Carter AFB about to become a door stop...

I have a 65 Buick wildcat with a nailhead 401 and TH400. The carb ran like crap when I got the car so I did a weekend rebuild in my garage that didn't make any difference.

I took it down to the local white hair who has done good work for me before and definitely knows his stuff (he knew the carb was for a mid 60's Buick while I was still holding it and walking through the front door of his shop. He worked on it for a week and did a tune once I got it on the car. Things Improved but not enough.

Here's the symptoms:

Choke works well and car starts even when cold.

The engine is running rich enough to leave a black spot on my driveway under the tailpipe.

I have leaned out the idle mixture screws as far as they will go before the RPMs drop

Vacuum hoses are in good condition and are routed just like they were from the factory.

Not sure if any more information is necessary but I can answer specific questions.

Any ideas?

 

No ideas other than to junk it. I had a 600cfm Carter on my Edsel when I first bought it. Tried everything, rebuild, every mixture, different fuel pressures, nothing. I bought a used Edelbrock 1406 and slapped it right on with no issues whatsoever. It was cheaper than rebuilding my Carter twice.

 

Go too Sears and buy vacuum gauge... They have those at the tool dept. Next lightly turn the mixture screws in till they seat then back them out one full turn.. Start your engine up and let it idle till it warms up.. Next hook the vacuum gauge up to a vacuum source on the intake manifold and slowly re-adjust the idle mixture screws on the carb till you get the highest reading on the gauge... As your doing this, you'll notice the engine start to smooth out... Let us know how it turns out!!!

 

I use a vacuum gauge all the time when I tune a carb, hands down the best tool for the job, unless something is blocked within the carb or something else is effed up with it.

Bob

 

What fuel pressure do you have?

 

While there are certainly other possibilities, the two major contributors to an engine running this rich are:


(A) defective carburetor
(B) defective ignition system

Carter Carburetor Company in St. Louis had 1000 cars with "carburetor trouble" as diagnosed by "professional" mechanics sent to them.


The actual causes were:


(A) poor compression - 2 percent
(B) defective ignition system - 93 percent
(C) defective carburetor - 5 percent


And this from a company that made their profits selling replacement carburetors and rebuilding kits.


Jon.

 

>>>>>>>x2<<<<<<<

 

The idle screw adjustment is fine, but will only affect the engine's running quality at idle. If you're having problems at speed, maybe you should get a kit and experiment with changing the metering rods and / or jets. If you want the optimum, take it to a shop that can weld bungs on the exhaust pipe(s), hook up an O2 sensor and have them tune it for you.

Bottom line is, there's a lot of adjustments and fine tuning available with any carb. You shouldn't expect to buy a carb, bolt it in and have it run perfectly with your particular engine - way too many variables.

 

I just went through this with my Caddy I just sold...bad ignition coil!

 

The Edelbrock carbs ARE Carter carbs, made by Weber.

 

It probably couldn't be this simple but is the engine making enough vacuum for the enrichment circuit to work properly? Maybe 15" or more at idle, no load?

Are the power pistons moving freely in their bores?

Are the tips of the metering rods bent from them being "clumsily" installed?

Sunk float or debris in the needle and seat?

X2 on the vacuum gauge. Great for diagnosis, then install it in the car so you can monitor it while driving.

 

That must be where that saying comes from.
"90% of carburetor problems are electrical in nature "

 

You do know what AFB stands for!! Always Fucking Broke!!!

 

Thanks for the great input. I have never used a vacuum gauge but Ive heard that tuning with a tach isn't too far off.

The fuel pump is stock so I'm not too concerned with the fuel pressure.

I went through the ignition system when I got the car (because it was the only thing in worse shape then the carb.) which included plugs, points and timing. After Three days of chasing gremlins I discovered the plug wires were in the wrong order!!! It was amazing that I was able to drive the hour from the sellers house. The only thing I didn't touch was the giant ugly yellow Accel coil. I'm thinking that I should have.

Looks like I'm adding a vacuum gauge and a stock coil to my shopping list.

