428 Carb Set up

[Chaplin]

For those of running a single quad on a 428, I was wondering if you could post the set-up you are running. I'm trying to get my carb dialed in properly and I am just wondering how others have theirs set up. I realize that no two set ups will be the same and will vary according to geographic and atmospheric conditions, but I'm just trying to get a ball park range of where people have theirs set up. If you have a holley 3310, edelbrock heads, blue thunders intake, comp cams 292H cam and live in Northern NJ, I'd be especially interested in hearing from you.

Please include as much detail as you can, including,

size and type of carb
jet sizes
power valve size
vacuum at idle (if you know it)
accelerator pump size
initial timing/ total timing

cam specs

and any other details you know that you think would be helpful.

Thanks in advance

[ed cougar]

735CFM holley, vac sec, pri.#68 sec.#78 30cc pump, 28 nozzle. Alu. PI int. mech. X fuel pump. Crower Cam .530 int .535 Ex. timing 16* total 38*@2500.

[ed cougar]

Vacuum @ idle 12Hg. power valve 6.5

[Mr.Fixit]

That 292cam may make setup a bit more difficult. I have a second Holley that I had to run with that same cam in a BBC. It has a 3.5 power valve, drilled throttle blades, and more. the low vacuum at idle made it a pain in the rear, ended up much happier with a lower duration cam.

[Chaplin]

Mr Fixit
Here's the interesting thing. The carb is a stock 3310 that had 72 primaries and a 6.5 power valve. At idle, the engine was running very rich and it had a bit of a stumble/bog between 1800 and 2100. I measured the manifold vacuum and it was only 5"/hg at idle (about 950) and 8"/hg at 1100, and 16" at 2200. I called up Holley and they said to first change the power valve to a 2.5, drive it and then if it's still rich, change the jets.

Well, I changed the pv to a 2.5 and drove it around for a while. The stumble around 2000 rpm was much improved, but a new problem developed. When you are cruising in third gear at 2500 or so and then quickly push the gas pedal down, there is now hesitation in the 2800-3000 rpm range that was not there before-it almost sounds like a lean miss. If you gently roll on the throttle, there is no hesitation.

I need to get some longer tubing on my vacuum gauge so I can drive around and see what the vacuum readings are on the road, but I had the following thought: Is it possible that when I am cruising and when the vacuum is highest, the vacuum does not drop enough to activate the 2.5 pv causing a lean condition?

What do you think? And a smaller duration cam may be in the future . . .

[CJ428CJ]

Chaplin,

If you're happy with the cam other than the stumble you refer to, I'd buy and install a new carb before I replaced the cam. I run a fairly lopey cam (Isky .565 lift, 280 adv duration, 232@.050, 108 LC). I pull only about 4 inches of vacuum at idle. I had a Holley 750 DP on it that I never could get to run really well. I pulled it and replaced it with a Demon 750 DP. I had to change the power valve to a 3 inch valve and I reduced the jets by one size. It runs great now with no hesitation.

Bottom line is, your problem seems to be a carb problem and not a cam problem. Lots of other people run cams with the same or less vacuum than you have. And installing a new carb is sooooo much easier than replacing the cam and it's not much more money.

Chris

[Chaplin]

Chris-
I agree- it's definetely a carb issue. The engine idles fine, but I'm just trying to sort out the jetting issues to get it tuned properly because it is running rich and has these stumbles. My reasons for changing the cam are unrelated to the carb issue in that the cam may be just a little too big (244/244 @50 .560/.560) for comfortablly cruising around town, not to mention that it sounds like a pro-stock car at idle

Mike

[RedCSX]

The custom ground cam from cam research is a solid lifter 242/242 @.050 with 590 lift. The heads and intake are really going to be worked over and plan to go with a Mighty Demon carb. I will have the whole set up tuned on the dyno before it goes in the Cobra. Just got off the phone with the guy porting the heads and intake (blue thunder) . He said the intake was very restrictive and needed a lot of work improved the center port by 40 cfm. Told me to check the exhaust that comes with it. Could be very restictive, said he has seen guys lose 100 HP because of the exhaust.

[Todd Hedges]

sorry Chaplin for hi-jacking your thread but...

CJ428CJ
Your cam sounds similar to mine, and I also have a Holley 750cfm carb.(4150HP) I'm having a real hard time with it.

It runs so rich that at a stop light I have had 2 people on motorcycles ask if they could pass because my exhaust was burning their eyes.

What did you set your timing at?
Did you have the Demon carb custom built?
What's your compression? (mine = 10.5:1)
My 428 is at 36* total timing at 3,000rpms.

