Black spot on spark plug- causes?

[Bee1971]

Why are you running a 650 cfm carb on a modified 440 ?

The 25 spark plugs look good on the heat range , threaded base , like others have stated

However with that 650 cfm carb you might bee running lean at w.o.t.

Put the 25 s back in

Try backing off your total timing to 34 instead of 36

Have you played with jetting ? Or looked into a 750/850 cfm carb

 

[Sonny]

Why are you running a 650 cfm carb on a modified 440 ?

The 25 spark plugs look good on the heat range , threaded base , like others have stated

However with that 650 cfm carb you might bee running lean at w.o.t.

Put the 25 s back in

Try backing off your total timing to 34 instead of 36

Have you played with jetting ? Or looked into a 750/850 cfm carb

Yes to both. Changed the jetting using an air fuel ratio gauge. All the carb “calculators” said 650.?

 

[steve340]

You should be OK with a 650. Don't worry it will be a nice responsive street carb size.
As you said in earlier post you do not intend to go racing.

 

[lewtot184]

the engine in my '69 r/t is the original 440, but has had the unleaded gas conversion using the '906 heads and kb184 pistons. no silly cams and stock intake/carb with a mopar electronic ignition. it's the nastiest burning engine I've ever owned. terminal nasty!!!! I've tried every trick I can think of with the stock carb and every trick I can think of on ignition combo. the nicer I get it to drive the worse it burns. try to clean the burn up and the engine runs rough. but, there is one thing I've done that does help. I found an edelbrock 1407 and "moparized" it. I put a mopar primary throttle shaft in it and all the mopar choke stuff. looks mopar. this carb will burn noticeably cleaner and smoother than the stock 4618 avs. the majority of nasty burn is low rpm; cruise not too bad. I do think the stock intake has noticeable distribution issues. I haven't found anything with ignition to make a noticeable clean-up and that includes timing curve, initial timing, box, plugs, wires. it's all in the air fuel mix and trying to get the worst combustion chamber on the planet to burn. I did find that heat helps but I do get a little jitterey about 200f temps.

 

[Sonny]

the engine in my '69 r/t is the original 440, but has had the unleaded gas conversion using the '906 heads and kb184 pistons. no silly cams and stock intake/carb with a mopar electronic ignition. it's the nastiest burning engine I've ever owned. terminal nasty!!!! I've tried every trick I can think of with the stock carb and every trick I can think of on ignition combo. the nicer I get it to drive the worse it burns. try to clean the burn up and the engine runs rough. but, there is one thing I've done that does help. I found an edelbrock 1407 and "moparized" it. I put a mopar primary throttle shaft in it and all the mopar choke stuff. looks mopar. this carb will burn noticeably cleaner and smoother than the stock 4618 avs. the majority of nasty burn is low rpm; cruise not too bad. I do think the stock intake has noticeable distribution issues. I haven't found anything with ignition to make a noticeable clean-up and that includes timing curve, initial timing, box, plugs, wires. it's all in the air fuel mix and trying to get the worst combustion chamber on the planet to burn. I did find that heat helps but I do get a little jitterey about 200f temps.

Wow thanks. Glad I’m not alone.

 

[lewtot184]

i have a 440 in my '65 coronet; dual quads, cam, eddy heads, headers, FBO box. I can get this thing to where the plugs burn scary clean. night and day difference between the two cars. this car has a better intake manifold and I cruise off the small primaries of the rear carb. the primaries have about 60+% of the venture area has the 440 avs. so i'm pulling the same amount of air thru smaller venturii's and I think that gives a better mix; more velocity. I do think the edelbrock chamber and angle plug do burn better. ignition differences and minor timing differences don't play a part.

 

[Wietse]

Is it not that the dark spot on the ceramic is caused by the fact that it is facing away from the flame?
So the dark spotted section of the ceramic is facing the cylinder head and does not really get in direct contact with the flame path?
As the other side is burnt nice and clean....
As per the story of 4secondsflat, only the first thread of the 25's plugs looks burnt, which is a sign for being a too cold plug.
The 23's have 2-3 threads burnt which is more likely to be the correct plug for your application by looks, but strange that this shows on an even colder plug then compared with the previous ones...