I finally had some time for automotive work and I installed my AFR gauge that has been sitting on a shelf for 6+ months. My black plugs (and sad mileage) were telling me that my jets were too big. The 1848 comes oe with 57 primary jets. Because of my experience with Autolite 4100's, I knew that 465 cfm model on a 289 came with 48 jets. So, tried 49 and that was too lean, hitting 17-1 at 35 mph. I switched to 51's and got the same result.

Tomorrow I'll get 53's and try them.

I'm really surprised with the QF secondary tuning pod. It actually hits the choke housing and had to be modified. Also, why did they not incorporate a three screw, quick change top? If I created the world ....

 

About the qf pod. Did you have the Holley secondary guick change kit?

 

No, I do not. That is what I mean when I say that QF should have incorporated that quick change style top into their design. With the QF style pod the owner still has dial in the secondary by finding the proper spring, which means removing the choke and the pod each time. Once you find the right spring then you are able to fine tune the secondary opening by turning the QF screw. The screw is nothing more than a carb mix screw into the vacuum passage.

I guess the way to go would be use the Holley quick change top on the QF pod until the correct spring is found, then install the QF tunable top.

 

I have the Holley installed. I like it but ordered the qf pod 3 days ago because I don't really like any one spring. I either desired the extra tuneability or can't leave well enough alone. I assumed it was a quick change. I'm optimistically hopeful that the Holley cap fits the qf pod otherwise it'll be like taking two steps back to advance one. Also hoping that it will clear the choke on my 390.
I'll let you know how it works out.
Glad I ordered extra cork gaskets.

 

As for the choke, I've never had the best of luck with Holley chokes. I think that's why a lot use the term "typical cold blooded Holley". Mine won't even jump up to the 1700 I have the high cam set to until the engine is warm. Lot of good it does me then.
I just shrug my shoulders and ignore it. There's probably a way to really get it working just right, but I haven't figured it out.

Glad to hear you got the AFR put in. That'll really help out in figuring out what's going on.
I wouldn't think that the stock 57s would make your plugs black. I run the 57s in mine. Jets are usually matched how the carb flows air through it, not necessarily its cfm.
Generally, if you have to go more than 3 jet changes in any direction from stock, your carb is either too big or too small.
Are you sure you don't have a blown power valve or something that's dumping fuel unnecessarily?

 

You're probably right. I just thought I'd try to jet it as a 4100, but the AFR proved--after lightening my wallet with new jets--that the 57's are correct.

Certainly I could have a blown pv. I don't know how to tell. It seems to open and close with my finger on it. I thought that my reading of 12.8 ish @ idle and upper 14's @ 55mph meant things were fine.

What are the symptoms of a blown PV? poor mileage ...? I just put in 12 gallons and will give it an evaluation. ( I may adopt the Mexican postman technique for calculating gallons used. There is an old story in Mexico of the post man who thought it too much work to actually open the mail boxes to see if there was outgoing mail. So, he instead dropped pebbles in and thought he could tell by the sound they made hitting the bottom of the mailbox whether or not there were letter waiting to be picked up.)

QF CAP: If you put the holley quick change cap on a QF pod you delete the adjustable mechanism of the pod. The trick is to find the spring that works best using the Holley quick change top, then switch to the QF pod or top to fine tune that spring.

 

It's usually a ruptured diaphragm inside the PV, so it'll work as normal, but gas will leak through even when it's cold.
Probably don't though, it was just an example. Symptoms are very noticeable (difficult to start, super rough idle, low engine vac, and you can usually see black exhaust at the tailpipe). Poor mileage would definitely ensue if you drove it around like that.

So you have black plugs, but a healthy AFR? That doesn't seem to add up.


I can see how that QF cap would be useful if you wanted to fine tune when the secondaries came in to perfection. But seeing as how when I'm in the ballpark and I can't really tell the difference between two springs that are close to each other, I'd probably never use it. It'd be nice if it replaced the springs altogether though.

 

I have to say, I have really enjoyed the factory Holley manual choke that came on my 570. Fully adjustable...of course cable operated..

 

I can see how a cable operated choke would be nice for just that reason. Forget trying to get it all adjusted. Just do it yourself.

Knowing me though, I'd be constantly forgetting to open it up after the engine warms and drive around with a closed choke all the time.

 

In just a matter of a short time, you would develop a routine where you open the choke in an appropriate timeframe.

 

I noticed that I lacked fuel when the secondaries came open, so I've ordered the secondary block from Allstate Carbs, with the longer tube and bolts.

I also ordered 67 jets to begin with. I know the Summit Carb I had had 67 in the secondaries and that seemed to supply enough fuel.

 

That's something I had to do with mine. The secondaries just didn't seem rich enough, so I added an adjustable secondary metering block and upped the jet size by 2. Seemed to do the trick.

I also would still really like to get an adjustable metering block for the primary side. Changing jets doesn't alter the cruise AFR, and it seems to continually stay around high 13s, low 14s. Just a tad on the rich side, and I think it needs adjustable idle feed restrictions to change that.

 

AB--I'm laughing b/c we're both trying to make what the QF carb gives you from the start. I'm thinking it may be better for me to sell my carb for $200 on ebay, and spend the extra for the QF 450. That would cost me, iirc, about $130 out of pocket?

 

You know, I've been thinking the same thing, K.
Along with the adjustable metering block (which is about $65) I had plans to drill out the air bleeds to make those screw-in adjustable too. This was all before the QF-450 was released. How much am I going to spend to update a 50 year old carb to make it behave just like the brand new QF?

The 465cfm is an awesome carb. It's the best one I've ever had on this engine. But it simply lacks the more fine-toothed tuning that I want. I'd probably be just fine with it if I left it alone, but I just can't seem to do that.

 

It also looks like there are a few more 450 cfm offerings from them now:

Black Diamond Carburetor, 450 CFM

HR-450 Hot Rod Series Carburetor



I'm kind of digging the Black Diamond one myself...