Hi everyone. I've been doing a lot of reading about tuning Holley carbs the 'right' way and I think it's time for me to do my own. I have read the OCD Carb Tuning thread by speedtigger along with its associated threads. I'll be buying all of my equipment soon, along with a wideband. I know that the carburetor will be out of whack, and plenty rich (also from experience) so I want to set up a base calibration that I think will get me close to ballpark based on what I have read.

Here's the setup:
-Bone stock 2002 5.3
-1.75" longtubes
-LS1 performer rpm intake
-Holley 650 (stock so far) 4777-3 with Quickfuel 34-4 stock callibration metering block
-23" of vacuum at idle
-M20
-3.08 w/ 24" tire

Here's what I plan to do:
-10.5 PV to start (I think it will eventually need to be stronger)
-Moving the IFR from .033" (at the top) to .028" (at the bottom)
-Main air bleeds to .026" (they may already be close, I will check this weekend)
-Main Jets from 67 to 65
-PVCR from .055 to .057 (actual PVCR change is .0573" for constant area)
-keep stock .028 kill bleed and stock emulsion setup for now

Does this sound ok? I feel like this will get me close(r) to proper settings.
Also, when I move the IFR to the bottom of the metering block, do I need to drill into any passage first, or just tap the hole and move the restrictor?

Any opinions from someone who has experience with this type of tuning would be great.

Thanks!

 

You are not going to know until you do it. I know places like Karb King and Pro Systems keep good records of what worked for different customers and thus claim they can ship a mail order tune. BUT even the mighty pro systems carbs need tweaking to dial in the part throttle response.

Your set up is probably a good starting point, just keep good records so you can back out changes that go the wrong way.

 

drive around with a vacuum gauge so you can see it to help pick a power valve. once you get a wideband it will help a lot and you will be obsessed with it lol

 

I found that a wideband is a LOT easier than plug reading Just wish I found out earlier in life

 

Thanks. I will report back with the results. The QF metering block came with only one emulsion hole plugged (#3). I think I will be plugging #2 and #4 instead since most people seem to have best results with that setup.

Also, I'm ordering my bits from McMaster carr. If the bit has no shank diameter listed, do I assume that it's the same as the drilling size? I can't imagine finding a drill that would take a .026" bit without some type of adapter.

 

I honestly wouldn't monkey with the emulsion holes. Seems like more internet voodoo than any real tuning aid.

Buy a pin vice to hold the drill bits. Put the brass set screws in the jaws of a variable speed cordless drill and turn the screw at a slow rate. Than with lots of WD40 or the like hold the drill bit stationary and drill the hole as straight as you can.

Strongly suggest buying a set of wire drills with an indexed holder. This one is pricy but invaluable to keep the bits organized properly.


You will need larger bits as well. A good set of lettered bits works. I measure the shanks with a caliper and record that in my notes whenever I drill a hole. The twist part seems ever so slightly smaller in diameter than the shank, but consistency is what matters here. Use the same set of bits to measure the diameter of existing orifices.

 

Thanks for the heads up, maybe I'll leave them alone for now and see how it runs.

I found a micro-bit chuck on amazon for $7, so I'm gonna try that out in a drill press instead of the pin vise.

 

Go slow and easy. The slightest bit of side load and those little bits snap like no tomorrow.

Holding the bit stationary and turning the blank works quite well

I shouldn't have said the emulsion holes aren't a tuning aid. It just seems like you would need to be a really sophisticated individual to get them right. There are so many other things to tune that emulsion tubes might just get you in trouble. I would trust quick fuel and Holley before some random internet guru.

 

I'm back with an update and some info for those who haven't attempted this yet.

Here's what I suggest:
-Buy bit sizes #65 to 73 from McMaster, I felt that they were good quality
-Buy cup-point brass set screws, the cupped bottom makes drilling sooo easy
-If you have a QF metering block(and maybe even some holleys are like this) you don't need to drill anything for the lower IFR. Just tap the hole with a 6-32 tap until you bottom out, then carefully give it an extra quarter turn and you should be right about where you need to be.

