Should I go to a colder plug

[butch27]

I'm running an Edelbrock600 on a 302" Ford bored 30 over. I tuned the darn carb down to lean and yet  the Autolite 45 plugs gapped at .040 are still getting carboned  up.  Should I go to a colder or hotter plug? We just drive it short distances to club meets.   Thanks

[kb426]

Explain "turned the carb down to lean".

[chimp koose]

a lot of those carbs have a pretty rich idle circuit that could use larger idle air bleeds to lean out the idle circuit.

[butch27]

I put smaller main jets in and used the Edelebrock chart to reduce and get better millage. The idle jets from what I understand ONLY adjust the IDLE air fuel.?

[crdnblu]

We really need more info to help in your decision.  What is your engine combination? (Cam, manifold, initial timing BTDC, vacuum reading @ idle......)  Have you checked your choke operation to insure that it is going to full-open w/ a warmed up engine?

[butch27]

Stock cam bored .030 over . Timing is 14 before. In a T bucket so not a whole lot of engine mods. Mallory dist. (electric). The darn thing just runs too rich and carbons up the plugs.  I've been told to go colder than the 45s I have down to as much as 32 or 22. Doesn't sound logical to me.  Car runs fine and starts great.  JUST a lot of carbon.

[crdnblu]

Did you check your BTDC initial timing with your vacuum canister disconnected, (if your Mallory distributor has vacuum advance)? Have you verified that your fuel pressure is in spec for your Edelbrock carb; they are sensitive to too high fuel pressure.  Additionally, have you verified that your float levels are in spec per the carb's installation instructions?

Normally, a carb change to a 600cfm unit should NOT require a hotter plug; never a colder plug, if the plugs are showing carbon soot. A hotter plug change may mask other problems.........

Again, what's your vacuum reading @ idle?

[kb426]

I seem to remember that someone had a vacuum leak on the bottom side of the intake runners that caused something similar sometime back. Now, because it's a sbf, are you sure it has the correct timing mark for the balancer? There's about 4 different ones that I know off. Weak ignition is one of the most common items that I run across. I had a bike that was testing my skills several years ago and it was finally traced to to high of float level.

[butch27]

I haven't checked reading yet. Got to get a gauge.  Yes I had the vacuum disconnected.  I'm running a Jeg's chrome Ford fuel pump but no pressure gauge. I think it puts out about 8 lbs.

[crdnblu]

You could have a high fuel pressure issue; from the Edelbrock manual:

"Fuel Pumps and Pressure
Avoid extremes in fuel pressure. At IDLE, there should not be any more than 6.0 psi; if the vehicle has
an adjustable fuel-pressure regulator, set it to 5.5 psi."

[butch27]

THAT make sense .. will I have to cut into the stainless fuel line to  check the pressure?

[crdnblu]

I would say "no"; you should be able to find one of these combo fuel pressure/vacuum test gauge kits locally @ a reasonable price, then just match up your fuel-line fitting(s):

http://www.ebay.com/itm/New-Fuel-Pump-Vacuum-Tester-Gauge-Leak-Carburetor-Pressure-Test-Tool-kit-Case-/141720843989?hash=item20ff3876d5&item=141720843989&vxp=mtr

Then you could also check your vacuum @ idle......

[Glen]

if that is a 1405 or 1406 i would guess the metering rods need to be a step leaner.  I have put two of those on little SBC stock motors and had to change them out to clean them up.

http://www.edelbrock.com/automotive/misc/tech-center/install/1000/1404_manual.pdf

[butch27]

I did go leaner on the metering rods. I'll keep working.

[wayne petty]

i should mention...

lets perform some tricks..

cold engine.. shop towels..  air compressor.. carb cleaner spray..

slowly turn the idle mixture screws in counting the turns til they are LIGHTLY seated.. then remove them and the springs..   spray a short blast of of carb spray in the idle mixture screw hole.. followed instantly by a shot of compressed air..  this will wash and blow the dirt out of the idle air bleeds and the idle feed restriction..

do not overdo the spray into the hole.. you don't want to fill the engine with carb spray..  the shop towels can mop up any spills.. .. you may want to put one over the carb top if the air cleaner is off.  there will usually be some spray coming up just behind the metering rod covers..

not that i have confused everybody..














there are a few things..

at idle.. the idle transition slots are supposed to be only fractionally exposed.  this prevents any fuel from being pulled out as a large area of the idle transition slot is above the throttle blade.  

all the idle fuel is pulled thru the idle feed port and around the idle mixture screw tapered end. ..  this limits your idle fuel..  usually slightly lean.

when you open the throttle.. you start to expose the idle transition slot. the fuel is progressively pulled out to keep the air fuel ratio slightly rich so you have decent acceleration.    this is before the main circuits start flowing.  so no jetting or metering rod changes effect will effect any idle or idle transition engine speeds below about 1200 to 1400 rpms.

somewhere in that range.. the main circuits start flowing as the air flow past the booster venturi's is enough to lower the pressure and start to pull the fuel up and over..   but the idle transition circuit is not done.. it will work up thru 2000 to 2400 depending on the carb size and engine displacement.

if your engine is fouling out the spark plugs at lower RPM.. or at idle..  please perform the carb spray and blast of air..  you may end up needing to pull the top off the carb and the primary boosters out..  i know i am not supposed to do it. but i have found that a chunk of 0.023" stainless mig wire works perfectly for 90% of the carb passages.  to make sure they are not plugged.. if they are corroded.. dirty.. fuzzy.. they will be smaller than design spec and will either reduce the fuel is its dipped in the fuel.. or richen up the idle circuit if the air bleeds are clogged or restricted..

if your engine won't idle with the idle transition slots just barely uncovered. check your PCV flow calibration..  warmed up at idle.. blocking the PCV flow should reduce the engine RPMs between 50 and 70 RPM.   if the rpms drop less.. you need more PCV flow.. if the rpms drop more. you may need to go larger..

if you have a big cam.. and are fouling the spark plugs because you cannot get it to idle just on the idle transition circuits.  just for fun.. and to figure it out..  in your PCV hose.. between the carb and the PCV valve.. install a TEE.. and a fine thread metering valve..  this will allow you to fine tune the idle speed.. with the primary throttle at the proper setting just barely exposing the idle transition..  this is just for testing..

with larger displacement motors one really needs to look at the exhaust gases with an air fuel ratio meter.. as you slowly accelerate the engine from idle to 3000 and back to idle..  if the idle feed restriction is too small.. the engine will go lean off idle..  carefully drilling the idle feed restriction one drill size at a time.. on both sides..  making sure the chips are blown out.  and retesting..  one should be able to slowly accelerate the engine from idle to 3000 RPMs and back to idle and be able to hold any rpm and accelerate again slowly..

with motors smaller than 355 cubic inch which i think is where most idle feed restrictions are sized at..  may need to be reduced to cut down on their flow..   how to perform this magic when they are pressed in?

i wish edelbrock had various calibrations of primary boosters available for purchase..

i hope this helps..  and since its really early in the morning it might not make any sense..  i  could actually be asleep.