This Is Not Normal....
 

New to me early 70s 400 is throwing what I believe is a LOT of soot out the exhaust. It starts, idles & runs fine except that it does not seem to 'get up and go' when I put my foot in it - meaning that I don't really feel the secondaries kick in.

Has a Holley carb with vacuum secondaries and an electric choke. The choke seems to work fine and drops out shortly after a cold start. Engine runs fine even prior to full warm-up.

Any ideas as to what I should check? Would it be worth it to take to a shop with an analyzer?

Sorry for the upside down photos - can't figure out why they flip after upload....

Do you have a vacuum gauge to check idle vacuum and to check that it's steady also at idle, if so report back with that number?

Black smoke out the tail pipe is from excess fuel and if you see this emission while just driving on the Carbs primary side then it's not likely a secondary side issue, however there are a lot of things on the primary side of a Holley that can make for rich running above idle.

How is the fuel level at idle at the site plug?

I would start off with replacing the power valve if the fuel level is ok which is likely a 6.5" type an I would also do the metering block gasket.


You need to figure out what is making this condition pretty fast because seeing black smoke means the cylinders are getting washed out of the oil that they need ware at a normal rate.

Last but not least your timing chain could be ready to let go which can make for your condition in some respects.

pS, you can rotate your photos in your phone with the controls that appear when your looking at the photo you want to use.

Agree with Steve, you are dumping fuel. I would start with the idle adjustment screws at 1-1.5 turns from full seat. check what jets you are running from stock calibration and ensure the power valve is working. 6.5" is the norm, Holley says it should be half your vacuum reading for starters.

Needle and seat are stuck open fuel is coming up from your vent tube into the system.

Pull the needle and seat assembly tapp it out blow some air through it and put a better inline fuel filter on it.

It could be as simple as the air bleeds being blocked with crud or maybe the economizer (power) valve diaphragm broke. Both are simple fixes.

... I have 14 inches of vacuum at idle, steady.

No sight plugs on this carb.

I'm going to adjust the idle mixture and see what I get. Found a Holley forum article that has you adjust idle mixture for best vacuum. Will give that a try.

meaning no clear plastic plugs... bear with me here I'm just a half turn beyond complete newbie.. :D

a: choke looks a bit closed
b: leak down test should show valve guides
c: using something thicker than 10W-30 ?

get a wideband. it will teach you quite a bit about your engine. just don’t get hung up on hitting a specific afr, use it to measure trends and to see how different adjustments affect your readings.

for instance, you might not want to use your wideband to tune to a specific idle, cruise, or WOT AFR, but your wideband can help you figure out if your engine is particularly rich, say, at cruise but not idle or WOT, etc.

Does it do this all the time?

Or just when the engine is cold and choke is working?

Clay

Check your float level first. With the engine shut off, remove the sight plug and bounce the front fender. Fuel should trickle out when you bounce it. Sitting static, the fuel level should be just barely below or even with the bottom of the sight plug opening. Also try rotating your choke slightly leaner. It may be staying on a touch too long and loading up on warmup.

That carb appears to be a Holley Spreadbore 650 with an electric choke it added. An older design, they are not equipped with the power valve protection check valve. The power valve diaphragm can be damaged by a backfire. You can
field" check the power valve without disassembling the carburetor. Warm up the car to clear the exhaust of any condensation. Have someone rev it (let it drop to idle, rev it and repeat) while observing the tailpipe tip. If you see sooty exhaust or liquid fuel drip from the tail pipe, then a leaking (blown) or out of spec for the engine's manifold vacuum is likely the cause. If the car smells gassy while driving and the tailpipes are always sooty, this is the probable cause.

That carb came from the factory with an 8.5 primary power valve which which can cause a partially opened (enrichened) condition if your engine idle vacuum is less than 15"-17". Pick up a vacuum gauge and check your idle vacuum through a port below the throttle blades (manifold vacuum) and see what you read. Divide that number by 2 and round up to the nearest available power valve size (8.5, 6.5, 5.5, 4.5, 3.5 are standard power valve sizes).

Regarding secondary operation, Holleys are different than Q jets. A Holley carb has only a single set of throttle blades, they do not howl on secondary opening as you may be accustomed to with a Quadrajet (air taking a more torturous path around the secondary air flap and secondary throttle blades and causing the secondary air flap to oscillate).

