Carb Advice, Should I go to Holley/QF/Speed Demon

Banzaiii67 · Dec 3, 2014

Start off by thanking all the members on this site, everyone is so helpful~!

1967 Plymouth Satellite

Engine is a 383, Comp ratio is 9.1:1
Heads are fresh 516's w/ 2.08/1.74 valves
Cam is a Comp XE274H cam. 230/236 Duration on 110 LS
Performer RPM Intake
FBO Ignition
Carb is Edelbrock 650 AVS.
Timing is 16*/34* total at 2500
727, 11" 2800 TC
3.73 gears

My problem is... I cannot get on the idle circuit on this Edelbrock Carb, I just have too much cam for it i'm afraid.

Here's what i've tried/know;
-rebuilt and gasketed the carb, cleaned every orifice and confirmed no obstructions in any air bleeds
-set the floats exactly to spec.
-put on the edelbrock heat insulator gasket
-increased initial timing only to have it start detonating at 20* so I back it off to 16*
-ran vacuum advance off the manifold vacuum line
-99% sure I don't have any vacuum leaks
-metering rods suck down orange springs and pop up without trouble
-tighten/loosen the secondary air door

If it back the idle speed off to lets say 550-600 rpms, I can start having a response from a/f mixture screws, so I'm exposing too much of the the transfer slot.

All things considered, the car runs pretty hard, and doesn't have any issues outside of the idle quality.

I suppose drilling the primaries or altering the idle feed restriction is the only thing left to try. My fear is permanently altering this may or may not make a difference and I may want to use it again for something else.

Shall I start pursuing a Holley/QF/Speed Demon? Does the 4 corner idle or idle-eze help in my situation? Annular or Downleg...What would you recommend?

lewtot184 · Dec 3, 2014

have you measured the idle jet size? i have played with the idle jet with some success. i wouldn't use manifold vacuum for the vacuum advance. the timed port on those carbs is right at the throttle blade. when the throttle blade lifts your into manifold vacuum.

furyus · Dec 3, 2014

You will be impressed with the power of a double pumper carb like the Holley. I suggest a 750 cfm.

Banzaiii67 · Dec 3, 2014

lewtot184 said:
have you measured the idle jet size? i have played with the idle jet with some success. i wouldn't use manifold vacuum for the vacuum advance. the timed port on those carbs is right at the throttle blade. when the throttle blade lifts your into manifold vacuum.

I haven't. How do you modify that?

super-bee_ski · Dec 3, 2014

X2 with furyus

I think you DO ned more carb....

lewtot184 · Dec 3, 2014

Banzaiii67 said:
I haven't. How do you modify that?

take the top off the carb and unscrew the primary clusters. when you take them out you'll see two brass tubes. measure the opening of the small tube. this is the idle jet. i've seen them as small as .028," which is small. you probably want the jet around .035".

Car Nut · Dec 3, 2014

super-bee_ski said:
X2 with furyus

I think you DO ned more carb....

X3 :yes:

Holley 750 DP

1wild&crazyguy · Dec 3, 2014

furyus said:
You will be impressed with the power of a double pumper carb like the Holley. I suggest a 750 cfm.

This. You are under carb'd and you could use a 4 corner idle.

rumblefish360 · Dec 4, 2014

Your not over cammed.
You are under carbed.

67 coronet · Dec 4, 2014

i switched to a 750 proform double pump on my 30 over 383 in my 67.has amazing throttle responce.still have idle adjust issues,but i am running a old 590 lift purple shaft,so i didnt expect much in terms of idle.

dburnett6263 · Dec 4, 2014

Had similar issues as well as fuel starvation with my EB650 after a .040 over & Comp CL21-224-4 XE complete rebuild of my tired 68 RR 383. Tried everything in the book and some not with no luck. Went to a Holley 770, problem solved. Night and day difference. Except for idle didn't need to touch it right out of the box. Highly recommended. I would agree with above, you are under carbed.

coloradodave · Dec 4, 2014

I'm confused. The poster said the car runs hard and the only problem is the idle quality. How does this equate to being 'under carbed'? Not saying that he wouldn't run harder with a bigger carburetor but his current issue is not being 'under carbed' (is that even a word?). I think Lew offered some good advice. I'd start there.

lewtot184 · Dec 4, 2014

coloradodave said:
I'm confused. The poster said the car runs hard and the only problem is the idle quality. How does this equate to being 'under carbed'? Not saying that he wouldn't run harder with a bigger carburetor but his current issue is not being 'under carbed' (is that even a word?). I think Lew offered some good advice. I'd start there.

what i tryed to offer doesn't cost $300-$500.