-To make drilling the set screw blanks easier, I bought a micro-chuck adapter. You can get one from McMaster for about $10. The 'secret' is to tighten the chuck by hand while only allowing about 1/8" of the bit to stick out of the chuck. This allows for less off-center spin (the chuck/adaptor that I bought was a bit lower quality) You only need enough bit to break the surface of the set screw.

-Make a mounting block for the set screws. Take a piece of you favorite metal, about 1in x 1in x .5in, and drill about 3/16in into the top face, and then tap about 1/8in into it (no more). Now screw the blank in upside-down and you're ready to drill!



-Be patient and gentle. If you are careful, these bits will last you a long time. A drill press made this process pretty simple.

 

Ok, I've gotten my idle dialed in, only using two corners (in the front). I left the Jets and PVR stock, and upped the squirter to a 31 (acceleration was too lean). It's a bit better now, but the light cruise and light acceleration is too lean. I'm getting between 15.5 and 17 at around 35-45 mph (~1500-2000 rpm).

Should I make the IFR larger? The idle mixture screws are only out about 1 full turn so I figured that the IFR was good.

My thought was to enlarge the Idle bleeds a bit, I think right now they are about .070 (stock). Am I thinking in the right direction?

 

Might want to be careful with that. The restriction can be in the way back of the channel. I made that mistake early on when I was trying to use a wire in a Holley IFR.

You really need to try putting the blank in the drill chuck and holding the bit in the micro chuck/pin vice. You could have drilled all your blanks in the time it took you to make the drill jig. I used 3 different sizes of blanks and the different sized orifices so you still have some work to do.

 

The QF have no lower restriction to drill out, they utilize the top one.

It only took me about half an hour to make all the 6-32 sizes, but I do plan on making the larger 10-32 blanks for the air bleeds.

 

Emulsion holes are not voodoo. While I have never asked them directly, I have never seen any mention of witch doctors at Holley.

If you look at the carburetors Holley has been making for the last 50 years, you can see the difference between the emulsion strategies they used for OEM vs what they have used for performance aftermarket and racing vs what specialty shops and race tuners have changed that they felt were better for thier application.

What many of the sharper custom Holley builders advocate is a return to the early OEM style of emulsion calibration as a solution to tuning problems they are encountering with the newer aftermarket calibrations on street driven vehicles.

 

Of all the things you could do to tune a motor the emulsion circuits would be the absolute last thing I would touch.

 

If you are just tuning and tweaking to improve what you have, I agree completely.

 

Reducing the IAB to 62 from stock (approximately 70) helped the cruise, which is now in the high 14's/occasionaly low 15's. IFR is still at .028, but thinking about reducing it to .026 to get more adjustability out of the mixture screws, since they are very sensitive to minor tweaks. Is this a good idea?

Also, I am still only running with the two front barrels, and WOT dips down into the 11's and high 10's. As I see it, I have a few options:
-go down a couple of jet sizes, PVR will need to be resized
-go down a couple of PVR sizes
-reduce the HSAB, may cause the mains to come in too early, maybe not. They are at .033 now, I could go to .026 and work up from there
-play with emulsion, which I don't want to do
-Buy a new carb

So as of now, these are the options that I'm aware of. Will one of these changes be far superior to the others? Thanks.

 

If you have the cruise where you want it, I would try to reduce the PVCRs to see if that gets you the WOT you want. You just have to watch out that your aggressive part throttle does not get too lean.

 

I Replaced the .028 IFR with the .026 and reduced the IAB with the equivalent. Unfortunately it did not help with the idle screws at all, they are still very sensitive. I guess leaning the IFR and then strengthening the signal through the IAB will net the same mixture? It's not really a big deal since I can get the idle pretty close, but it would be nice if it were more consistent.

Stock secondary jets are .073. With a .067 jet in the front, the equivalent PVCR is a .029. Stock PVCR from quickfuel is a .055. I reduced it to a .033 to get close, and WOT goes to about 12.2 at first, and then as the rpms increase it gets down to 11.4. So I guess it's better than before, but should I still be shooting for a 12.5 WOT?