I think the problem is timing since above 3,000rmps
when all the timing is in, the sluggish, poor responce
dissapears. BUT I'm not ruling out that the carb. may
also be part of the problem. (Jets being too rich)

The last thing is, how do you learn how to optimize the distribuitor (sp)?
I can't help but to think that the weights/springs that control the advance of the timing my be out-of-wack for the motor. I did see a little oxidation on the surface of the weights an I'm concern.

Thanks for any help.
Todd

[decooney]

Hi Chaplin,

As you may recall in our earlier discussions last year, I changed my cam a while back too, but the one I have now has more lift and duration than your current cam. You may not want to change it yet... I'd keep working on it.

With the carb specs/changes I sent you in the email, I WAS able to get it to runs crisp, clean at idle, and from 2000-6000 it runs smooth with no stumble. In fact, I just made the exact same changes to a friends car with an Aluminum Shelby 427 and he is much happier now too. His car runs smoother, less fumes at stops, and much snappier from 2000rpms up.

If you want, send me another email... did you try the changes we discussed, and if so, what happened? Do you have an HP or regular street carb?

[Chaplin]

Duane-
See my second post on this thread, it describes what I have done thus far and the results. I dropped the pv to a 2.5 and set the initial timing to 12, but have not changed the jets yet. The carb is a regular street 3310.

[decooney]

Chaplin,
I think 2.5s are too low for what we discussed. Try 5.0s, with the jets, air filter, discharge nozzles we discussed. Also, my throttle butterflies are drilled too, with the secondary slightly cracked open.

Also, be sure your fuel pressure is not too high. Critical. Do you have an electric fuel pump and regulator? The needle valves will blow off if you get over 6.5 lbs on some Holley's; especially if the needle valves have not been replaced in a while/dry, etc. We just took my friend Marc's car from 7.0lbs at the gauge/regulator down to 6.0 and wallah! His rich mixture problem is gone.

Let me know how it goes.

[rdorman]

I had this huge response all typed and the *&^*ing network logged me off!

Pull the carb and check the throttle blade to transfer slot relationship at idle. You want .040 to .065 of the transfer slot showing below the throttle blade. If you have more close the primary throttle blades to some where in the middle of that range and open the secondaries by the amount you just closed the primaries.

Couple of items. If the tranfer slots are different lengths, this should be replace by Holley under warrenty. There where a few like this. If the secondary idle speed screw is not covered by the intake, remove it and replace it with a screw that can be adjusted with the carb on.

Set the speed by the secondary. Some reasonable speed. Not like I am found of doing, so slow that it lopes really bad! Small adjustment can be made from this base setting using the primary idle speed screw. While you have it off, see how much you have to turn that screw before you either have less than .040 or more than .065 showing. Not a whole bunch is it?

Set the idle mixture for highest vacuum at the leanest setting. It the RPM increases, bring it back down to your base setting before comparing vacuum ratings.

Set the float level. Note if the float level rises as you increase RPM. If so the so is your fuel pressure. 1/32" per psi if I recall. If you can't seem to set the float level with out the fuel pulling out then you can be sure that you need a new needle and seat and are perhaps running way to much pressure.

This all but cured every part throttle, lean, hesitation, cruise, etc issue in my car. Bascally, many of the same issues you are describing! You can also drill the blades but try this first!

This is a fraction of my former response but it is time to go home!

Rick

[CJ428CJ]

Todd,

In answer to your questions:

1. I have my timing set at 24 initial and 40 total all in by 2000 rpm's (light blue and light silver springs, black stop bushing). That sounds like a lot of timing awful fast but it works great and I get no pinging or run on after I shut down. I did double check my timing mark with a piston stop because it seemed like too much timing to me too. I have the aluminum heads which allows more timing. If you have the cast iron you may not be able to get away with that much advance.
2. No the Demon was not custom built. Bought it off the shelf.
3. Compression is 10.25:1.

Have you checked your vacuum with a gauge yet? Having a PV too high can cause it to run way rich (the PV opens at idle causing a really rich condition and then people open up the idle butterflies to get enough air in to allow it to idle - but damn near knocks you out from the fumes).

All I did to optimize the timing was to play around with it a bit. In my opinion, a light car with a large engine will want a lot of advance as soon as possible. As long as you're not getting any pinging or engine run on when you shut it down, then you don't have too much advance.

Also, any carb adjustments that you do (other than the final idle adjustment) should be done with initial timing set at 25-30 BTDC (per the instructions I got with my Demon) even if you have to retard the timing a bit before you can actually drive it (to avoid pinging).

Chaplin, I wonder if advancing the timing will help your situation too.

Chris

[Mr.Fixit]

"Well, I changed the pv to a 2.5 and drove it around for a while. The stumble around 2000 rpm was much improved, but a new problem developed. When you are cruising in third gear at 2500 or so and then quickly push the gas pedal down, there is now hesitation in the 2800-3000 rpm range that was not there before-it almost sounds like a lean miss. If you gently roll on the throttle, there is no hesitation."

