Only 4 plugs carbon fouled

[butch27]

Still trouble! On my Ford 302" the number 2 and 3 and 5 and 8 are carbon fouled  badly after a 80 mile run, the other 4 are just WHITE and super clean like they we never used.  I have a Weiand dual plan manifold. I checked each wire and they are sending fire to each plug. Distributer shows no sign of jumping fire.  HELP-- Uses lots of gas.

[butch27]

Oh: Also running an Edelbrock 600 with NO choke.

[Charlie Chops 1940]

Couple things...

Did it misifre- that is, run poorly or just not get that bad yet?

Did it seem to use an unusual amount of oil?

If either I might  suspect valve guides.

Fresh engine or anything that set this off?

[WZ JUNK]

I am not a Ford guy, but I did work on a Mustang once that had an unusual situation like yours.   I still have not thought it through, but I fixed it.  The cam had been changed and the firing order of the engine was different than it was originally.  I changed the spark wiring to the new firing order and it solved the problem.  I have no idea if you have a similar problem but since this is so unusual, you might visit with someone more knowledgeable and find the other possible firing order.  The engine I worked on was a 351 but I believe it is the same family.  Just a shot in the dark.  \

John

[butch27]

It starts and runs good. It just has a slight  mis-fire at cruising speeds. I clean the plugs and after any run they end up fouled with carbon. Does not use oil that I can note. The oil gets black quickly.

[butch27]

I just noticed --- It's firing on every other cylinder

[chimp koose]

is the carb going rich on one side causing the cylinders on that side of the dual plane to go rich?maybe the idle mixture screw is backed out?Did a jet fall out. What type of carb are you running?

[butch27]

It's a Edelbrock 600 carb. How can it be rich on one side if it's hitting every other plug.?

[WZ JUNK]

I got this off of a Ford board.

Your cam determines the firing order.
289/302 cam: 1-5-4-2-6-3-7-8
351w/302HO cam: 1-3-7-2-6-5-4-8

I noticed that this information does not exactly agree with the cylinders that you are having problems.  That's all I have.

John

[416Ford]

i know you had carb problem before, has the car run with this set-up in the past and this is a new problem or is it a new set-up and having problems?

Have you check for a vacuum leak? I know Chevy used to have a problem with the low portion of the intake if it had a vacuum leak and I can assume all intakes would have the same issue.
What are you using for a distibutor? If you are only firing hot on every other cylinder that would cause fouled plugs also.

All comment and questions are for more info. I am not a pro.

[wayne petty]

sorry.. i should have looked at this yesterday.. i saw and did not click..

lets start at the idle mixture screws...

do they both work... will turning either in cause the engine to stumble... do they seem to adjust the idle fuel mixture...

can you use a mirror and look down the primary bores and the secondary bores while idling.  there should be NO FUEL DRIPPING or pouring out of the primary boosters at idle..

how fast is your idle..

do you have a PCV or a power brake booster hose that might be incorrectly hooked to one side of your dual plane intake..  what.. i think your intake is a dual plane... it has a divider between the left and right halves..  this works better in street driven low to moderate RPM engines.. but that just what i heard.  and my hearing is bad..
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how good with screw drivers are you... can you loosen the little screw that holds the primary rod cover in place and rotate it to the side and check the up down motion of the primary piston..  is there any chance of you getting the engine started and moving the hold down plates to the sides to verify that at idle there is enough manifold vacuum to suck them all the way down.. there are 5 different pairs of springs available.. so the engine idling manifold vacuum reading just has enough suction to bottom the piston out on the spring.  this is probably in drive at idle by the way..  this allows you to tip into the throttle to start to raise the primary metering rods out of their jet..  but also allows them to be fully seated at cruise so you get the best fuel economy..  i bet that's not written in the manual..



i can get deeper but i don't want to put everybody to sleep..


