Any idea on this misfiring mystery?

[Hans R.]

I got misfiring problems in my 1966 327 300hp car. In order to locate which cylinder have the misfiring issue, I disconnected each ignition cable at the distributor cap. When I pulled the cable for cylinders 1, 4, 6 and 7 it effected the engine idle. When I pulled the cable for cylinder 8, 3, 5, and 2, it had no effect on the idle even though I could see a spark when moving the cable close to its position in the cap. According to the firing order, this means that every other cylinder have a misfiring problem.
Does anyone have a clue on what could cause this misfiring pattern?

Thanks for any idea!

[Bruce B.]

Re: Any idea on this misfiring mystery?

Look at the post Ignition Problem, it is on a C1.
Another strange situation.

It was posted a little earlier then your post.

[Mark E.]

Re: Any idea on this misfiring mystery?

Hans,

How would you describe the "misfiring problems" you're having? Details about when it occurs (all the time, varies with engine speed, car speed, load, etc.) and what it does when misfiring would help.

Is it possible you need an old fashioned tune up? Fouled plugs or weak cables could explain your symptom. But without more information, the problems may be elsewhere.

[Bill L.]

Re: Any idea on this misfiring mystery?

Hans:

Mark came up with the best idea --- "Good Old Fashioned Tune-up"!!!

I would state the obvious here:

Points (and gap adjustment)
Plugs (and gap adjustment---are any of them fouled???)
Rotor (make sure you have the correct one --- i.e. long enough to make contact -- not an aftermarket one that is too short)
Distributor Cap (internal contacts [they get messed up over time] and check for a cracked plastic body as well)
Plug Wires (carbon vs. wire --- several posts on this subject on the forum)

Others will amplify on this --- just don't assume "ONE THING" is the culprit --- it may be but while you have the hood up check everything else as well ---

{I am a firm believer that these old cars sit in our garages and just think up ways to vex us -- especially when we don't drive them or pay attention to them on a regular basis -----)

Hope this helps...

Regards
Bill

[Wayne W.]

Re: Any idea on this misfiring mystery?

2-3, 5-8 are on the same plane in the manifold. Any strong vacuum leak can cause that symptom. A 5-8 miss is very common because most vacuum devises are attached on that runner, but could affect 2-3 also. A carb that has a problem on one side is also a possibility.

[Edward J.]

Re: Any idea on this misfiring mystery?

Hans, does the car get driven much, have you had a trip that is long enough to bring it up to temp lately? sometimes we tend to start up cars and not run long enough to burn the excess fuel of the tips of the plugs, and fouling will occur very quickly. and sometimes a good hot run down the hwy can burn the excess fuel from the tips of the plugs. If not try a set of plugs first would be my first step .If the car had no running issues prior its likely fouled plugs, also ,make sure the choke is working properly and not staying closed for to long.

[Duke W.]

Re: Any idea on this misfiring mystery?

Odd problem, but one thing to definitely check is that the #1 wire is in the proper dist. cap terminal, and the remaining wires proceed clockwise in the firing order. The CSM should have a diagram. It's easy to get the wires mixed up, so check each wire with an ohmmeter end to end, which will also tell you if any wires have excessive resistance. More than about 5K ohms per foot indicates a need to replace the wire.

Duke

[John O.]

Re: Any idea on this misfiring mystery?

Hans,
I had the exact same problem with my 64 250HP roadster. It turned out to be one side of my carb (WCFB) was not functioning properly. I rebuilt it and everything works fine now. Apparently, the cloth part of the seal on the accelerator pump came apart because I had parts of it in the primary bowl, and some must have stopped up the main jet on one side. You might get it running by taking the top off the wfb, cleaning the bowl out and replacing the accelerator pump, assuming its bad, with a new one that's ethanol safe.
Steve

[John O.]

Re: Any idea on this misfiring mystery?

Hans,
Just to be clear. I went through all the ignition stuff, changed plugs, changed coil, changed points and condenser, nothing worked. Then I started pulling the plug wires at the distributor just as you did. Every other one had no effect on the idle. With our dual plane manifolds, half the carb feeds half the cylinders. Look at your manifold. Half the runners are high and half are low. The low runners feed cylinders 1,4,6, and 7, ie every other one in the firing order. The high runners feed 8,3,5, and 2. Your problem is definitely related to fuel delivery, not ignition.
Steve

[Hans R.]

