My 63 is misbehaving.

[David Thomas]

I hope someone can shed a little light on this, cause' I think it's dark up here right now.

 

My 63 runs great, idles fine, vacuum gauge is steady when using ONLY the primary side of the Carter AFB. If I crack the secondaries, it starts stumbling shaking missing, will not rev any more and will occasionally backfire, of course vacuum goes virtually to 0 when the secondaries are opened but bounces right back. I can rev it all day on the primaries and it will run without missing a beat, pulls strong. It will cruise at 60 - 80 mph as long as it is on the primary butterflies. As soon as I crack the secondaries it will start to stutter. I can rev it in neutral and get the same results, so it does not have to be under a load to misbehave. Vacuum stays steady when holding a high idle.

 

Here is what I've done so far, by steps.

 

1. Check timing, balance carburetor. Noticed dwell would vary from 33° at idle down to about 28° with increased rpm.

2. Rebuild carburetor, found nothing wrong. I really thought the secondary circuit was plugged up because I very seldom open them.

3. New rotor, Dist. Cap. Old were sort of iffy

4. Check plug wires with Ohm meter, looked normal

5. Check voltage to coil and Pertronix trigger, cleaned all connectors. Voltage was good, 14 + volts to coil and ignition module.

6. New spark plugs and wires, old looked ok.

7. New fuel pump, blew compressed air through line back to tank.

8. Checked Flame Thrower coil, 1.8 ohms across terminals, 8K ohms from terminal to tower.

 

 

Unless the ignition module is breaking down or the coil is weak, I'm at a loss. I would think, if the coil or electronic trigger were failing it would run poorly on the primary circuit of the carburetor, also. I'm stumped at the moment. The variation of the dwell is not out of line but may be an indicator the module is suspect. I would think, it should hold steady.

 

Thanks.

[Jason Edge]

David is correct about vacuum going to zero under sudden WOT. The engine creates vacuum with resistance to air fuel mixture, especially at idle and low rpm, but when you suddenly open the butterflies up wide open it removes that air fuel resistance and intake vacuum decreases.  This is the main reason you have a distributor vacuum advance to advance spark timing at idle and low rpm and use centrifugal weights and take advantage of inertia to advance time under very high rpm situations. 

[David Thomas]

Hi Tony,

The plugs are dark gray to brown, to me that indicates a slightly rich mixture. If they were a light gray or white gray to brown I would think a leaner mix. Those plug readings were with the old plugs, before I put a kit in the carburetor.

Float level and drop are correct. I thought at first the secondary circuit may have been restricted with gum because it is seldom I open them. Plus, the car will frequently sit for weeks which allows fuel to evaporate, possibly leaving behind deposits. It has been 40 or 50K miles since I last rebuilt the carburetor, thinking enough evaporative cycles have occurred over the years to leave sufficient deposits to form. Unfortunately, that was not the case, when I opened the carburetor it was very clean inside with very little sediment in the bottom of the bowls. I started to remove the sediment, button it back up and re-install it but decided to put a kit in it because it was off the car. As stated in my original post, the carburetor is the Carter AFB. The puzzling thing is, the poor running immediately starts with the opening of the secondary butterflies. I have verified by watching, the secondary circuit in the carburetor flows fuel through the venturi nozzles when the secondary butterflies are opened.

Yes, I have rebuilt this particular carburetor about 3 times through the years and lots of Rochester's, Quadrajets, 4G's and single barrel, along with many Autolite and Holly carburetors. Not my first time to work on a carburetor.

Any time you rapidly fully open the throttle on any engine or carburetor style, the vacuum will momentarily go to almost 0". The reason being, you have removed almost all the restriction in the intake with the exception of the restriction the venturi area of the carburetor produces. As the engine rpm increases and the CFM of intake increases, the venturi of the open carburetor will play a more restrictive roll causing the vacuum to increase. Try it on your car, hook up a vacuum gauge and let the engine warm up, then slam the throttle wide open from idle while watching the gauge. The vacuum will immediately drop to almost 0", when you release the throttle the vacuum will immediately increase to 20" or more, until the rpm reduces to idle again and the vacuum stabilizes.

I did correspond with Pertronix relating the variation in dwell. They sent a PDF file with instructions on diagnosing the coil and ignitor. Unfortunately, they did not acknowledge the dwell and in the tests there is no mention of dwell.

Thanks for your thoughts,

David

Text from Petronix test procedure;

Grounds

It is imperative that the power and grounds be checked as part of the installation procedure. After

installing the kit within the distributor and with the distributor in the engine, using a digital multi-meter

measure the resistance from the aluminum plate holding the module to battery (-) terminal. The net

resistance must be less than 0.2 ohms. The net resistance is the meter reading minus the resistance of

the meter leads. If the net resistance is greater than 0.2 ohms the source of the faulty ground must be

found and fixed. Usually the source of the bad ground is easily found by holding one probe on an original

location and moving the second probe toward the static probe. Where the resistance drops identifies the

source.

Maximum Resistance from Ignitor plate to Battery (-) Terminal.

0.2 ohms

EXAMPLE:

Resistance from Ignitor Plate to Battery (-) Terminal. 0.4 ohms

Resistance of meter leads.

