Carburetor Advice

[bandit]

Running a 383 with a 3310 4 barrel Holley. This thing is running way too rich. Actually burning my eyes at idle. I have backed the adjustment screws out to about 1/2 turn out from full seat on both sides and have backed down my idle screw so I am at about 900 rpm. It has an electric fuel pump that was running at 8 psi initially so I backed it down to 6 psi today. It helped a little I think but it is still running way too rich. All I can assume at this point is that the jets were changed out before and are too big. The guy who used to own the car raced it on the 1/4 mile so I'm sure he messed with it. Does anyone know or have a recommendation for a good jet size on this set up?

 

[67 coronet]

it may not just be a jet thing.could be a blown power valve dumping fuel,or several other problems.with minor mechanical skill you could rebuild it and start fresh.

 

[440roadrunner]

What are you doing with timing? You want as much initial as you can stand

1 Just below kicking back on the starter
2 Just below low RPM knock (ping)

THEN set the idle, and don't "back out" the screws, instead actually ADJUST them. With the engine warm and idling, back them out until you know they are rich, then EASE them in until the RPM peaks and falls off, then just touch them back out so the RPM peaks, or use a vacuum gauge. You want the the final setting to nudge a little on the lean side of the peak

You'll probably have to go back and forth several times, resetting the idle speed as needed to keep in the ballpark.

Jetting should not affect idle. Leaking power valves WILL

 

[bandit]

Thanks. Timing is suspect. I have a timing light but the mark is way below the gauge so I have been timing it by feel. Right now I have the timing retarded right around the middle of stumble and max rpm if that makes sense.

Can you clarify "you want as much initial as you can stand"? I was turning the distributor by feel so the rpm's were maxing then I was retarding it to about the middle. Is that correct? This might explain a diesling problem I have been wrestling with along with a hard start when hot. I probably need to just go get a pressure gauge.

Do you know what the vacuum should be at on a 383 4 barrel in a 70 Charger and also where to hook it up?

 

[67 coronet]

kicking back on the starter is when you are starting it is not a smooth sound,sort of a pulsation when trying to start.bump up timming untill when you start it,it seems like the starter is laboring.then back it off a degree or 2,very small amount until it starts smooth again.then drive to check for pinging.

 

[bandit]

I'm sorry I am still a bit confused. Are you talking about it being retarded or advanced to get to the point of starter kickback? My starting point is where I get max rpm's.

 

[67 coronet]

I'm sorry I am still a bit confused. Are you talking about it being retarded or advanced to get to the point of starter kickback? My starting point is where I get max rpm's.

advancing the distiributor untill the starter labors when starting in a sort of pulsation sound.you need to bump up the timming a little and start the car.if smooth,shut off and repeat until your starter has a rough time starting the eng.when you get to that point retard it back a degree or two until it dosnt labor.normally gets you close to max advance.drive to check for any pinging,retard more if needed.

 

[Meep-Meep]

A leaky power valve can certainly cause a rich condition. Also a high float level. Or if you have the wrong power valve for the amount of idle vacuum. Check the vacuum in gear and spec the valve accordingly. The primary jets should be 72 if I recall. If you have a stock or very mild 383 I'd reconsider running the 780. That's just way too much carb for street use where you rarely see over 6000 RPM.

 

[bandit]

I think I got it. I advanced it until the starter was laboring then backed it off. So far it seems my over rich problem is better. The car reved beautifully in neutral and ran great at low rpm after setting it but when I step on it you can here what I believe are the lifters or valves rattling loudly and it gives a slight miss. I kept backing the distributor off and finally got rid of the rattle and miss but I liked the smooth powerful rev at idle it gave before I started backing it down. Is this because of a low octane level? I drive into WI to get non ethanol but it is only 91 octane. Do you think I should be adding some octane booster so I can advance it some more again?

BTW I think I may have a leaky carb too and will ultimately need a rebuild. Car starts very hard when hot but will fire up if I push and hold the pedal to the floor to open up carb.

 

[RustyRatRod]

Cool. Progress is always nice. Maybe I missed it, but I didn't see anyone say anything about a vacuum gauge. You need to put one on a manifold vacuum source and get a reading. Here. This is straight from Holley:

The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to “time” this system’s
operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number “65” indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501, should be used when determining the correct power
valve to use. A competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8” Hg vacuum reading divided by 2 = 4 power valve.
Since there is no #4 power valve you should use a 3.5.
Most of the popular Holley “Street Legal” and “Street
Performance” carburetors incorporate a power valve blow-out
protection system. A special check valve is located in the throttle
body expressly for this purpose. This check valve is
designed to be normally open but will quickly seat to close off
the internal vacuum passage when a backfire occurs. Once
closed, the check valve interrupts the pressure wave caused by
the backfire, thus protecting the power valve.
If you have a carburetor older than 1992 (or you have experienced
an extreme backfire) and expect a blown power valve,
use this simple test. TEST: At idle turn your idle mixture screws
(found on the side of the metering block) all the way in. If your
engine dies the power valve is not blown.​

​

 

[bandit]

I did hook up a vacuum gauge to try and assist in timing but the needle on the gauge is bouncing way to much to be useful. It is one of those gauges with the manual pump on it(loaner from Autozone). Not sure if that makes a difference but it was useless. I hooked it up to the advance port on the carb and tried the brake booster line off of the manifold and same thing. You can see it in general go up and down as you tweak things but it bounces between about a 5-8 psi range rapidly so cannot get an accurate reading

 

[RustyRatRod]

Did you try the vacuum gauge after you adjusted the timing?

 

[bandit]

I just went out and rechecked and same thing. I even pushed it up to full advance and it keeps bouncing. I am going to try some octane boost and keep it a little advanced and see if it helps.

 

[bandit]

I just re-read the last sentence in your other post. My engine does not die or sputter when the mixture screws are bottomed out. Looks like a blown power valve from what that says.