Banzaiii67 · Dec 4, 2014

lewtot184 said:
what i tryed to offer doesn't cost $300-$500.

take the top off the carb and unscrew the primary clusters. when you take them out you'll see two brass tubes. measure the opening of the small tube. this is the idle jet. i've seen them as small as .028," which is small. you probably want the jet around .035".

Thanks Lew. I'm going to try this. I assume you just use a bit and drill it out, yeah? Probably start with a .031 and work up if it's .028.

- - - Updated - - -

coloradodave said:
I'm confused. The poster said the car runs hard and the only problem is the idle quality. How does this equate to being 'under carbed'? Not saying that he wouldn't run harder with a bigger carburetor but his current issue is not being 'under carbed' (is that even a word?). I think Lew offered some good advice. I'd start there.

There is some truth to this, although I did solicit advice on whether I should scrap it or not. I do appreciate all the advice from the posters.

lewtot184 · Dec 4, 2014

i have a set of those small number drill bits i use to measure with. the 650avs is basically a 600 with a little larger secondary and adjustable air valve. on the 600's i've found idle jets anywhere from .028" to .033". the 340/383 smog years avs carbs had .031" idle jets and they were fairly lean. from what info i have the pre smog carbs were .035". this may not solve all your problems but it's some place to start. another thought is; did you recurve the distributor or just bump the timing up?

rumblefish360 · Dec 4, 2014

lewtot184 said:
what i tryed to offer doesn't cost $300-$500.

You are correct and I agree on your path for correcting the problem.
Considering the cam size and build of the whole package, he lacks CFM. Which doesn't address the carb issue.

Banzaiii67 · Dec 4, 2014

lewtot184 said:
i have a set of those small number drill bits i use to measure with. the 650avs is basically a 600 with a little larger secondary and adjustable air valve. on the 600's i've found idle jets anywhere from .028" to .033". the 340/383 smog years avs carbs had .031" idle jets and they were fairly lean. from what info i have the pre smog carbs were .035". this may not solve all your problems but it's some place to start. another thought is; did you recurve the distributor or just bump the timing up?

FBO Recurved the dist. Their card spec'd for 18* initial which is if it's hot out i'll start to detonate under heavy load, so I backed it off 2*

lewtot184 · Dec 4, 2014

Banzaiii67 said:
FBO Recurved the dist. Their card spec'd for 18* initial which is if it's hot out i'll start to detonate under heavy load, so I backed it off 2*

ok. then the centrifugal advance should be coming in quick enough, maybe all in by 2000rpm? if fbo wants 18 degrees initial then it must have 9 or 10 degree plate. the vacuum cans are adjustable; if needed.

jeepers007 · Dec 5, 2014

On my 383, with ported 452 heads and a 284/484 purple shaft cam, carter afb 750, I ended up drilling the throttle plates. I played a lot with the carter before I drilled the plates, but that is what finally gave me a decent idle quality for the lumpy cam.

Banzaiii67 · May 3, 2015

lewtot184 said:
ok. then the centrifugal advance should be coming in quick enough, maybe all in by 2000rpm? if fbo wants 18 degrees initial then it must have 9 or 10 degree plate. the vacuum cans are adjustable; if needed.

I have a 10 degree plate.

So, now that I have A/F ratio gauge I can see what's going on. I have some vacuum on the ported vac on the carb. So with 18* of initial timing , I have more like 24-25* initial. (no pinging with non-ethanol 92)

My reading are in 12.1-12.5 range at idle and then I get random drops into the low 11's. Same with part cruise, up in the 12.9-13.2 range and drops into the 11's than back up.

I'm not sure if I understand this correctly, but since I have that much vacuum at on the ported line I am well into the transfer slots, so the idle circuit cannot ever go lean ?? In relation to the distributor, i'm advancing way too early ( pretty sure that's right) so the advance will never can clean up timing so it's runs rich. So the only way to fix it is drill the throttle blades to get back down into the transfer slot or maybe drilling the Idle jets will help, not sure now ?

My buddy (Ford Guy) took one look at my readings and told me to get rid of this carb and get a QF/Speed demon with 4 corner idle and a MSD Ready to run distributor and stop messing with this, It cannot tuned without heavy modification to the distributor and carb. I just don't have $1000 laying around.

Granted it still runs ok, just not perfect. For now I have just plugged the advance canister and ported vac, but the reading are pretty much the same.

Carb Advice, Should I go to Holley/QF/Speed Demon

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