Sounds like the same thing I went through with my ol ' 360
It's almost like if there was a half way between the settings you just made would be the sweet spot , performance and air fuel ratio ....

 

Yep, that's exactly what I'm thinking. Am reading this about tuning a 1406 as if it were a 1405 with the hope of finding some 1/2 step. And, will probably call Edelbrock to see what they say.

I can run all the calculations of jet area minus rod area to look at it that way, but it isn't as straightforward as that. There's the surface or skin effect where fuel close to the surface of the jet/rod doesn't move at the same speed that fuel in the wide open moves. So, just doing the math doesn't tell the tale. In fact, if you go look at Holley jets you'll find several in a row in the chart that have the same diameter of opening, but if you look closely they have a different approach angle and that causes them to flow differently.

So, I will probably wind up calling to see what the pro's say.

 

I've done a bit of calculating on jet & rod areas and I'm confused and I'd like some help getting sorted out. The first attachment is a page from Edelbrock's Performer carb manual which shows the various options of primary jets and metering rods available, as represented by #'s. It really isn't as difficult as it first seems, with movement up the vertical axis representing richer in cruise mode and going down being leaner in cruise. (Yes, left and right represent lean/rich in the power mode, but let's stick to cruise for the moment.)

Notice that the #'s 1 through 5 are right on the axis, which means that they represent the same air/fuel ratio when the carb is in the cruise mode. And, #6 is below the axis at what I would guess to be the 1.5% lean point.

Now turn your attention to the 2nd attachment, which is the results of a bit of spreadsheeting I've done. The #'s in the first column are the same as in the first attachment, meaning the page from Edelbrock's manual, and represent the various combinations. And, the info on jet and rod diameters is taken directly from their manual as well. A teeny bit of calculation gives the area for the jet and the area for the rod, and then I subtracted the rod area from that of the jet to get the area of the "donut" that is left for fuel to flow through. And in the column marked Area % Change I simply subtracted one from the other and divided.

Voila! But wait, there's more! Edelbrock says #2 & #4 are the same as stock when #2 is actually 3.7% richer and #4 is 3.5% leaner. I know about the skin effect, and lead-in angles, but surely that can't account for a 7.2% swing.

What am I doing wrong? I do plan to call Edelbrock, but can't do that until Friday as I'm headed to KS again tomorrow. In the interim I'd like your help getting my head around what is I'm doing wrong.

And, btw, I could go with #4 and be 1/2 as lean as I am now at #8, which might prove whether this theory works or not. But, I'd be 2 stages or 8% lean on power for the primaries, and I like where they are running now, which is 12.5:1.

 

Gary, I would start by just going to a rod that is the same power diameter, but next size larger (leaner) and see what your A/F meter shows. Then see if the truck drives differently.

 

Bill - The problem appears to be the limited # of rods E'brock is supplying. The stock jetting uses .098 jet and a .075 x .047 rod. But, there aren't any rods available from them that are larger than .075. So, that means I have to change the main jet and start over on the rod. I'm now running a .095 jet and a .073 rod, but as said find that a bit too lean, although maybe acceptable. However, the next step smaller in rod is a .070 and that takes the overall mix richer than stock.

I've looked through Edelbrock's site as well as Jegs and cannot find a rod larger than .075. Do you have rods left from Carter that might help? IIRC they used to have hundreds of rod combinations.

Also, how much can I affect the mix with fuel/float level?

And, do you have any experience with modifying rods, like turning them on a lathe? I would assume a very smooth surface is needed and that is hard to get on a lathe.

 

Gary, if I do they are buried somewhere. I think I had one of the old Carter strip kits.

 

It would depend on what rods are in there. I have an Edelbrock strip kit specific to tuning the 1406 and it has the rods and jets suggested in that chart. I'll see what is available on eBay or elsewhere as maybe someone has the old Carter stuff.

 

I just saw a bunch of Carter strip kits and such in the Summit catalog. Also apparently the 1405 has a different strip kit than the 1406.

 

Yes, all of that is true. But, there are only 30 rods being sold by Edelbrock, none of which are quite what I need. I have found a few NOS Carter rods on eBay that are different sized than Edelbrock supplies and am checking to see if any if those will work. To this point I've found one that is just the right size in cruise, but the power end of the rod is .010" too big. I'm wondering if I can take that off on the lathe. Or, if I can saw rods apart and solder them back together to get the combo I want.

 

Edelbrock Performer Series Carburetor Calibration Kits 1479 - SummitRacing.com

See if you can blow up the details for this 1405 kit. I cant read it very well.

 

Sorry, I didn't explain very well. Edelbrock only makes 30 different metering rods. They are available two ways - either in individual pairs or in tuning kits. The tuning kits are specific to a carb, like the 1406 or the 1405, because they know what jets and rods are in the carb from the box, so know which rods you might need. But, in any event there are only 30 rods available, regardless of whether you buy individually or in kits.

Unfortunately, none of those 30 rods are what I need. So, I will either have to find a different sized rod from someone else, and there are almost no other manufacturers, or modify a rod to fit my needs. Or, live with what I have in there now.

I had planned to call tech support tomorrow, but a kid at church needs some automotive help so I may not get to call until next week. However, I doubt they have a magic bullet, so I'm not holding my breath. But, maybe if I set the float level high I can change the AFR enough to make what I have livable.

 

Last night I put together a spreadsheet that works out all the metering areas of all of the combinations of relevant jets (three: .092; .095; & .098") and the 30 possible rods. Turns out that there is one jet/rod combo that would give about the 4% leaner than stock AFR I'm looking for in cruise mode instead of the 7.5% I have which is a bit too lean. But, the power step on that rod is too big by .010", so it would be too lean.

Today I had a chance to call Edelbrock support to see if I'd missed something. Kevin confirmed that there really isn't a jet and rod combo half way between stock and where I am on cruise but preserves the current power AFR. I asked about raising the float level to enrichen the mix and he said I could go up another 1/16" w/o running into flooding, although beyond that I might have problems. However, he doesn't know how much help that would give. And it would also change the power AFR as well.

I also asked if anyone had asked about removing some material on the lathe or cutting some rods apart and soldering the bits back together to make an odd sized one. He said that some have gone there, but he doesn't know the results.

So, I'm not sure what the next step is, assuming I decide that what I have is too lean. Have I missed something?

 

Somewhere in the US, some elder gentleman with a small farm shop has run into this same issue, and has come up with the perfect way of solving it.

You just have to find him and pick his brain.

 

Is there anyone near you doing precision grinding, Gary.
To turn them down in a lathe & sand/polish is doable, at a pinch, but the results wouldn't be ideal.

 

Shaun - Why does he have to be in the US? How about in New Zealand?


Ken - I don't know of anyone doing precision grinding, but I will check. What about holding one piece in the headstock and the other in the tailstock and soldering them together? Take the body of the correct size and the taper and tip off another?

Or, what about using my Dremel tool post grinder to gently take that .010" off?