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if there is ANY issue at all with the idle mixture screws...  engine off.. slowly turn them in to LIGHTLY Seat them.. counting how many quarter turns it took to seat them..  this will only save a few minutes when you are done but those can be frustrating minutes..


remove the idle mixture screws and springs..  spray in a blast of carb cleaner.. use the good stuff.. B 12 chem tool spray..  most parts stores have some kicking around on a top shelf.. http://www.berrymanproducts.com/products/cleaning-degreasing/b-12-chemtool-carburetor-choke-and-throttle-body-cleaner/  this is NOT CARB DIP.. and don't get any in your eyes.. trust me.. it HURTS... .. now that you have blasted the idle mixture screw hole. follow up with a big blast of compressed air..  another blast of carb cleaner and another blast of air..  do each hole at least twice..  don't let the carb spray evaporate in the passages.. blow it out while its wet..

a few pictures..



and yes.. i actually ground away an old afb primary booster for this image.. the rest of the carb was water damaged..






in looking at this diagram below.. do you see the idle air bleed and the idle bypass air bleed.. if either of those is clogged you will get rich idle and rich idle transition  and a rich low speed cruise.. as it may BE pulling way too much fuel thru the idle feed restriction and out of the idle transition slot..
blowing carb spray followed by the compressed air will USUALLY blow dirt and grime out of the idle air bleeds and idle feed restriction without needing to take the carb apart.

but note..  that there is also a high speed air bleed..  if that gets clogged it will cause the primary main circuit to pull TOO MUCH fuel.. i have not studied on how to clean that out other than remove the top of the carb and take the primary boosters out to clean the various passages...



you will want to check that the throttle blade screws are actually tight and when you back totally off the idle speed screw with the choke fully open and make sure they are centered in the bore.. if they are not centered.. you could have fuel distribution issues as the left and right side of the carb are NOT in sync..

please post what happens.. does any of this make any sense..

[butch27]

O.K. more info: I have the 1969 Ford distributor with points . The vacuum line is hooked to the Higher port on the carb.  I'm at 12 degress BTDC and 27 degrees dwell. I turned the idle screws all the way in and backed out 3 half turns. Seems to idle fine. I have a PCV valve in the left CalCustom valve cover running to the carb base.  I just pulled the distributor and put it back in  to make sure I had the correct teeth engaged. It has always run RICH. I went down one size on the needle valves and the secondary jets.

[chimp koose]

the cyl 2,3,5,8 would be the ones fed by one side of the dual plane intake   1(5)4(2) 6 (3) 7 ( is the firing order and the bracketed numbers are the ones fed by one side of a 180 degree dual plane intake. If the primary on the side feeding the rich ones has an over rich condition like an idle mixture screw too far out or a missing main jet or a metering rod that will not drop you will get fouled plugs on that side of the intake.

[wayne petty]

chimp is totally correct.. i forgot to add that with a dual plane carb.. .the left and the right sides of the carb are TWO different carbs...

if you put the carb on backwards and had a way to hook up the throttle linkage.. you would find that you are fouling out the other cylinders..

since the idle circuits seem to be working.. it must be the main circuit.  that is totally separate from the idle and idle transition circuits..

with a mirror.. look down the primary bores for dribbling from the booster legs.. that would indicate a leaking needle and seat causing a higher than normal fuel level and can be the cause of your issue..

pull the covers  over the metering rod like i described see if they are free to move...

if those are .. well pull them all the way out and rip the top off the carb and the primary boosters out to check the high speed air bleeds...

you can also check the secondary air bleeds...

there is just a whole bunch of stuff.. do you have both edelbrock manuals for that carb.?

say .. here is an idea.... got a timing light...  is this a remote coil with a coil wire to the cap.. hook the timing light to the coil wire.  aim the timing light down the primary side of the carb.. and either looking. but i use a mirror.. and bring the Rpms up.. see if you are getting equal amounts of fuel from both sides...  the timing light strobes the fuel making it easier to see the droplets.

and now i know how i am going to eventually get video of the idle circuit and the idle transition circuit flow in operation.. drill a carb spacer and mount cameras and strobe lights in it.. thank you for making me think..

[Mac]

It's not like I don't have my own fueling problems re: Edel. carb but I can tell you they don't like high pump pressure. 4.5 to 5 lbs. is about right.