Any other ideas?

 

Yea get a compression tester with your vacuum gauge.
Search the techs for vacuum gauge tuning and diagnosis,
that Trans should be the ST400 unless it was changed to a TH400.
Your gonna love it when you get it dialed in.

I most certainly would check the fuel pressure if you are suspecting Carb trouble on a rebuilt x2 Carb. Just saying

 

So, what's the real problem?
You haven't really said what's really wrong with it yet other than "it runs crap".

Does run 'crap' while idling, driving or accelerating?
How much voltage at the coil at idle?

 

That's what I thought until I checked fuel pressure on a stock Chevy pump,9 psi!

 

X2. Had similar issues with a Holley and a stock parts-store fuel pump. Put a pressure regulator on it...problem solved.

 

I wouldn't worry about the coil. There is no such a thing as too hot an ignition and coils either work or they don't. if it isn't working you will be the first to know.

I am probably way off base on this one but I might suspect that you could be pulling fuel from your secondaries. You may want to make sure that your secondary butter flys are closing properly.

Just a thought and something to help muddy up the waters.

 

The Edelbrock may look like a direct replacement, but be ready to muck about with the kickdown brackets.

 

Just a shot here but i have seen some with the wrong temp plugs foul out quickly and run like crap.

 

Yeah, a tach is handy too. But about 90% of the adjustments and transitions that a carb has to make to work properly under different driving conditions are determined by manifold vacuum and air flow, not directly by engine RPM.

 

Problem is only apparent at idle. Otherwise it has good throttle response and decent power throughout the rpm range.

 

Did it have brass floats? I had issues with an old Rochester carb I used, and it was taking on fuel, as the float was sinking slowly. It would load up at idle, but run okay once off idle.

 

I don't usually disagree with the 'Beaner, but this time he's dead wrong. Coils can and do get progressively weak, weak enough to appear as a overrich fuel mixture. And you'll be the LAST to know, as someone else will say "is the coil good?"

Change the coil, it WILL help.

Cosmo

 

Some of the Buick AFB carbs have the two idle mixture screws, plus the curb idle screw on the side; others have the two idle mixture screws and an idle air screw between them. Which do you have?

Generally, these things tend to run too LEAN at idle with the modern fuel.

If you have the idle air screw, suggested initial setting is 1 turn on each mixture screw and 1 1/2 turns on the idle air screw.

If you don't have the idle air screw, suggested initial setting is about 1 1/4 turns on the idle mixture screws, and set the RPM with the curb idle screw.

In any event, these adjustments should be made when the engine is at full operating temperature.

One further question: If you start and drive the car for 15~20 minutes, THEN return to the driveway, do you get the black spot; or only on initial starts?

I would still check the compression and ignition first.

Try to find an oldtimer that has an oscilloscope with which you can measure firing voltages at the individual plugs.

Jon.

 

Is there a way to test a coil?

 

Sun machine is the only positive way I know.

Cosmo

 

All my cars with exhausttips turned down on the end leave black spots. But only during warmup. I say the problem is the way the exhaust ends

As for testing a coil, you can put a sparkplug in the main cable and hold it 'near' grounded metal on your car. Have someone crank over the engine and slowly move the sparkplug away from the metal. The longer the arc, the better the coil.
I think you should be able to draw at least 1 inch long arcs.
Coils can get weak or cutout when they get too hot. Either by too much voltage on the primary side or when it's mounted in a hot location.

 

If your nailhead is like the one in my 65 Skylark GS it should have a seperator plate between the manifold and carb. If the plate is missing or deteriorated it will cause massive vacuum issues at idle and your mixture screws will do nothing. This plate blocks the heat riser passage in the manifold from mixing with the fuel/air circuits of the carb. I bought and installed a very good rebuild on my carb and it still ran like crap at idle...bought a new plate and it fixed my idle mixture problem.

http://www.oldbuickparts.com/catalog/product_info.php?cPath=38_50&products_id=2673

This is the one I bought.

BPD