Firing un-order?

[Juan Veldez]

Pulled the plugs and noticed that 1,8,4,3 where tan-ish. Plugs 6,5,7,2 were clean as a whistle. Same goes for the exhaust ports and tops of pistons. Thought the carb primary on one side of the dual plane intake was set bad and caused this, but that's not how the ports are separated. Then I realized that this difference is on the 180 degree rotation of the firing order, not the other. Any ideas on what is causing this?

My thought was distributor or distributor cap. The odds of the plugs or plug wires being bad in coincidence with the firing order as noted is astronomical, IMO. The distributor is an original and not updated, yet. The cap, rotor, wires, and plugs were all brand new. New distributor from Summit is on it's way!

 

[Ricks72Chlgr440]

Pulled the plugs and noticed that 1,8,4,3 where tan-ish. Plugs 6,5,7,2 were clean as a whistle. Same goes for the exhaust ports and tops of pistons. Thought the carb primary on one side of the dual plane intake was set bad and caused this, but that's not how the ports are separated. Then I realized that this difference is on the 180 degree rotation of the firing order, not the other. Any ideas on what is causing this?

My thought was distributor or distributor cap. The odds of the plugs or plug wires being bad in coincidence with the firing order as noted is astronomical, IMO. The distributor is an original and not updated, yet. The cap, rotor, wires, and plugs were all brand new. New distributor from Summit is on it's way!

Is this a new engine or one that has been running for awhile?

 

[Juan Veldez]

Is this a new engine or one that has been running for awhile?

Yes, new engine. Just about EVERYTHING is new or at least re-built.

 

[Ricks72Chlgr440]

Yes, new engine. Just about EVERYTHING is new or at least re-built.

The new distributor you have coming will likely fix this. Do you recall if the inside dist cap terminals show anything unusual on any of the cylinders? Just wondering if the shaft bushing has some play or is worn such that when it spins to those cylinders it moves away from the terminals making less spark to them. Just spit ballin'

 

[Juan Veldez]

The new distributor you have coming will likely fix this. Do you recall if the inside dist cap terminals show anything unusual on any of the cylinders? Just wondering if the shaft bushing has some play or is worn such that when it spins to those cylinders it moves away from the terminals making less spark to them. Just spit ballin'

It was a new cap and the terminals looked fine. My conclusion was exactly the same, gotta be spinning away from the magnetic pickup for that 180 degrees of revolution and not sending spark. Thanks for your input, much appreciated.

 

[Challenger RTA]

A picture of the plugs would show the condition better then your explanation. Might be the distributor is wore. just a guess. Was there white corrasion inside the cap? Do you have a tac, was it acting erratic.

 

[Deathproofcuda]

How was the engine running before you pulled the plugs, rough or normal? What kind of vacuum did you have at idle?

 

[Juan Veldez]

How was the engine running before you pulled the plugs, rough or normal? What kind of vacuum did you have at idle?

Seemed to run okay around 2k rpm's at initial start up/break in. Never would idle, so I couldn't get a timing light or vacuum gauge on it, or adjust the carb. Just got the new distributor, so we shall see if that was part of the problem.

 

[Deathproofcuda]

Got it.

I agree with Challenger RTA, would be interesting to see pics of your plugs. How did you inspect the exhaust ports and tops of the pistons?

 

[Juan Veldez]

Got it.

I agree with Challenger RTA, would be interesting to see pics of your plugs. How did you inspect the exhaust ports and tops of the pistons?

I dropped the headers, so I could look at the exhaust ports. Four were charcoal in color in the cylinders noted and the other four were clean as before start up. I could shine a flashlight into the spark plug hole so see the top of the pistons. Here are the plugs and exhaust ports.

 

[Deathproofcuda]

Will be interested to hear your report on how it runs with the new dizzy.

 

[Steve340]

The problem could possibly be something to do with the intake manifold leaking?
Just a thought.
Seems weird it would not idle.
Try the distributor first is a good idea.

 

[Slug]

Were you able to find anything out?

 

[Juan Veldez]

Were you able to find anything out?

Ha, just got it all back together about 5 minutes ago, except I am waiting for two spark plug wires that have 90 degree ends at the spark plugs due to a header tube clearance issue. They arrive tomorrow. I also put on a new harmonic damper. Should be able to start it up tomorrow evening if all goes well - fingers and toes crossed, LOL.

 

[Adam]

Just a thought… Make sure the dist cap is seated correctly. If the drivers side was up, because the pick up wires were pinched under the cap, the rotor would miss 6,5,7,2.

Btw, beautiful engine.

 

[blubyou340]

Pulled the plugs and noticed that 1,8,4,3 where tan-ish. Plugs 6,5,7,2 were clean as a whistle. Same goes for the exhaust ports and tops of pistons. Thought the carb primary on one side of the dual plane intake was set bad and caused this, but that's not how the ports are separated. Then I realized that this difference is on the 180 degree rotation of the firing order, not the other. Any ideas on what is causing this?

My thought was distributor or distributor cap. The odds of the plugs or plug wires being bad in coincidence with the firing order as noted is astronomical, IMO. The distributor is an original and not updated, yet. The cap, rotor, wires, and plugs were all brand new. New distributor from Summit is on it's way!

I have actually the same thing happened a time or adozen rebuilt engines are fun but never like a new crate. My problem on one particular engine 340 was 3 things w hich really messed with my head. The aftermarket distributer cap was slightly shorter and the rotor was firing on the top of the brass contacts then the roller rocker valve lash was to tight for the lifters i reset them all with a quarter turn and the distribuer itself was 008 at the top relucter and inter mittently hitting at the bottom not sure if this will help but worth a try i had 3 plus with just gas and the engine would not idle shook like a top fueller good luck man youll get it after your pissed and leave it alone for a day and google this and that and cuss then a bulb will come on and youll say you dumbass thats what it is !!!maybe not but i do good luck man