need help with engine tune severe engine bog after switching to aluminum heads

[440charger68]

68 charger 318 had some old 302 cast number cylinder heads and switched them out for a set of aluminum edelbrock rpm heads, i have a holley 600cfm carb with a edelbrock air gap intake. Cam is a lunati vodoo with a 475intake 494exhaust. So if i punch my gas to the floor my car goes into a deep bog and will die some of the time, everynow and then it will back fire through the carb too. While im on the street doin about 40 or 50 and i punch the gas it will also go into a bog really stressing me out any expert advice? i tried goin up a jet size but its still bogging

[Chryco Psycho]

sounds like ypou need more fuel in the accelerator pump system , so bigger squirter & possibly a different pump cam as well

[Budnicks]

Just spit balling here... like Psycho said plus, Maybe more ignition timing also...  Does it still have the points? is the dwell correct? Is the air gap correct {0.008"} if an electronic ignition ? Use a non magnetic feeler gauge... Jetting & fuel delivery first.. then maybe ignition timing...

[440charger68]

my old squirter size is 31 thinkin about goin to 37 and i just bought a kit of pump cams. i had a old holley in my garage with a 32 i installed the nozzle and it made a little less bog so i think goin to a 37 would be a good route. What has to be gapped at .008? and yes its electronic.

[Budnicks]

my old squirter size is 31 thinkin about goin to 37 and i just bought a kit of pump cams. i had a old holley in my garage with a 32 i installed the nozzle and it made a little less bog so i think goin to a 37 would be a good route. What has to be gapped at .008? and yes its electronic.

The "Air Gap" in between the reluctor & pick up... The Reluctor {spelling?} little star looking thing on the distributor shaft & it's magnetic pick-up... this is a pitcher of the pick-up... see the little piece of metal in the "center that needs to line up with a point on the Reluctor" , bump the engine over tell 1 of the points on the Reluctor lines up with the little metal stub sticking out of the center of the magnetic pick-up lines up, make sure to turn off the ignition key & loosen the Pick-up mounting plate screws just slightly, use a flat blade screwdriver to adjust the plate, then make absolutely sure to use a non-magnetic "brass/bronze" 0.008" feeler gauge adjust it to have 0.008" "air gap" between the 2 pieces {Stub in center of the magnetic pick-up & the point on the Reluctor}, re-tighten the pick up mounting plate screws, check gap, if good, then button up the distributor...

[71bee]

I would seriously suspect carburetor jetting or power valve size. are you using a Holley 4160 or 4150? the 4150's are always the better choice. whats your intake vacuum at?

[Challenger340]

What was the wee-18's compression Ratio with the Iron 302's ?
What is the 318's compression ratio NOW with the Eddy's ?
Is it the öriginal '68 318 Pistons, or has the Engine been rebuilt with new pistons ?

If nothing else changed, you will need a TON more incipient Heat for flamefront propagation/lead Timing going to the Aluminum Heads, and the problem is compounded at lower Compression ratios below 9.0:1.
You can keep trying to "cover it" with more Fuel, hope for the best...

[440charger68]

Dont know with the 302s but with the new cylinder heads it's a little over 9 :1 and for vaccuum I been so busy with work haven't checked yet  but I will this weekend I will be workin on her, just got my new squirter and a set of pump cams from summit. I thought these heads would be straight bolt on power??? My motor was rebuilt about 30000 miles ago stock rebuild pistons sit .025 below the deck.     

[Challenger340]

Dont know with the 302s but with the new cylinder heads it's a little over 9 :1 and for vaccuum I been so busy with work haven't checked yet  but I will this weekend I will be workin on her, just got my new squirter and a set of pump cams from summit. I thought these heads would be straight bolt on power??? My motor was rebuilt about 30000 miles ago stock rebuild pistons sit .025 below the deck.     

OK, how did you "measure" that a little over 9.0:1, or, is that a "theoretical" ?

Did you do actually CC a Downfill Volume check at TDC when the Heads were off ?

What YEAR are the Pistons ? original '68 ?
or,
has the Engine been rebuilt with new Pistons ?

The reason I am asking, is because any jobber Pistons, are inherently LOWER than you may think ? especially when then using a Composition Head Gasket which is all that is available for the small Blocks ?
And if you are substantially below 9.0:1, which is what I suspect, you are gonna have a very tough time covering off the Bog on the Aluminum Head with that port volume ?

Do you have a Choke Valve on the Carb ?
Try wiring it half shut, jump on it from a Roll, see if that helps ?

[440charger68]

i took all my engine specs and used a compression calculator off summit. Engine was rebuilt with new pistons, so if upping the squirter size and accelerator pump cam doesnt work what do you recommend? Shaving the heads should solve the problem shouldnt it?

[greenpigs]

So I take it you can't use a thinner head gasket to help a little?

What is the CC of the RPM heads & like said did you measure the iron heads CC? 

Challenger340 is way more up to speed on this than I am, but REAL measurements are needed before I would go milling the heads.

[BSB67]

68 charger 318 had some old 302 cast number cylinder heads and switched them out for a set of aluminum edelbrock rpm heads, i have a holley 600cfm carb with a edelbrock air gap intake. Cam is a lunati vodoo with a 475intake 494exhaust. So if i punch my gas to the floor my car goes into a deep bog and will die some of the time, everynow and then it will back fire through the carb too. While im on the street doin about 40 or 50 and i punch the gas it will also go into a bog really stressing me out any expert advice? i tried goin up a jet size but its still bogging

A lot of pieces of the story are missing.  I suspect that it might be something simple. What all is new?  Did this carb run okay before the head swap?   How does it idle, and what is the idle vacuum?  Do you have a PCV valve?  Did you check to see if the squirters are working?  Do you have a thermostat and is the engine coming up to operating temperature?

