65' 396/425 Spark Plugs

[Russell L.]

Does anyone know the correct replacement spark plug for the 65' 396 application? The original AC43N plug is no longer available new, and there seems to be some discussion as to it being too cool anyway.The AC Delco website only goes back to model year 66'. However, it does show the R43XLS as the current replacement plug for the 66' 427 application. I am currently running the R43"XL" not the longer "XLS".

[Dick W.]

Re: 65' 396/425 Spark Plugs

I have had good luck runnin R45XLS's in the 396 cars. Minimal, if any, fouling. Anything colder and you will have problems with fouling.

[Russell L.]

Re: 65' 396/425 Spark Plugs

Thanks Dick, maybe that's exactly what my problem is now. I have had problems with the engine fouling and dying at stops after it is at operating temp. I had carb gone through, replaced fuel filter and coil too. Still fouls and dies at stop when warmed up. Upon cold start it runs great until.... I am running R43XL plugs now and think they are fouled so I will replace them and take the next step toward finding my problem.

[Michael H.]

Re: 65' 396/425 Spark Plugs

Thanks Dick, maybe that's exactly what my problem is now. I have had problems with the engine fouling and dying at stops after it is at operating temp. I had carb gone through, replaced fuel filter and coil too. Still fouls and dies at stop when warmed up. Upon cold start it runs great until.... I am running R43XL plugs now and think they are fouled so I will replace them and take the next step toward finding my problem.

Sounds more like a carburetor problem. If plugs are fouled, they'll misfire cold too. Take a look at a few of the plugs and you'll see if the mixture is right.
Hotter plugs are just a bandaid for some other problem.

[Clem Z.]

Re: 65' 396/425 Spark Plugs

Thanks Dick, maybe that's exactly what my problem is now. I have had problems with the engine fouling and dying at stops after it is at operating temp. I had carb gone through, replaced fuel filter and coil too. Still fouls and dies at stop when warmed up. Upon cold start it runs great until.... I am running R43XL plugs now and think they are fouled so I will replace them and take the next step toward finding my problem.

one of the secrets of keeping the plugs in a street driven BBC is after driving around town take it up in RPMs at part throttle because if you full throttle it cause the temps on the plugs to go up to rapidly and it bakes on the deposits causing fouling. R-45 XLS gap at .035 should work well if all the rest of the engine is in good shape

[Russell L.]

Re: 65' 396/425 Spark Plugs

Good point, by mixture do you mean fuel
/air adjustment?.

[Russell L.]

Re: 65' 396/425 Spark Plugs

The strange thing is the car always ran super well, then I changed the coil,fuel filter and fuel pump. Afterwards the car fouled out at low rpm's, but only after it was at operating temp. When cold, it runs great. I just don't know what's happening here!

[Michael H.]

Re: 65' 396/425 Spark Plugs

one of the secrets of keeping the plugs in a street driven BBC is after driving around town take it up in RPMs at part throttle because if you full throttle it cause the temps on the plugs to go up to rapidly and it bakes on the deposits causing fouling. R-45 XLS gap at .035 should work well if all the rest of the engine is in good shape

Glad you mentioned that Clem. That's EXACTLY what the problem is with using a spark plug that is TOO hot for the application.
Instead of blasting the carbon deposits off in chunks on medium/hard acceleration, it's melted on to the insulator and no amount of cyl pressure/heat will remove it.
That's exactly why spark plug heat ranges are carefully selected by engineering instead of just throwing high heat range plugs in everything.

Always use the coldest heat range spark plug that will survive in the environment it's running in.

And, with todays no lead fuel, spark plug fowling is much less of a problem than it was in the past.
I've had the same set of AC 43N's in my 66 425 HP car for the last two years. I drive it in slow traffic to/from local car cruise-ins and hardly ever get on it. No plug problems.

[Michael H.]

Re: 65' 396/425 Spark Plugs

The strange thing is the car always ran super well, then I changed the coil,fuel filter and fuel pump. Afterwards the car fouled out at low rpm's, but only after it was at operating temp. When cold, it runs great. I just don't know what's happening here!

Russell,

Just curious about the coil. Is it a correct original or reproduction T.I. coil? I learned a long time ago that if something seems to have gone wrong just after someone replaced some part, it's very likely the problem is directly related to that change.
Also, if I remember correctly, the 65 T.I. coil wiring is reversed from all other T.I. systems as the black wire was supposed to be connected to the positive terminal and the white resistance wire was supposed to connect to the negative?? I don't remember if the engine would run at all that way though.

Also, I suppose it's possible that some small particles of dirt were disturbed and wound up in the carburetor during the fuel filter change?

[Joe L.]

Re: 65' 396/425 Spark Plugs

Does anyone know the correct replacement spark plug for the 65' 396 application? The original AC43N plug is no longer available new, and there seems to be some discussion as to it being too cool anyway.The AC Delco website only goes back to model year 66'. However, it does show the R43XLS as the current replacement plug for the 66' 427 application. I am currently running the R43"XL" not the longer "XLS".

Russell-----


If it were me, I'd be using a Champion RN14YC.

[Russell L.]

Re: 65' 396/425 Spark Plugs

Yes, as a matter of fact, I bought an original #210 coil and it tested alright but when I had these problems, I saw it had leaked oil out and was not responding when hot. I replaced it with a reproduction coil. I also found particles of dirt in the rear needle/seat and replaced the fuel filter as well after going through the carb. However, today I started the car and when hot it responded the same as before, fouling out sounding as if it was running on 7 cylinders or out of time. Previously, I had used a NOS fuel filter and I think it passed debris to the carb but replaced it as I have said. Still dies when hot at a stop and misses at low rpm's across the intersection.

[Clem Z.]

Re: 65' 396/425 Spark Plugs

Glad you mentioned that Clem. That's EXACTLY what the problem is with using a spark plug that is TOO hot for the application.
Instead of blasting the carbon deposits off in chunks on medium/hard acceleration, it's melted on to the insulator and no amount of cyl pressure/heat will remove it.
That's exactly why spark plug heat ranges are carefully selected by engineering instead of just throwing high heat range plugs in everything.

Always use the coldest heat range spark plug that will survive in the environment it's running in.

And, with todays no lead fuel, spark plug fowling is much less of a problem than it was in the past.
I've had the same set of AC 43N's in my 66 425 HP car for the last two years. I drive it in slow traffic to/from local car cruise-ins and hardly ever get on it. No plug problems.

the 45 XLS is about one step hotter than a N-43 because the tip if farther into the chamber and sees "fuel wash" which cools the plug slightly.

[Bill M.]

Re: 65' 396/425 Spark Plugs

Russell-----


If it were me, I'd be using a Champion RN14YC.

Joe: I've been using RN12YC for years. Did you pick the hotter range to reduce fouling? Have you tried the 12s?

[Clem Z.]

Re: 65' 396/425 Spark Plugs

the problem with BBC plugs back in the day was oil fouling because the ring package was not very good on oil control. with a fresh engine with proper oil control rings and unleaded gasoline BBC plug fouling should not be a problem now days with the TI ignition

[Joe L.]

Re: 65' 396/425 Spark Plugs

Joe: I've been using RN12YC for years. Did you pick the hotter range to reduce fouling? Have you tried the 12s?

Bill-----


I've used both the RN-12YC and the RN-14YC (also, RN-12Y and RN-14Y before there were copper core plugs). I found the RN-14Y to be a little better for the sort of driving I did at the time.