Properly adjusted vacuum secondaries on a Holley do not induce a snap when opening (which is actually a stumble) but are simply drawn open with a turbine like smoothness so as to be unnoticeable (other than the tire spin lol) as you roll into the throttle. You can check for proper function by holding a mirror at angle over the carb while operating the throttle and observing the secondaries or just watch the secondary throttle shaft rotate as viewed from the side of the carburetor while going to full throttle.

The rate and percentage of secondary opening will vary based on the engine's vacuum characteristics. On some cars, the secondaries may not fully open even at full throttle. Being based on the engine's requirements, full opening may not be required even at full throttle as the engine has already reached its vacuum limit and maximum air flow requirement. This is particularly true when a large carburetor is installed on a small CID engine. On a 400 like yours, the 650 should be pretty optimal for a stock or mild state of tune engine.

If you favor a more rapid secondary opening rate, Holley sells lighter springs that install inside the vacuum secondary actuator (flat-round canister just behind the choke). You have to remove the carburetor to remove the cover plate as the screws are threaded in from underneath "to keep the kids out". It is a very simple modification and some engines can benefit from more rapid secondary opening.

Companies like QuickFuel incorporate adjustable vacuum secondaries through an external screw which adjusts the speed of secondary opening by varying the internal spring's height (tension). Holley also sells a QuickChange cover for the vacuum actuator that allows the screws to be installed from above allowing the springs to be changed without taking the carburetor off.

Good Post, NeighborsComplaint, 8.5" Power Valves are rarely used on any street cars but are used on delivery trucks and power boats where you need a lot of fuel quickly when a higher load is imposed on the engine.

If the OP could post up the stamped numbers on the air horn we could identify the exact application he has.

Tom V.

Seems to be all the time. Smells 'gassy' while driving.

OK stupid question but where is the sight plug on this one? I see pressed in plugs is all it looks like to me... Also looks like there is only one metering block on this carb, and two idle adjustment screws, one on each side correct? Idle screw is to the right of the red spring wrapped adjustment screw at the front of the carb if I am getting this right. Close-up picture attached.

I read 14 inches of vacuum at idle when warm. Adjusting for my 4000ft elevation, that's 18 inches equivalent at sea level. The car definitely smells "gassy" all the time.

Thanks for the info - explained nicely.

Only numbers I see on the air horn, front of carb, read: 80555-1, and below that is 0327 (date code I assume).

Another Wrinkle....
 

So I got out ye olde trusty timing light - an older model Craftsman with a dial advance knob - to see what the timing looks like.

YIKES. I'm not sure how this this is running - timing is waaaayyy retarded. Else the balancer is on wrong but I don't think it's possible to do that...? It has to be 25 degrees after TDC or more.

Yes I tweaked the advance knob and it moves the mark as it should.

So what should my idle advance be - 8 degrees BTDC?

I am surprised it was even able to idle steady even when fully warmed up with that timing setting, or that it was not back firing when you hit the throttle!!

I would go for 10 degrees, and then run some 89 rated fuel and listen for part throttle ping or full throttle knock, also check the plugs after some full throttle loading and 4500 shift point for signs of detonation.

If that all goes well then hook the vacuum advance up ,check and note that it's working and note how much timing it's adding and drive the car and listen for part throttle pinging taking place.

It helps to have someone drive next to you to listen.

You probably don't want to see more then 10 degrees of vacuum advance showing up if the motor as a factory Cam, so you may need to exchange that factory one for a aftermarket adjustable one.

If all is happy on 89 octane fuel then run 91 all the time just to be on we'll safe side of things with the factory cast Pistons.

You will drop off maybe 2 hp with the extra octane but be safe and happy!

Initial timing is no way to set an 55 year old engine;

Try for 32-34* total ADV (vac ADV hose off), at ~2600 rpm, and a Q-JET to see if the problem goes away.

Did you disconnect the vacuum advance before checking (#1 front driver side)?

I did a bit of research and the version you have does not have externally adjustable floats. There are no sight plugs on that series. You would have to remove the float bowls to adjust on that series car. Adjustment is done by just bending the float arm to make the float parallel to the bowl. It is non-critical and would have to be off by a mile and flowing out the breather tubes to have much of an effect.

It may also have power valve blowout protection if yours is an 80555C. They do mention a 6.5 Power Valve which differs from the current spreadbore spec of 8.5. There should be no issue there and you would literally have raw fuel dripping from the exhaust and a cloud of smoke on startup if the power valve failed. I cannot say for certain which power valve (vacuum range) you have in yours as an 8.5 and a 6.5 were used on different series carbs.

