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