Where do I start with tuning this Holley?

woodsnake · Aug 21, 2010

My experience, both on the internet and in real life, is that MOST carburetor problems are actually ignition problems in disguise. I just went through this with a buddy of mine on his 440. We put a 750 VS Holley on that I had gone through. He had issues with a stumble on take off that were very intermittent. So, after like 5 weeks of trying to disprove the Holley, he replaced two ignition components, and now it runs like it should. I can't think of the name of the parts he replaced, it was normal MOPAR ignition stuff.

So the point beind that story is, what shape is your distributor in? Are you running an MSD box, or what?

68stang351 · Aug 21, 2010

woodsnake said:
My experience, both on the internet and in real life, is that MOST carburetor problems are actually ignition problems in disguise. I just went through this with a buddy of mine on his 440. We put a 750 VS Holley on that I had gone through. He had issues with a stumble on take off that were very intermittent. So, after like 5 weeks of trying to disprove the Holley, he replaced two ignition components, and now it runs like it should. I can't think of the name of the parts he replaced, it was normal MOPAR ignition stuff.

So the point beind that story is, what shape is your distributor in? Are you running an MSD box, or what?

Mallory Unilite with a Crane HI6 box. I never had any problems until the carb swap. Doesn't seem very likely that an ignition problem would start at the exact same time I swapped a carb.

woodsnake · Aug 21, 2010

Have you made any adjustments to the timing since you've changed the fuel curve from the previous carb?
Maybe another degree of advance? Have you tried the old school diagnostic tuning tool that can't be beat for a carbed car The vacuum gauge?
I don't know if a wide band will really get you where you need to be, or rather they are worth the money. They are great for a fuel injected engine, where you can can change the events via the computer for the car. For cars that are still using a carb, it's tough to beat a vacuum gauge.

68stang351 · Aug 21, 2010

woodsnake said:
Have you made any adjustments to the timing since you've changed the fuel curve from the previous carb?
Maybe another degree of advance? Have you tried the old school diagnostic tuning tool that can't be beat for a carbed car The vacuum gauge?
I don't know if a wide band will really get you where you need to be, or rather they are worth the money. They are great for a fuel injected engine, where you can can change the events via the computer for the car. For cars that are still using a carb, it's tough to beat a vacuum gauge.

I used a vacuum gauge when I was adjusting idle mixture, and also to help me choose a power valve. I haven't used it for driving down the road yet.

I think I'm going to buy a long vacuum hose and run it through the firewall to my vacuum pump/gauge and drive around with it and see what it's doing when my car does that. At idle, it's kind of hard to get a good reading, it flutters between 5-8, I assume because of my cam. When I open the throttle it flies up very smoothly.

As far as timing I haven't messed with it since the carb swap. Initial is around 17-18, I'm kind of scared to go any farther but I guess it's okay as long as it doesn't ping. The total is 36. Maybe I should change the advance curve in my distributor? But would the advance need to come in sooner or later?

I really appreciate all the help and the time you guys are spending to help me.

68stang351 · Aug 22, 2010

Driving around it seemed to stay around 15 for just normal driving. When it stumbles it drops down to 0, then returns up to around 15 or whatever it was before the stumble.

It's still fluttery though, I wonder if I have a vacuum leak.

brianj5600 · Aug 22, 2010

I think that a wideband that can datalog is extremely helpfull when tuning a carb. I can see if it is rich or lean when stabbing the throttle. I was able to determine that the pump shot lasted longer than it needed. W/O trial and error I knew I needed less lift on the cam. I could also see that the high speed air bleeds were too big. It would lean out as rpm went up. At the strip it was not responding to jet changes. Going bigger helped parts of the rev range and hurt others, same for smaller jets. Going smaller on the hsab gave me a much flatter fuel curve and I was able to get .2 and 2 mph in the 1/8. You can not read that on spark plugs. It also tells me my A/F ratio in real time all the time. There is no way to tune a carb to a high level w/o one IMO. You can get good drivability, but with out a wide band you will not know what is going on all the time. The best money I have spent on my car to date.

doogie67 · Aug 22, 2010

I second what Brianj5600 said. It is also the best money I every spent. If you are cruising at a 11:1 AFR and you lean it out to 14.5:1 you will get 30% better fuel economy. An example of one thing of many a wide band can do.

woodsnake · Aug 23, 2010

I'll have to learn to rethink my strategery on that. For a street driven car, I wouldn't think its worth the cost, but I guess as they become more popular and less expensive, I should add one to my tool box.

68stang351 · Aug 23, 2010

Here's a vid of what it's doing.

stutter video by LtBullitt - Photobucket

You probably have to turn the sound up, and it's a little crackly (it was taken with a regular camera), but you can still hear what happens.

woodsnake · Aug 23, 2010

I can't see it at work, stupid USG computers....