I would say that your choke just stays on a bit too long on cold startup and you are seeing some soot from an over-richened choke or a choke unloader that doesn't pop the choke plate back open far enough on cold start. Both are simple adjustments one would make on any aftermarket universal carburetor.

Here's a link to everything you need to know to have that Holley running as it should. It may already be aside from a rich cold start condition. There are a lot of Qjet fans here but I'm not in that camp.

https://documents.holley.com/199r10012-1rev1.pdf

Spreadbore Carb 8055-1 is typically marked only with 5 numbers:
The "List Number" in this case 8055 and the revision number -1 for your carb.
The Carb # is for a 1971-1972 Chevy engine.

There is also a carb with the number 8051-1 that is also for a Chevy.

Look at your numbers again. You have one too many numbers. 8051 or 8055?

Tom V.

https://i.ebayimg.com/images/g/3OAAA...Zt/s-l1600.jpg

Vacuum secondary spread-bores used a 6.5 Power Valve so yours has the 6.5 and does not need changing unless leaking due to backfire damage. Again, it would run so poorly it would be obvious.

The double pumper used an 8.5 Primary power valve and 6.5 secondary which is where I got that 8.5 number from.

I really appreciate the help on this. This forum is such a great resource - thanks to people like you willing to lend a hand. :)

My Holley Book for list numbers is obviously out of date for a carb with that high of number.
So the carb, even though it is a spread bore, was built MUCH later than I assumed.

Sorry for the confusion.

The web posts say that some are not happy with that carb. 2 stars out of 5 should tell you something.

Tom V.

I was able to increase the vacuum from 14 to 16 inches by adjusting the idle mixture screws. Still getting a heavy gasoline smell out of the exhaust.

I have not been able to figure out what the heck is going on with engine timing, however. I have the vacuum advance disconnected and have capped the port on the carb that it connects to. Measuring manifold vacuum from the intake manifold fitting.

I have turned the distributor as much as I dare (at this point) to advance the timing, but the timing is still way beyond TDC. The idle speed did not change much as I advanced the timing, and that has me curious.

I have never seen timing so far out of adjustment and am afraid I'm missing something critical here. Yes I verified I'm on plug #1. There is only one scribe mark on the harmonic balancer.

Any ideas?

Is the mechcanical advance in the distributor brining in more timing with the rev’s above 1500?

If you look down into each primary throttle bore with the motor at idle do you see fuel dribbling out of the booster?

I can't explain the timing but it shouldn't even be able to run at 25 ATDC.

exactly my thinking... something's off

Yes I can see the mechanical advance working.

No.

I note that since I've advanced the timing from where it was, it runs rougher but has more overall power. No sign of pinging.

Thinking maybe my timing light is acting up?

Check your harmonic balancer, too. The ring could have moved.
 

It was mentioned once, but you need to confirm that the timing mark is indeed at TDC for cylinder #1. If the mark is off, everything else is moot.

Have you tried to just turn the distributor until the timing is actually at 8* BTDC with the vacuum advance disconnected and plugged?

You will probably need to turn your idle speed down if you do this, and then readjust the idle mixtures, too.

Just curious.....

Spent some time checking to make sure the distributor rotor was in fact on #1 plug wire at TDC. Was thinking maybe the PO had everything rotated one position. All looked good however.

I did turn the distributor more and got the timing close to TDC, but the idle actually decreased rather than increased as I would have expected. Idle is noticeably rougher and car just runs like crap.

Will readjust idle mixture and see what I get.

Verifying the mark on the balancer is correct is a little more complicated.
 

You will need a helper to do this.

Remove the spark plug from cylinder #1.

Put a big socket and breaker bar (or a really long ratchet) on the crankshaft/balancer retaining bolt.

Turn the crankshaft clockwise (when viewed from the front) until the timing mark on the balancer starts coming up from below the timing marks/numbers on the timing cover. Try to stop at about 5 or 6 o'clock.

Have your helper hold his/her finger pretty firmly over the spark plug hole for #1. They will feel either suction or pressure at different points as you rotate the crankshaft. That's normal.

Keep rotating the crankshaft clockwise.

As the timing mark on the balancer rotates up, your helper should feel pressure pushing his/her finger off the spark plug hole if the cylinder is on the compression stroke.

