My carb tuning adventures

[Ghoste]

Okay, I am trying to tune the carb in my 67 and I am doing some things wrong and some things right but I figured that since it is a common question, I'd post my adventures for everyone to follow.
To start, it is a 67 (heavy cars even by Charger standards) with a 4:10 rear and automatic trans.   Converter stalls at 2000.   This is not rated stall and I'm not changing converters anyway so no sense posting about B&M 3000's and so on.   This is where this converter stalls in this car as checked on the tach.
It is a 383 with 30 over 10 to 1 compression and the MP 284 484 cam in it.   It has a Street Dominator and Holley 3310 750 on it.
Now for the things I have done right.   I replaced the rear metering plate with the block kit and put 79 jets in the rear.   For front jets, after following CP's Holley tuning guide and finding a bone white insulator (colder than stock J11 plugs) I know the primary is lean, so I am bumping up to 74's in the front.   I should go one step at a time but the car seems very lean.   I will count this as something I am doing wrong though all the same.
Now for the power valve.   I do not know what power valve was in the carb when I got it only that it has been changed.   I know this because it isn't a Holley pv.   There are no numbers or markings on it of any kind.   I have an aftermarket 5.5 pv and that is in the carb now.   This is a bad thing because it makes for too many changes at once.   I did it because I do not have ready access to the correct pv, weather is against me and I wanted to make some tests today with the car while I can, the 5.5 pv was in my toolbox, the car already makes very low vacuum so it likely would have been changed to this anyway and at least now I have a known entity for a pv.
The pump cam had also been changed but I have returned the cam and squirter to stock for now.   Same thing for the secondary spring.
This carb is almost brand new and I got it for free which is always a good thing.   On the negative though is that I know nothing about it previously (and no, it isn't stolen).   I can't change that but the smart thing to do would be to make the carb 100% stock first and then make changes.   I do know that it was on a 428CJ Mustang and those motors like to be lean (stock jetting on those things is 66 in the front).
So let's follow along and see what happens shall we?

[Runner]

you know, b&m makes a really good 3000 stall converter    ifyour 383 is anything like mine was a 3.5 powervalve is what i ran

[Ghoste]

Well, I was going to wait for the plug pull to repost but I did find it interesting that you ran such a low pv.

The converter will have to remain a constant for a while.  This car was not to be the project so it is unlikely it will ever get a looser converter.

[Runner]

my vacuum was about 5.5 inches   thats why i ran the 3.5, didnt want it open while i was idleing

[Ghoste]

What cam was that?

[Runner]

mp .484 in a 383  same as yo have?      i dont remember what i have now, i believe its a 6.5 or an 8.5 sence i put more inches,compresion and a solid lifter cam i now have 12 inches of vacuum.

[Ghoste]

That's what I thought.  That low vacuum sure compounds the process doesn't it?
As soon as it quits raining I'm going to put some time on this thing so I can check the plugs again.

[Chryco Psycho]

start with t the power valve , take a reading & get the corerewct valve in there , then the other settings will sort themselves out

[firefighter3931]

start with t the power valve , take a reading & get the corerewct valve in there , then the other settings will sort themselves out

And throw some 78's in the front. It might need some holes drilled in the primary throttle blades to help get the idle manageable with that low vacuum. Is it idleing on the idle circuit ? Do the idle mixture screws have any effect on idle quality ? The 484 is probably a bit much for that particular combo. Something in the 220-225* @.050 would be a lot better inmo.

Ron

[Ghoste]

Well, I'm going in the right direction.  The plugs have a slightly gray sheen to most of the insulator and the beginning of a tan starting.  You could be right with your jet recommendation Ron.  I thought if you moved more than 5 jets from stock, that was bad?

[Chryco Psycho]

generally if you are more than 5 sizes out in one direction [up or down ] something else is wrong but not always 

[Ghoste]

Okay.  Raining again so it will be a little bit before I can try this again.  In the meantime, I'm moving up two more sizes.  Before I swap jets, I'm going to take another cruise and get a variety of vacuum readings.  I know the only one need concern me for power valve tuning is idle in gear, but I want a record of it under a variety.
The cam pretty much has to stay put for now even if it is wrong.  Idle screws do affect idle and the idle speed is under 1000 so I should be out of the main circuit and transition slots, right?

[firefighter3931]

  Idle screws do affect idle and the idle speed is under 1000 so I should be out of the main circuit and transition slots, right?

Yep, you're still on the idle circuit. Try checking vacuum at cruise speed to see where it's at. If the PV is opening under normal cruise speed it will cause problems. What jets does it have on the primary side now ? A vac secondary carb is more difficult to tune under those types of conditions (low manifold vacuum) and the fuel curve is calibrated for a milder combo for the mostpart. I still think you'll need to modify the primary throttle blades with small holes to let more air in at lower engine speeds.

Ron

[Ghoste]

74's in the front, 79's in the rear.

[firefighter3931]

74's in the front, 79's in the rear.

Bump the primary jets up and take it out for a cruise....then check plugs for coloring. Get a vacuum guage inside the car and look at cruise vac readings as well.

Ron

[Chryco Psycho]

try inserting a small diameter wire into the idle air bleeds this may help a lot

[Ghoste]

What am I trying to correct by restricting the air bleeds Neil?

[Ghoste]

Not really an update, just a dumb question.  Those blue gaskets in the newer Holley's are reuseable, correct?

[Chryco Psycho]

yes the blue gaskets are reusable
by restricting the air bleeds it increases the vacuum signal at the mixtur screws , this can make a big difference in how the car idles on low vacuum engines 

[Ghoste]

Is this strictly a hit and miss thing or do you have a specific diameter of wire you would suggest trying?

[firefighter3931]

yes the blue gaskets are reusable
by restricting the air bleeds it increases the vacuum signal at the mixtur screws , this can make a big difference in how the car idles on low vacuum engines  

...or you can drill holes in the primary throttle blades to allow increased manifold vacuum on the primary booster. The problem with restricting the idle bleeds is that it's a temporary fix and what you need is smaller idle air bleeds. Unfortunately, in a vac secondary carb the idle bleeds are of a fixed dimension and non-adjustable. The HP series carbs have provisions for screw in idle and main bleeds. The other option is to fill in (solder) the bleeds and redrill and create a smaller orifice.

Ron

[Ghoste]

Well, I think I need a series of more accurate vacuum readings before I commit surgery to this carb.  I'll stick with the jet change for now and take it for another drive.

The other unknown to all of this is my factory tach.  I should probably rig up something a little more accurate.

[Ghoste]

Finally have some vacuum readings to go with this.  Warmed up and idling in neutral, gives about 9.5 inches at 1000 rpm.  Idling in gear gives 5.5 at 800 rpm.  Reving the engine slightly in gear brings it back to 10 at 1100.  Cruising around yields a pretty steady 15 inches.
So, it's not pulling gobs of air with that 750 and spacer and single plane.  Looks like I'll need to make another power valve change too.

[Chryco Psycho]

I would drop to a 3.5" PV to make sure it stays closed at idle in gear , it would have a 6.5" PV from the factory & it will not stay closed at idle in gear like that

[Ghoste]

That's about the lowest pv I can get isn't it?  Is that very unusual with my combination?

[Chryco Psycho]

there is a 2.5 available , not really unusal especially with an auto