[440charger68]

how can i tell if the squirters are working? and the new aluminum heads have 63cc combustion chambers, my old heads were mid 80's 318 heads cast number 302. I dont have a pcv valve and my car ran decent before the swap carb is probably 6 months old. i dont have a vacuum gauge so im not sure, but it idles fine starts right up and sounds great.

[maxwellwedge]

Keep the car shut off.
Remove air cleaner.
Peer down at the squirters.
Grab the carb linkage and open semi-slowly to full throttle. The squirters should be discharging a steady stream of fuel throughout the pump stroke.

Before doing this - make sure the car was running a few minutes before, to ensure the fuel bowls are full.

[440charger68]

squirters are working we tried adjusting the air to fuel mixture and as we started we seated the idle mixture screw all the way in, shouldnt that usually kill the motor?? engine stayed running exactly the same as if the needles were all the way out sounds like a problem

[maxwellwedge]

Any vacuum readings yet?

[440charger68]

no vacuum gauge and i have work in a hour!  i should have a vacuum reading tonight or tomorrow im thinking challenger 340 is right maybe a thinner gasket will help mine is a massive .039 in compressed size. Im just goin to go through it and make sure everything is to spec before i decide to take the cylinder heads off again. i have increased the squirter size and used a bunch of different accelerator pump cams and the hesitation is still terrible almost regret getting these heads!!!  when i punch the throttle it doesnt hesitate as much but when i gently open the throttle simulating my normal driving it starts to bog and will keep bogging till i punch the throttle maybe bad pump idk?

[b5blue]

Too rich will make it fall off also. It should die with idles in all the way. (?) 

[BSB67]

how can i tell if the squirters are working? and the new aluminum heads have 63cc combustion chambers, my old heads were mid 80's 318 heads cast number 302. I dont have a pcv valve and my car ran decent before the swap carb is probably 6 months old. i dont have a vacuum gauge so im not sure, but it idles fine starts right up and sounds great.

Okay, no PCV valve.  Probably not a good idea, you should have one.  If not, you need two free flowing breathers on on each valve cover.  Anyways, do you have the PCV port in the back of the carb, under the fuel bowl, plugged?

[440charger68]

I have breathers on the valve cover just no pcv valve that goes to the air cleaner. everything is plugged on the carb except vacuum advance.

[BSB67]

I have breathers on the valve cover just no pcv valve that goes to the air cleaner. everything is plugged on the carb except vacuum advance.

It goes to engine vacuum, not the air cleaner.

[71bee]

I have breathers on the valve cover just no pcv valve that goes to the air cleaner. everything is plugged on the carb except vacuum advance.

It goes to engine vacuum, not the air cleaner.

yup!

[BSB67]

Although I don't know what your problem is, I do suspect that it is the result of something that you have touched or done during the head installation.  It is not the heads themselves.

With the bits and pieces of info that you have supplied, here are some general rules:

1) The WOT hesitation is from a lean condition....either to little fuel from the squirters, too little fuel from idle/transition circuit, or a vacuum leak
2) Light part throttle hesitation is from a lean condition....usually too little fuel from idle/transition circuit, or a vacuum leak
3) Idle does not change when idle mixture screws are seated is from a lean condition......usually a vacuum leak

Also, IMO, the symptoms you describe are not from minor tuning imperfections.

For #1 above: If it is a double pump carb, be sure that the front and rear squirters  (i.e. 4 streams of fuel) are providing solid steady fuel when you open the carb to full throttle (car off, looking straight down the carb).  Have you taken the rear fuel bowl off recently and possible not put the pump linkage together correctly?

For #1 and #2 above: Idle/transition lean condition would be internal to the carb, and could be from dirt.  Accidental dirt in the fuel line during head installation?

For #1, #2 and #3.  Vacuum leaks can be from the carb, open carb vacuum ports, leaking vacuum lines, or intake manifold.  Did you remove the pins from the end rails? Did you use a gasket or just silicone for sealing the end rails? Is it possible that the end gaskets are holding the intake off the head?  Carb base gasket completely covers/seals the carb base to the intake.  You did plug the Carb PCV port. Carb fuel bowl vents are open. 

If you have 15" vacuum idling at 750 rpm you don't have a vacuum leak.  If you put your hand over the carb at idle and it stalls without the idle speed first increasing, you don't have a vacuum leak.

If you can give us several close up pictures of the carb from all angles that might help us.

[Budnicks]

sorry double post

[Budnicks]

Some things may not apply exactly to your problems but, It may help with a diagnosis if you list exactly what all detailed changes were made, what is you specifics timing    camshaft installation     retarded, advanced,  straight up or what     Did you check for proper push rod length    what valve lash or preload     what other changes were made to the carburetor, power valve size, jets sizes, metering plates, secondary vacuum springs, acc. pumps or cams, discharge nozzle sizes     have you done any mods to the distributor    what is you total timing with all the advance in  what is your initial timing    are you using a vacuum advance    if so, is it an adjustable type & did you do any adjustments    have you done any advance spring changes, weights or bushing in the distributor  ,   the more information you can add, it will maybe help someone to give you a decent diagnosis & solution to the problem...