There is a 50/50 chance this will happen the first time you come up on the marks. If there is no pressure, cylinder #1 is on the exhaust stroke. Rotate the crankshaft one complete rotation and do it again.

If you visualize the harmonic balancer as a clock, with the timing marks at about 10 o'clock, the pressure should start at around 5 o'clock as you rotate the crankshaft.

You may have to repeat this a couple times to make sure you're on the compression stroke.

When you are on the compression stroke for #1, the pressure should build up just until you get to the 0* timing mark on the timing cover. As you pass 0*, the pressure should change to suction and pull your helper's finger against the hole.

This does not mean that the pressure instantly changes to suction. Work the crankshaft up to the 0* mark and pause until the pressure bleeds off. Then keep turning the crankshaft clockwise and see if any more pressure builds up.

If the pressure continues to build after you pass the 0* mark and then starts sucking in approximately the area where you are now seeing the timing mark when the engine is running, the harmonic balancer is bad and the outer ring has slipped.

Hopefully my explanation is not too confusing......

If you're not sure your timing light is functioning right, you may want to borrow a known good light and verify. Or put your light on a known, correctly timed engine and see what is indicated.

Good luck!

Having the Rotor point at TDC when on the timing mark many times means you are probably one tooth off on the distributor installation. It has to be pointed before the
the #1 terminal and you need to know that a Pontiac distributor rotor moves counter clockwise. But you probably already know all that.

Tom V.

Question for the OP here.
Your rotating the distributor and having it run ruff and have the rpm drop is a sure fire sign that your turning the thing the wrong way!

The rotor in these motors spin counter clockwise, so to advance the timing you need to spin the distributor towards the driver side of the car.

If your going things right you should be able to rotate it far enough that the starter will not be able to crank the motor over.

Thanks. Am familiar with this and similar procedures. I plan to pull the valve cover and verify compression stroke.

Agreed - thanks.

I can observe the timing mark coming back towards TDC so I know it's going in the right direction. I am turning the distributor clockwise as viewed from the top. Am dealing with lousy carburetor tune at the same time.

Well No Wonder.....
 

So I guess I should trust my instincts more. Turns out the PO had intentionally retarded the timing in order to get it to run halfway decent with a bad carburetor.

Took the car in to a local mechanic and he discovered that the idle mixture screw for the left bank is broken / has no effect. He also verified the crazy timing setting and set it back to 8 BTDC as it should be. Car now really runs like crap.

Off to buy a replacement carburetor. Many thanks to all who have helped me work through this.

Factory intake doesn't have a "left bank" mixture screw.

Did the mechanic say anything about the metal covering the EGR ports? The way the mixture screws work on that carb, a bad vacuum leak would make a screw non-functional.

Did the mechanic verify TDC on the balancer.

Did the mechanic blow out or clean air bleed holes to try and get that mixture screw to work?

Slowing initial timming for a bad carb makes no sense at all. That would just make things worse.

Need to verify the TDC mark and then, if needed, pull a valve cover and check "cam timing". It can be looked at on cylinder 1 or 6 during overlap. We can get you plenty of directions on here for that.

Clay

I missed this......
 

Posted by QUICK SILVER
Did the mechanic say anything about the metal covering the EGR ports? The way the mixture screws work on that carb, a bad vacuum leak would make a screw non-functional.

I never paid that close of attention to the pic and didn't notice that piece of metal..........it looks pretty primitive and I don't know how it would ever seal the passages correctly.

Here's a suggestion that won't cost too much:

Pull off the carb. Tape off the intake openings with blue tape.

Remove that piece of metal covering the EGR ports. I can't even guess at how it is secured.....

Either get a REAL EGR block-off plate and gasket from Edelbrock (or someone like that). Even better, put expansion plugs into the two holes under the metal piece. You should be able to measure them approximately and then go buy $20 worth of plugs at NAPA or somewhere similar. Use the two that fit and take the others back.

Remove the blue tape, reinstall the carb and see how it runs.

I wish you were closer to Vega$ - we've got a half-dozen known good carbs (Holleys, AFBs and quadrajets) just for situations like this. We'd swap one on and see how it runs. Usually take about forty-five minutes to diagnose and pinpoint the problem.

Good luck!

Guess I could have worded that much better. Meant driver side idle adjustment screw had no effect.

I had no clue (obviously) about the EGR ports having been blocked off, but it makes sense because this engine was a transplant from an early 70's car.