68stang351 · Aug 6, 2011

I hate to resurrect threads, but I've just been living with this problem for the last year.

I have had the car on a chassis dyno. At WOT, it was just a hair rich. When he was going through the gears to get to 4th, it was way way lean.

Could I simply need bigger jets on the primary?

PoppyMod · Aug 6, 2011

68stang351 said:
I hate to resurrect threads, but I've just been living with this problem for the last year.

I have had the car on a chassis dyno. At WOT, it was just a hair rich. When he was going through the gears to get to 4th, it was way way lean.

Could I simply need bigger jets on the primary?

Hi,
When you state a "hair rich", what is the AFR #? When you state, "way way lean", what is the AFR#? Need specifics.
My engine makes it's max RWHP at WOT (5900) with an AFR of low 13s. Accelerating through the gears, there shouldn't be more than about a one point difference. That is, if the pull starts around 25-2800 or so. Typically, when first punched, there is a momentary lean 14+, then it should settle back to fatter AFR of somewhere in the high 12s low 13s until your red line.
This has been my experience when tuning for best WOT performance. My idle is in the low-mid 14s, but, under throttle, it's about 13.1-3.
It's a matter of swapping secondary jets until you find that "sweet spot".
Good luck!

68stang351 · Aug 7, 2011

PoppyMod said:
Hi,
When you state a "hair rich", what is the AFR #? When you state, "way way lean", what is the AFR#? Need specifics.
My engine makes it's max RWHP at WOT (5900) with an AFR of low 13s. Accelerating through the gears, there shouldn't be more than about a one point difference. That is, if the pull starts around 25-2800 or so. Typically, when first punched, there is a momentary lean 14+, then it should settle back to fatter AFR of somewhere in the high 12s low 13s until your red line.
This has been my experience when tuning for best WOT performance. My idle is in the low-mid 14s, but, under throttle, it's about 13.1-3.
It's a matter of swapping secondary jets until you find that "sweet spot".
Good luck!

At WOT it dropped down to about 10:1 for a a few rpms then levels out at right about 12:1.
As for it being lean, I saw it go up to around 17:1.

I'm going to do some more cleaning to make sure all the passages are open and put some richer primary jets in it today.

PoppyMod · Aug 7, 2011

68stang351 said:
At WOT it dropped down to about 10:1 for a a few rpms then levels out at right about 12:1.
As for it being lean, I saw it go up to around 17:1.

I'm going to do some more cleaning to make sure all the passages are open and put some richer primary jets in it today.

Sounds like a plan. What size carb? Might want to lean out those secondaries a bit. Maybe the pump shot is too lean and not the primaries on the initial kick?
Good Luck!

68stang351 · Aug 7, 2011

It's a 780. I know it may be considered by some to be too big, but it runs better than the Edelbrock 600 I took off of it.

I thought about putting 74's all the way around, or even switching the primaries and secondary jets to have 76 in the primary and 72 in the secondaries.

I just don't know how much of an increase I need. I may get an O2 sensor and meter.

Thanks for the help.

PoppyMod · Aug 7, 2011

68stang351 said:
It's a 780. I know it may be considered by some to be too big, but it runs better than the Edelbrock 600 I took off of it.

I thought about putting 74's all the way around, or even switching the primaries and secondary jets to have 76 in the primary and 72 in the secondaries.

I just don't know how much of an increase I need. I may get an O2 sensor and meter.

Thanks for the help.

...What is the rest of your build that supports a "780".
Just wondering?

68stang351 · Aug 8, 2011

PoppyMod said:
...What is the rest of your build that supports a "780".
Just wondering?

351w, Trick Flow Twisted Wedge heads, Comp XE284 cam, Performer RPM intake.
I know it's probably a little big, but it was given to me and it easily outperforms the Edelbrock 600 that was on it. All I had to spend on it was the rebuild kit and the tuning stuff I bought that I can use on just about any Holley I'll ever have.

PoppyMod · Aug 8, 2011

68stang351 said:
351w, Trick Flow Twisted Wedge heads, Comp XE284 cam, Performer RPM intake.
I know it's probably a little big, but it was given to me and it easily outperforms the Edelbrock 600 that was on it. All I had to spend on it was the rebuild kit and the tuning stuff I bought that I can use on just about any Holley I'll ever have.

