter, the higher it holds the rods out of the jets, giving you more enrichment sooner. This can be especially helpful in covering a bog going into full throttle, as well as for some extra grunt coming out of the hole.

You can find replacement rods and hangers at a few sources. Edelbrock and GM both stock new units. You could also try poking around in boneyards and swap meets. New, rods should only cost you about $8, hangers about $4. Edelbrock parts can be easily ordered through Jegs (including CK, CC, and CE rods, as well as a good assortment of hangers.)

Increasing Airflow
Stock our carbs are limited to about 600cfm total airflow due to a tab that prevents the AV from opening fully. However, our throttle bores will support 750 cfm, once the AV is allowed to open fully. If you've got a reasonably well-modded car and you think more airflow is in order, here's how to fix that.


1.Look at the AV linkage. Rotate the AV open and observe the little tab on the bottom of the linkage that hits the underside of the airhorn lip.

2.Cut, file or otherwise mutilate that tab off. (*see note*)

3.If you want to get really trick, you could drill a hole in the airhorn casting where the tab hit and put a setscrew to adjust the total opening of the AV. This could be used as a tuning tool, along with different metering rods to change airflow and fueling to suit current conditions.

(*Note: When removing the tab, be careful how much you remove. If you file it down flat, you will definitely get interference with the AV linkage. When that happens, you have to get creative and tweak the rod and/or cut the slot in the linkage longer to allow it to work. If you want full airflow, this is your only option, and if you're remotely mechanically able it's not hard, but i still had to let you know in advance.)

After doing this mod, you will need to adjust the secondary metering to suit. After doing this, my old CK rods/G-hanger set-up was woefully lean. Stepping up to CC rods has put me right back in order.

Other Tuning
The stuff mentioned herein is more advanced and requires you to get into your carb. At this point you definitely should have a manual for your carb, and should have a good understanding of how it works.

Primary Enrichment
If you have a part-throttle flat spot, or feel you just need a little more enrichment, look here. This requires you to remove your airhorn and take out the plug covering the rich stop screw. By manipulating the travel of the MCS, you can make your car run richer/leaner to suit. As longs as you don't go too far, it will still keep low emissions and fuel economy. But under WOT/enrichment mode you would have the extra fuel. Give it more travel and it gets richer, less travel is leaner. Don't go under 3/32 travel though, that would be too lean and probably mess up overall driveability. Adjust this in 1/4 turn increments. I bought a kit with the proper tool to turn it, and a travel indicator/idle air bleed tool for $4 at Pep Boys (ask for a mixture adjusting kit, listed with the rebuild kits for the carb.)

Idle Air Bleed
This is a worthwhile piece to adjust properly too, especially if you have a lot of mods. I won't go into the whole process here (just read the manual), but i will emphasize a few points. By adjusting the IAB, you don't have to mess with the mixture screws as on previous non-computer carbs (unless they are set way off.) By having the IAB adjusted properly, it allows your computer to continuously adjust the idle mixture, keeping your car running clean. Set it with your car in gear if i is an automatic car (have a friend hold the brake.) Adjust it very slowly (in 1/8 turn increments, waiting a few seconds between to allow the car to settle.)

Some other notes....If your dwell at idle won't vary from 10', then your car is either stuck in enrichment mode (bad or maladjusted TPS) or is compensating for a very lean condition (BIG vacuum leak, loose carb bolts, or a bad TPS) Either way, try to establish the problem before going any further.


Thanks, Ed. I knew you weren't just a TPI guy.

 

And just a few random bits of information:


SECONDARY METERING RODS

Tip Length Legend:

• LL: Extra long power tips supply richest mixture starting at 60° of air valve opening.
  Never use in performance applications using greater than 70° air valve opening.
• L: Power tip starts at 70° air valve opening.
  Tip considered to begin at that part of the rod that is within .003" of rod's minimum diameter
• M: Power tip starts at 80° air valve opening.
  Tip considered to begin at that part of the rod that is within .003" of rod's minimum diameter
• M/S: Power tip starts at 80° air valve opening.
  Tip considered to begin at that part of the rod that is within .005" of rod's minimum diameter.
• S: Power tip starts at 90° air valve opening.

 

Incidentally, if you don;t already have them, you'll need these tools to perform the TPS and lean/rich stop adjustments on your carburetor:

http://www.handsontools.com/store-pr...3E_317751.html

That isn't the only place to get them, but I've found that many parts stores no longer stock the tool set since carburetors are so passè these days. I found my sets at Skyway Tools, but there are many vendors.

The important thing is to look for OTC 7667 or equivalent tools for your project.

 

Wow.
I must say I am impressed. This is exactly what I was looking for.
Obviously I have read the articles in the tech section, but it will be great to have this info in one spot.
I am printing this off to keep in my reference material.

BTW, I bought a Chiltons manual to add to my meager collection.

I will do the initial set up and let y'all know from there.

 

First off...There is no voltage going to the MCS. (No clicking & no voltage with the key on)
Does the voltage come from the PROM?

 

The MC solenoid is powered by the ECM. There is an output that operates the MC solenoid when the system is in closed loop mode. I've seen some earlier CCC systesm that operate the solenoid even with KOEO, however.

Make sure you have a voltage supply to the MC solenoid from the ENG CNL circuit, 10A fuse. It provided power to the solenoid, and the ECM output switches the ground of the circuit.

 

I cannot get a code to pull from the ALCL and it is a new ECM.
Could these be related?

The SES is lit but will not flash any codes.

 

That is a possibility. One thing to check is the startup routine. When you first turn on the ignition, watch the SES lamp. It should turn on, then off briefly, then turn back on and remain on until the engine is running.

 

When the ignition is on the SES light comes on and never flickers...just stays lit even after it starts.

 

From what I can recall of the last CCC I worked on, that's not a good sign, but it might not be teh end of the ECM. If my recollection is any good (and it's always suspect) that can occur if there is a load that is not connected, like the MC, or PORT/DIVERT valve for the A.I.R. system, or possibly a sensor that is out of circuit.

You might also be getting the error from a PROM that is not secured in the ECM socket.

 

Nice book.

I had a TBI truck that had SES problems like that. ECU was junk.