So it looks like I'll spend my saturday verifying TDC and pulling a carb. :(

While you’re confirming TDC also check how much slack is in the timing chain!

I'm thinking botched install of a multi keyway timing set.

Would almost bet on it if the TDC mark checks out good.

That would explain the running better with initial timing way off.


It wouldn't be the first
Clay

Honestly, that soot is just a car warming up with the choke on. It's a nothing.

Forget the timing light you have since you are just getting erroneous readings anyway and have no measure of where TDC is to calibrate from.

Here is a simple method to get you in the ballpark. Attach you vacuum gauge to full manifold vacuum. Start the car and when warmed up, adjust your throttle to a comfortable high idle. Loosen you distributor and rotate it to the highest vacuum reading at idle. Back off an inch of vac by rotating the distributor counterclockwise from the highest vacuum setting. Lock the distributor down, readjust your curb idle speed and drive the car listening for any rattling (pinging) at light throttle under load and note if hot cranking with starter is slow (caused by too much advance and resulting pre-ignition kick-back). Both indicate too much advance. If so, retard the timing by slight counterclockwise rotation to another inch less vacuum. Drive and check, repeat until until you have no ping or hard start.

Then move on to your carburetor. With the throttle closed (no throttle input) look own the primary throttle bores at the transfer slots (a single groove that run down the side of each bore/venturi. The top pf the throttle blades should be just slightly lower than top of that slot (carries idle bypass air around the throttle plates to the engine at idle) If the length of the slot above the plates is longer than it is wide, adjust your idle speed screw until the slot appears as a square. This is called "squaring up the transfer slots".

If the transfer slots are already "squared off" at idle, then your problem lies elsewhere, but I'd be willing to bet you will find too much transfer slot exposed in your current condition.

If you were to start the car, in all likelihood it would idle too slow to run as you do not have sufficient idle air bypassing the throttle blades. However, if you raise the idle by the screw, you uncover more of the slot and create a vacuum signal that induces an over-rich condition. This is where you take the carb off, flip it over and add idle air through the secondary idle speed screw concealed under the carb (to keep the "kids" from tampering with it). The easiest way and best place to start is to loosen or tighten the screw until you can slip a .015" inch feeler gauge between the throttle plate and the secondary venturi wall.

Reinstall the carb, start it up, adjust the curb idle speed to normal and then adjust your mixture with the vacuum gauge.

If you find you have to add excessive turns to the curb idle speed screw to get it to idle, you may have to repeat using a, .020" feeler gauge and reinstall but typical that .015" setting will get it right and only a slight curb idle speed adjustment will be needed.

I was able to compare my timing light against another and it's fine. Still the question about TDC....

I spent some time adjusting the idle mixture screws today, taking my time and watching the vacuum gauge. Not sure what that 'mechanic' did but I was able to get the thing to stall when the mixture screw was run in all the way. He had told me it had no effect. So much for that guy.....

Anyway, I was able to make a slight improvement but the thing still runs like crap - misses, smells gassy, etc. Nearly impossible to drive at a steady speed without bucking along. Accelerates OK but still crappy overall. No pinging heard at any throttle.

Interesting that during the adjustments I increased the idle speed screw setting to keep it from dying so quickly, then tried to reduce the idle speed to near stall, but it NEVER got to that point even after the screw was backed off all the way.



This makes sense - I'll take a look.

Thanks for the input!

Did the car run that way when you bought it? Have you replaced the distributor cap and rotor or plug wires? Don't overlook the obvious, check the firing order. I am sure everyone has done that once in their life.

You need to baseline the car or take it to a mechanic that knows how. The firing order needs verification, as does the distributor installation. The timing needs to be set and the curve checked. And on and on. Very basic stuff.

This needs to be double checked.

After reading your comments on the timing, and the fact that the engine runs so poorly if you try to adjust the timing to the proper 12* mark, I would place my money on the timing chain being installed improperly. Timing chain sets with the multiple keyways on the crank gear are sometimes installed incorrectly resulting in the camshaft being retarded. I've ran across this several times over the years when troubleshooting customer's cars. The symptoms have been the same as yours. The engine runs poorly and won't idle when the timing is set to normal specs. And the engine has poor power when it does run.

I did verify the firing order already. Will need to spend some time verifying timing, etc. I have found a rebuilt quadrajet for a good price and will pull the trigger on that this week. Next week is toast but when I get back will dive in.

Many thanks for all the input / tips / suggestions!