Re: Any idea on this misfiring mystery?

Thanks John (or Steve?) I think you are on the right track. Also thanks to Wayne who also pointed to a carburetor issue. I did not give all the background details up front because I wanted to see if someone could pinpoint the problem just from the strange symptom. And you did! Now that you have explained the pane pattern in the intake manifold it is not so strange anymore. This is the background; It started with a leaking inlet valve on the secondary side of My Holley 4160 3367 carburetor. I replaced that and while at it I also changed it on the primary side. Plus replacing accelerator diaphragm and power valve. I also checked and cleaned the spark plugs, changed ignition timing from 4 t 6 degrees (according to books) and changed the Dwell Angle from 28 to 30. So I touched a few things in the fuel/ignition area and I ended up in this misfiring and ruff idle problem. I have tried to set ignition and Dwell back to previous settings but the did not help. So your idea that it is a carburetor related problem is most probably correct.
I will take the carburetor apart and check carefully if I did something wrong.
Btw, at the moment both idle adjustment needles does not work properly. They have to be adjusted all the way to bottom to get the least ruff idle.
Thanks from Hans Ryden in Stockholm, Sweden

[John O.]

Re: Any idea on this misfiring mystery?

Actually I go by Steve which my middle name. John is my first name and I was assigned that as my user name, probably because I paid with my credit card for my membership. I'm glad to help with your problem. Having every other cylinder misfire is a very unusual set of circumstances, and I started to post on my experience with this problem and how I fixed it a couple months ago, but I never got around to it. Good luck.
Steve

[Timothy B.]

Re: Any idea on this misfiring mystery?

Thanks John (or Steve?) I think you are on the right track. Also thanks to Wayne who also pointed to a carburetor issue. I did not give all the background details up front because I wanted to see if someone could pinpoint the problem just from the strange symptom. And you did! Now that you have explained the pane pattern in the intake manifold it is not so strange anymore. This is the background; It started with a leaking inlet valve on the secondary side of My Holley 4160 3367 carburetor. I replaced that and while at it I also changed it on the primary side. Plus replacing accelerator diaphragm and power valve. I also checked and cleaned the spark plugs, changed ignition timing from 4 t 6 degrees (according to books) and changed the Dwell Angle from 28 to 30. So I touched a few things in the fuel/ignition area and I ended up in this misfiring and ruff idle problem. I have tried to set ignition and Dwell back to previous settings but the did not help. So your idea that it is a carburetor related problem is most probably correct.
I will take the carburetor apart and check carefully if I did something wrong.
Btw, at the moment both idle adjustment needles does not work properly. They have to be adjusted all the way to bottom to get the least ruff idle.
Thanks from Hans Ryden in Stockholm, Sweden

Hans,

Double check that the new gaskets and holes match the old gaskets, these carburetors are modular in design and engine vacuum can find fuel or air internally and pull it into the engine. Make sure the new power valve has the correct gasket and is tight, this can also be a leak path for fuel.

If the side emulsion screws are turned in, fuel available for engine idle is shut off so the engine is finding fuel somewhere else causing issues. If they are turned out, fuel is available for idle but if they are all the way out the engine could be finding air and pulling it in somewhere.

[Hans R.]

Re: Any idea on this misfiring mystery?

I finally got time to work on my problem. I took the carburetor apart, i.e. the primary metering body and the primary fuel bowl.
Everything looked ok except for one thing. When I removed the prime fuel bowl, the Metering body vent buffle was laying at the
bottom of the bowl. I do no know if it came loose while removing the bowl or if it was already loose before I removed the bowl.
I carefully put everything back in place and now the engine runs ok and I'm able to adjust both idle needles to get a smooth idle.
Could it be that the Metering body vent buffle was laying loose in the primary bowl and restricting the right main jet which feeds the
2, 3, 5 and 8 cylinders? These are the cylinders that was misfiring.
If anyone has any idea on this, please share it with me

Thanks to everyone giving their ideas on my problem and leading me in the right direction!

Hans Ryden in Stockholm