Hi,
First you got some good stuff going, it's shame to waste it's effectiveness.
I think the first thing you should do is rent or purchase an engine vac gauge and get the basic readings and tune the carb. Note all of your engine's baseline data. Include a graph of your dizzy's advance rate in 500 R increments to approximately 3K.
Next, definitely add the 02 sensor(s) bung(s) in the collector, adding to both sides while you're at it. After which, I would seriously consider scheduling a few sessions on a chassis dyno. You will learn a lot about what you're AFR is doing from about 2500 to 6500 Rs. It is well worth the $150, or so $s. If no convenient Dyno shops around, then purchase a "quality" wide band AFR testing kit and have at it. The data logging feature will allow you to get on the road readings that can be reviewed on a laptop later. But, most good kits will cost about $300. The other thought, (less expensive) is Innovate makes a dash mounted wide-band gauge that connects to a sensor bung, that will provide "real-time" AFR readings.
I have an Innovate set-up that I started using prior to doing attending 3-4 Dyno sessions. The sessions will show where you're AFR is lean or fat, or, if the carb is just too big to jet down. It would be good to get a 14"ish AFR idle reading with with a fairly flat line 12-9-13-3 AFR, or s,o at WOT or 6000-6500, what ever your engine's red-line.

Another system to fine tune is your dizzy curve and the vac unit. If this is a street warrior, there is no shame in running a dizzy vac. However, the engine may "like" one port over the other.

My engine responds best to full vac. I 'm running 16 deg initial, about 4 deg dizzy vac, with "all in" at 3100 Rs.
As a comparison, my 333, running 170 TWs (w/little port work), Performer RPM, 680 custom tuned Holly XE, TRY-Ys, CI hydraulic roller, custom curved dizzy powered by a Jacobs sparkie box. My rig was dynoed at 392 RWHP at 5900 with 400 RWTQ at 4400.
I fined tuned all of the major players to insure I left no, or very little, HP/TQ on the table. In the end, maybe I did, as I forgot to remove the K&N air cleaner before making the runs.
I hope some of this helps!

Good Luck!

68stang351 · Aug 8, 2011

PoppyMod said:
Hi,
First you got some good stuff going, it's shame to waste it's effectiveness.
I think the first thing you should do is rent or purchase an engine vac gauge and get the basic readings and tune the carb. Note all of your engine's baseline data. Include a graph of your dizzy's advance rate in 500 R increments to approximately 3K.
Next, definitely add the 02 sensor(s) bung(s) in the collector, adding to both sides while you're at it. After which, I would seriously consider scheduling a few sessions on a chassis dyno. You will learn a lot about what you're AFR is doing from about 2500 to 6500 Rs. It is well worth the $150, or so $s. If no convenient Dyno shops around, then purchase a "quality" wide band AFR testing kit and have at it. The data logging feature will allow you to get on the road readings that can be reviewed on a laptop later. But, most good kits will cost about $300. The other thought, (less expensive) is Innovate makes a dash mounted wide-band gauge that connects to a sensor bung, that will provide "real-time" AFR readings.
I have an Innovate set-up that I started using prior to doing attending 3-4 Dyno sessions. The sessions will show where you're AFR is lean or fat, or, if the carb is just too big to jet down. It would be good to get a 14"ish AFR idle reading with with a fairly flat line 12-9-13-3 AFR, or s,o at WOT or 6000-6500, what ever your engine's red-line.

Another system to fine tune is your dizzy curve and the vac unit. If this is a street warrior, there is no shame in running a dizzy vac. However, the engine may "like" one port over the other.

My engine responds best to full vac. I 'm running 16 deg initial, about 4 deg dizzy vac, with "all in" at 3100 Rs.
As a comparison, my 333, running 170 TWs (w/little port work), Performer RPM, 680 custom tuned Holly XE, TRY-Ys, CI hydraulic roller, custom curved dizzy powered by a Jacobs sparkie box. My rig was dynoed at 392 RWHP at 5900 with 400 RWTQ at 4400.
I fined tuned all of the major players to insure I left no, or very little, HP/TQ on the table. In the end, maybe I did, as I forgot to remove the K&N air cleaner before making the runs.
I hope some of this helps!

Good Luck!

I fixed the stumble by switching the jets.
I know there has to be more power left in this thing. When I had it dyno'd it only made 288 rwhp and 343 tq, though on the last run I saw that my vacuum secondaries were only opening a little over halfway. I've since put a litghter spring in it and it's better, but still no where near your numbers for your 333. It does have low compression pistons going against it though. BTW this thing falls off pretty bad at about 5500, I thought it would go a little higher than that.

I have been thinking about taking it back to that shop and letting them tune it on the dyno. But I don't know that I'm ever going to get all I can out of this carb. I would like to have a 670.

I have a Mallory Unilite distributor with mechanical advance and a Crane HI6 Fireball box. In a minute I'm going to go check out my timing. I'll post that up for you.

68stang351 · Aug 8, 2011

Initial is 18, all in is 34, I couldn't look at my tach while I was doing this, but it sounded like it was all in by around 3k rpm.

Where do I start with tuning this Holley?

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