Idle was improved cause PV is no longer dumping fuel at idle. The hesitation sounds like an accellerator pump tuning issue. That will result in a lean miss. Accel pump overcomes the temporary lean spot when you mash the throttle, until fuel is pulled from the boosters. If it hesitates right away, try a bigger squirter, if it hesitates after a half second delay, try a smaller squirter to lengthen the pump shot's duration. a 50 cc pump may be needed, (but no need to start there).


"I need to get some longer tubing on my vacuum gauge so I can drive around and see what the vacuum readings are on the road, but I had the following thought: Is it possible that when I am cruising and when the vacuum is highest, the vacuum does not drop enough to activate the 2.5 pv causing a lean condition? "

having gauge visible will definately help you tune it. While cruising at a steady throttle position, the PV should not be opening, it is there for WOT fuel enrichment only. Your manifold vacuum should be nearly atmospheric (at WOT), but you can try a 3.5 PV, see if it makes a difference for that.

" And a smaller duration cam may be in the future . . "

I wouldn't start there, I ended up going to a smaller cam not because of carb issues (I got that sorted out) but because the loss of low and midrange torque. By the time the motor was in it's powerband, it was time to shift; car was quicker with a smaller duration cam. Replacing the carb as some suggested probubly won't help, that one will need setting up too.

[Chaplin]

Thanks guys for the info and suggestions. I'm going to try playing with it some more tonight and will post my results.

[rdorman]

Be sure to pull it and make sure the relationship I talked about above is correct! I tuned in circles for a long time until I did that. Once done, 90% of my issues went away. I was shocked that it was that important.
Rick

[Chaplin]

Alright, first I must say that people obviously think I'm nuts. Drove around tonight with gloves, hat and hooded sweatshirt (40 degrees outside) clutching a flashlight under my chin so I could read the vacuum gauge that I hooked up and routed through the firewall.

Here's what I did tonight and the results.

Changed to pv from a 2.5 to a 3.5
Changed main jets from 72s to 70s
then adjusted the idle and took a drive.
Vacuum at idle was again around 5. Car idled well and fumes were much better. Cruising vacuum was about 14 or 15.

When I stepped on the pedal, vacuum would fall to about 3.5.
However, now when cruising in 2nd or 3rd at 2500 or so and stepping on the pedal, engine would hesitate and miss badly for a few seconds - I even got one backfire through the carb

I then came back in and changed the position of the accelerator pump cam from the #1 hole to the #2 hole, took it out for another drive and still had the hesitation/miss.

Brought it back in and changed the spring in the secondary from the standard spring to the lighest spring (short yellow) and took it for a drive. Again, there was no bdifference and the hesitation/miss was still there went stepping on the pedal.

I'm thinking that I should bump the pv from a 3.5 to a 4.5 or 5 and that I should increase the discharge nozzle from a 31 to a 34 or 35 (I also planned on doing that tonight, but bought a 31 thinking that it had a 28 in it, but it already had a 31 )

Your thoughts?

Thanks

ps
Rick, I checked the things you mentioned and I think I am in good shape there.

[rdorman]

Full throttle you had 3.5 inches of vacuum? That generally indicates to small of a carb. But perhaps the vacuum secondary is playing into this. Was that reading at full throttle max rpm or what? Do go to a larger squirter (stick with the plain secondary spring while you are doing this). I would go up a bunch on the squirter size, say to a 40 for a start. Also get the cam and try the largest volume cam in the set. Be sure to adjust the squirter after this is done. Don't worry about the .015" additional travel at WOT crud. Tighten down the spring until there is a gap and then back it off until you contact the arm. If your vacuum readings are 3.5 WOT and 5 at idle, you have an issue with the power valve. I am not sure how to skin that one.

Did the car accelorate strongly once it did catch? Change one thing at a time. It may be slow but it will pay off in the long run. It does sound as though the jet size down was the wrong direction.

Tell me this, at idle do you have vaccuum at the ported vacuum port. That is the vaccuum port near the top of the main metering body.

Rick

[Chaplin]

Rick-
I never made it to full throttle. It would drop to about 3.5 when I would put the throttle about half way down- rpm was around 2800 or 3000. If I rolled on the throttle, it would pull hard, but if I stepped on it, it would hesitate/miss for a while and eventually smooth out and pull hard. This was the same with the standard spring in the secondary or the small yellow spring.

I'm haven't measured the vacuum at the port on the metering block. I'll have to check that tonight.

Incidently, I had the same problem with the hesitation/miss with the 72 jets as I do with the 70s. The only difference is my eyes aren't buring as much with the 70s