rough idle when hot

[dutch]

where do I start searching for the problem?
my 440 with 780 holley idles fine when cold, both neutral and drive. When warm it runs fine in neutral, but under load it starts to run rough, almost like it`s missing a spark every now and then.   

[Jamiez]

Do you have an ECU?  Maybe it is mounted somewhere where it is getting too hot?  You might try slapping on a different coil/ballast resistor as well....those are the common points of failure

[cudabob496]

May need new cap and rotor for your distributor, if not changed in a while.

[dutch]

all new parts. I have the feeling it`s fuel/ carb related.  I`ve been playing with idle adjustment, but no significant difference.  Underhood temps using headers are serious on these cars... might have something to do with it. Not sure why it bogs under load only though.

[BIGSHCLUNK]

heat deflector under the carb maybe? 

[cudabob496]

all new parts. I have the feeling it`s fuel/ carb related.  I`ve been playing with idle adjustment, but no significant difference.  Underhood temps using headers are serious on these cars... might have something to do with it. Not sure why it bogs under load only though.

float levels?

If did not have problem before you were making adjustments, try to take carb back to where it was before your adjustments.

[hemiken]

Hey Bart, what exactly is it doing buddy ?

I am thinking the stumble could be something to do with your accelerator pump adjustment, you can have a play once you have that adjusted and you can even get the plastic cams in different shapes to fine tune your shot of fuel in the carb with them also, another thing to look at is the center squirt, check what size it is and play with different nozzle sizes too. But check the adjustment on the accelerator pump arm first old mate.

[Chryco Psycho]

Shakers seem to have more heat issues , could be boiling the fule , is the heat corssover blocked ?
 I have also seen problems with the coil , dist pick up [check the gap] & the ECU when warm

[dutch]

Thanks for the ideas.  I did find a vacuum leak yesterday.... A 1 year old rubber cap I used on the dizzy advance connection (on the carb) crumbled when I touched it     I also have a tiny hesitation when I hit the throttle, so I think I will have to look into the acc. pump adjustment first.
Gotta get me some different cams and knowledge first.....
 

[hemiken]

Thanks for the ideas.  I did find a vacuum leak yesterday.... A 1 year old rubber cap I used on the dizzy advance connection (on the carb) crumbled when I touched it     I also have a tiny hesitation when I hit the throttle, so I think I will have to look into the acc. pump adjustment first.
Gotta get me some different cams and knowledge first.....
 

Good that you found the problem buddy the cams are cheap, but the knowledge is priceless once you start reading it may get confusing, i know when i first read it, it was like reading Dutch so then again it will be a breeze for you to read old mate

[Chryco Psycho]

First make sure there is no play in the pump arm , any play will cause a hesitation .
Each pump cam is different , there are some charts online , make sure you have a chart with 2 screw hole positions for each cam . Some cams pump a lot with little throttle shhaft movement so you get a heavy shopt immediatly other have a lesser shot initially but may still pump the same overall volume but with more throttle shaft movement , basically you want the minimal amount of fuel with just enough to prevent a bog .
The other adjustment in the acc pump circuit is the squirter , often just replacing the squirter with a slightly larger one will eliminate a bog initially .
 if it is bogging under load after you are into the throttle you may have the wrong power valve , it may need to open sooner , if you have a 4.5 you could swap to a 6.5" but you want to make sure the power valve stay closed at idle [in gear if Auto ] so if you have 6" of vacuum at idle in gear you cannot use a power valve over 4.5" for example so it will stay closed .
 

[cudabob496]

usually, when one of those caps are bad, I would get a fast idle right off the bat.

[torredcuda]

How`s the vacuum at idle? How lumpy a cam? Do your idle screws have any effect on  it?  You may need to open the secondary throttle blade slightly to lean out the mixture at idle.

[Talkwrench]

Get yourself a vacuum gauge they are priceless, learn to use it. before changing cams just try 1/8 to 1/4 turn out rich and see if it helps. if not start cams.

[dutch]

no clue on how much vacuum. There`s an Engle K65 hydr. cam inside, but I can`t find specs on it anywhere.  The cracked rubber cap was not cracked bad enough I guess, I don`t think it leaked yet.  I have been playing around with the acc. pump adjustment and the bog @ take off is gone now. Accelleration is much more smooth but idle when hot ,especially in Drive ,is still rough. After I test drove it, it dieseled for a second when I shut it down though.... there`s always something huh....
I have been thinking maybe it`s a good idea to put a taller spacer underneath the carb. I currently run a 1/4" spacer and I have the feeling fuel is getting too hot inside the carb...    It has a torker intake and blocked heat crossover.
gotta get me some tools / gauges to measure things... this feels like running in the dark with sunglasses on