Spark plugs?

[416Ford]

Wondering what plugs I should be using in my 46. Running 302 /C4 77 heads and 68 bottom end. Mainly stock. Edelbrock Performer Aluminum 4V 289/302 and a Holley 600.
Plug seem to be fouling out rather quickly.
I currently have Autolite 26 plugs in it.

[wayne petty]

autolite 26s are 14MM thread.. 0.46 reach extended tip spark plugs..  for everybody out there..

what kind of fouling.. black carbon fouling???

oil fouling... black and wet looking..

crust build up  until there is no room for the gap


a few things not mentioned..  what kind of ignition system... and what have you done about checking if something like the power valve is blown out.. or if the idle speed is set too high and exposing the idle transition slots instead of just the fraction of the bottom of them at idle.


would you like to go thru a few tests.. i will list them, its your option to go thru them or do something else..

first thing..

lets look at the coil primary voltage..  depending on which coil you have..

if you have exposed nuts on studs on the coil.. clip the 12 volt circuit tester clip to the coil positive terminal..  shove the probe into something that's grounded..  so you can see it from the drivers seat.. DO NOT DO THIS WITH MSD box type ignition systems.

depending on the wiring.. you should have power coming on when you turn the key on.. you should have a medium bright light..  
turn the key to crank the engine.. you should have a BRIGHT light..
return the key to the run position.. it should return to the medium bright light.  if you have the duraspark  coil either round or square. shove the probe into the coil positive cavity.. and ground the test clip.. perform the same test.  should be 3 brights.. but it varies on how its installed.


next test.. i usually use a coil output tester (7 bucks at most parts stores. ) as i can do it the coil output test easier..  position the cap end of the coil wire about 1/2 inch from a well grounded metal part and DON'T hang onto the wire.  have somebody crank the engine while you observe the ARC from the end of the coil wire .. should be NICE and bright blue.. SNAPPY..

if its orange and dim..  you have an issue..  please post this and more ignition info.. i will attempt to assist you in diagnosing the issue..


you will want to create a water bottle.. with a small diameter opening.. 1/8" max..  punch a hole with an ice pick..  so you can squeeze some water into the primary bores while holding the engine up around 3000 RPM fully warmed up.. this will blow the carbon off the combustion chambers and piston tops.. when ever i have a fouling issue.. i try to perform this cleaning service.  the engine like i said needs to be at full operating temps..  the engine over 3000 RPMs..  and a trickle of water sprayed in..  the water will turn to steam..  get into the carbon or crud in the chamber and piston top.. will usually blow it out..  please don't hydraulic the motor with too much water or letting it idle before all the water mist has gone thru the motor.


warmed up at idle..  how fast is it idling..  look at the tach.. if equipped..

start turning one idle mixture screw in the side of the metering block inward.. count the fractions of the turn so you can turn it back to the same place..  does the engine idle down and stall ? indicating the idle mixture circuits are the only ones operating the engine..   if it does not die.. then the power valve may be opening.. or the idle speed is too high and the engine is running on the idle transition circuit instead of the idle mixture circuit..  since you have a 302 instead of something closer to a 351.. you may need to lean out the idle transition circuits..  or idle feed restriction..

~~~~~~~~~~~~~~

next step.. back out the idle speed screw on the left side of the carb.. into the base plate at an angle..   see how low you can get it to idle.  you will need to adjust the idle mixture screws also..  sometimes you will need to open the secondary throttle plates.. or some carbs are equipped with a center mounted idle air bypass screw.. its under the air cleaner stud..

at idle.. all the idle fuel should come out of the ROUND idle feed passages below the primary throttle plates....  if you have too much of the idle transition circuit exposed at idle. you will pull fuel from that circuit and foul the spark plugs all the time.  so the idle is close the primary throttle.. open the secondary throttle slightly..  or install a larger PCV flowing PCV valve..

at idle. blocking the PCV flow should reduce engine speed 50 to 70 RPMs at idle.   too small a PCV calibration.. requires more idle throttle opening.. too large an PCV flow. requires too little throttle opening. and it becomes like a giant vacuum leak..

[416Ford]

You are a wealth of knowledge Wayne
Carb was set last year by the engine shop up the road from my work.
I am running a GM Style HDI dist. Switching as soon as I get a stock style one.
Plugs only have about 800 miles on them and they are dry black.

[wayne petty]

the davis style SBF HEI is a decent unit..  for a unitized..

on a budget, you could go to a dura spark unit..  3 wire.. and still run the 4 pin HEI module on a heat sink..  its not hard to make work..  even removing the guts of something like a an already dead  blue grommet duraspark module i have diagrams to perform this..  

are you running FULL BATTERY VOLTAGE to the current HEI..

stick a volt meter probe into the BAT connector on the HEI CAP.. and touch the other probe to the Positive battery post..  post what the reading is..

also post the voltage across the battery positive to negative ..

take the engine running voltage..  14.6 volts..   subtract the voltage reading from the HEI BAT terminal to the positive battery..  probably around 1.2 volts.. HEI ignitions take like 14 amps to operate.

so..

14.6
-1.2
-----
12.4

if you have more voltage drop  than 1.2 volts.. you may NOT have enough current to keep the ignition at full power..
14.6
-4.5 voltage drop.
------
10.1 and not really enough to completely saturate the PRIMARY windings of the HEI coil.



and a warning.. if you have a strange MISFIRE.. find a different used or NON IMPORTED ignition coil for it.. some of the imported from China coils have a weird harmonic RINGING that causes issues and misfiring.. ask idrivejunk he had one that did that..

~~~~~~~~~~~~~

please also use a MIRROR and a Bright flashlight to view down the primary bores at idle.. you should NOT have ANY FUEL dribbling out of the booster legs at idle..  

can you set the idle speed slower.. and see if you can readjust the idle mixtures.. or turn one of them all the way in and see if the engine stalls..  if it stalls the engine at idle.. then the power valve is GOOD..

[enjenjo]

I believe I would try Autolite ASP25BP

[butch27]

Good info here. I was and am having a slightly similar problem.

[wayne petty]

here is the ldle circuit..  note that all the fuel is being limited by the idle mixture screws in the metering block..  the idle transition slots are NOT exposed more than a fraction of an inch.



here is the idle transition circuit. you can see the fuel feeding out of the idle transition slot and the idle feed port..  the idle transition slot is limited by the idle feed restriction..




here is the high speed circuit.. this is where the fuel is only fed by the main circuits thru the main jets ..



perhaps you can see it better in this image..




for those with AFB AVS carbs..