(-) 0.2 ohms

After subtracting meter lead resistance, your total resistance is:

(=) 0.2 ohms

•

Ignitor “MUST” be grounded properly to the distributor housing.

•

Distributor Housing needs to be grounded PROPERLY to the engine or intake.

•

Check contact surface area of distributor “Hold down Bracket” for proper ground.

Coil resistance and Specifications

ENGINE Resistance Specifications Recommended Pertronix Flamethrower

coils

Cylinders Minimum Maximum Black Chrome Epoxy Ind/Ag

1, 2, & 3   3.0 ohms 4.5 ohms 40511 40501 40611 28010

4 & 6         3.0 ohms 4.5 ohms 40511 40501 40611 28010

8 & 12       1.5 ohms 4.5 ohms 40011 40001 40111 N/A

Note: Installation of the Pertronix coil is not required. Insure that coil being used has the

proper resistance or install an external ballast resistor to increase the resistance to the

minimum required.

Measuring Coil Resistance

1. Remove all wires from the coil, including Ignitor and your harness wires.

2. Using a digital Ohmmeter, connect one lead to the positive (+) terminal of the coil and the other

lead to the negative (-) terminal of the coil.

3. Note ohmmeter reading, insure ohmmeter reading is within our specifications or install an

external ballast resistor if the reading is too low.

4. If the ohmmeter reading is above the maximum specified, replace coil.

Voltage Test

1. Place ignition switch in the off position.

2. Do not disconnect wires from ignition coil.

3. Use jumper wire (With alligator clips on both ends)

4. Connect jumper wire from negative (-) terminal of coil to a good engine ground (

See

Figure 2).

5. Connect voltmeter red lead to positive (+) terminal of coil and black lead to engine

ground (

See Figure 2).

6. Turn “ON” the ignition switch and note voltage reading. Quickly read voltage and turn

ignition “off”. See chart below for specifications.

7. Remove jumper wire or engine will not start.

                                                            Minimum Normal Maximum

Ignition Switch “ON”, Engine “off”           8.0V     11.5V     N/A

Engine Cranking                                     8.0V     9.6V or Greater N/A

Engine Running N/A                               14.2V    16.0V

Note: When resistors are NOT present, you should have a normal voltage reading or close to

it. Low voltage can be caused by poor connections, poor contacts in the ignition switch, ballast

resistor, and or a resistance wire in the wiring harness (Factory Installed).

[David Thomas]

Hi Russ, yes, the timing is steady, 5°, and the advance is still installed and working. Engine runs smooth and pulls good, until I open the secondaries.

Tony, I should have stated the vacuum drops to 0 when the throttle is quickly opened wide, then rises as engine rpm increases or the throttle is closed.

Thanks.

[David Thomas]

 

Tony, Jk, thanks for your thoughts.

Answers to questions below.

Tony,JK,  The old plugs were a brownish gray color, had about 15K on them. I have the Pertronix I and matching Flamethrower coil, been installed since 2004. The vacuum advance is operating properly. Timing is steady and the mechanical and vacuum advance work fine. I don't have any way to check the coil or ignition module other than replace them. The varying dwell does raise a flag to me, I don't remember points ever doing that, I think they held a steady 30°. The distributor is in good condition, no slop in the shaft or point plate. The Carb gaskets are new and in proper sequence with the stainless shim under the carb. I watched the carb throat while opening the throttle, getting a good stream of fuel through all 4 venturi when all 4 barrels are open. With the engine running, I checked ground to the point plate back to the battery terminal, 20mV, virtually a perfect ground. I did all the work, including the carb rebuild.

I shot off a message to Pertronix customer service with an inquiry, hope to hear from them soon.

Thanks

David

 

.

 

[David Thomas]

Since I've changed just about everything fuel related, at Jason's suggestion, I replaced the fuel filter. Unfortunately, that didn't help. The old filter did have a fine red coating on the paper, so, it didn't hurt to change it.

[David Thomas]

Jason,

It has run out clean at full throttle not too many months back. The only thing that changed, was time and miles.

I have not changed the fuel filter lately. Looking through the glass at it, there is very little debris collected, it looks ok, but to be honest, I haven't pulled it out. Maybe today's E10 fuel has damaged the old AC filter material. I have some more AC fuel filters, would not hurt to give it a try. I did put a new screen in the carburetor inlet when I put the kit in it. All the passages in the carburetor are clear. It does seem like a lean condition when the secondary circuit comes into play.

[Jason Edge]

2 questions: 

- Has it ever run correctly on hard throttle & using the secondaries?
- If Yes, has anything been changed between running right and not running right?

It tends to make you think something is not just right with the carb even though  you said it has been rebuilt.  I would also ask if the fuel filter is nice and clear and not clogged, also the screen on the carb inlet where fuel line attaches. When you kick in the secondaries it needs much more fuel delivery. I remember on the cherry red sedan deville I had years back the fuel filter was clogging up and I was about 30 to 40 miles from home and had to end up driving it about 10 mph less than the speed limit as it really started to sputter at 65mph..and I'm guessing that was just on the primaries.