Jon's 2-barrel carb service thread

[kjc-01]

Michael,

I have a Holley 2-barrel (list number 4306, line set number 379473-C91, date code 011, metering block 5965, size 54 jets, 7.5 in Hg power valve, white cam in #1 position, see 1st and 2nd photo) in my 1970 1200D 4x4 manual trans pickup. It has a fairly stock 345 (Pertronix igniter, K&N filter, headers) motor. I believe this is the stock 2300 carb, as the truck has been in the family since new. It's been rebuilt at least a couple of times but needed more love when fuel began pouring out from under the head of the float bowl attach bolt nearest the fuel inlet. I started in with a Holley 3-396 Renew Kit I picked up a few years back (which I believe is for marine applications). During reassembly I observed a vacuum path to the power valve that was blocked by both the old and new throttle body gaskets. The path joins manifold vacuum to the volume behind the power valve through a hole cross-drilled in the throttle plate shaft (on right side of 3rd photo) that is open at full throttle. My understanding of power valves is that they are a poppet valve closed under high manifold vacuum and open when vacuum drops (like at WOT). So I took my punch set and opened up a hole in the gasket to 'activate' this pathway. The old gasket was closed in this area as well, and the truck, although driving like a 39-year old farm truck, ran fine for my purposes. So now the questions:

1. Was modifying the gasket a foolish thing to do, or can I now expect a miraculous improvement in performance under load after the accelerator pump squirt has ended? Obviously we'll know more when I fire it up.
2. Is there a more correct Holley Renew Kit (or other manufacturer) recommended for this carb? My list number does not come up in the service parts catalog.
3. I plan to reflatten or replace the worn accelerator pump arm (4th photo) and the likely worn down white cam while I'm at it. I also am planning on converting to a spring-loaded needle-and-seat (pt. no. 6-513) and vent extension to supplement the existing bowl vent screen. Is this worth it for mild wheeling?
4. Can main jet extensions be added with a side-hung float? No notched side-hung float is offered by Holley.
5. Is the 'heat shield' base gasket referred to in the forums required to shield only the float bowl, or on all sides?

[Michael Mayben]

Nice write up Jon! Great detail! And welcome to the forum!

That carb appears to be a "commercial" reman as I can see the CARB "sticker" on it. Unless you peeled that off somethin' else and stuck it on there to fool them dam smognazis down there!

But that older schnizz don't have to be smogged in your playpen anymore unless that sumbitch Auhnuld extended the exemption yesterday to make up for the busted treasure chest sitch. So pay for any smog check with a fuckin' "IOU" also, same for yore registration renewal. Pay yore property taxes with a fuckin' IOU too.

That carb was ONLY used in some '69 model 304 and 345 motors in "some" platforms! It has a weirdass "INDUCED" vacuum leak that is active ONLY at WOT...that is why that throttle shaft is drilled through! I have two of those I keep around for conversation starters!

The "fix" for that??? See that hole in the air horn right behind the choke link on the flat section??? PLUG it! I use lead shot for that kinda deal so it's easy to remove later if ya wanna.

All of the OEM-style 2300 carbs have either a blind hole in that position or a partially drilled hole that does NOT go all the way through. The 4306 is the ONLY dedicated IH p/n carb I've found though that has that circuit "active" but is useless! It's all about emissions!

I use the generic kit for the 2300, a Holley p/n 37-1543. Those are designed for the current 2300 "centerhung float" carbs but will work just fine. You MUST match the proper throttle body gasket to your original (hoping the original is correct!), do NOT use the larger one which is for a 5oocfm version with larger venturis and throttle plate diameter.

Then ya MAY have to "match" the various holes carefully, so what you did IS the proper procedure!

I think the "spring-loaded" needle seat sets are worthless, I DON'T use those in my work OR in my own off-road capable rigs! The jet extensions can only be used with the notched floats with the center hung bowl. So yes...you CAN mod a NEW 2300 (List 0-7448) with all that stuff. You "could" add a centerhung bowl set to your carb but that would be of no real value IMHO. There IS sufficient room to mount a 2V centerhung Holley on your manifold, but you CANNOT use a centerhung Holley 4V carb because the front fuel bowl is nearly an inch too long and will hit the tstat housing!

The vent extensions I make out of nylon fuel-rated tubing such as used for emissions connections. Somewhere around here you will see some I make out of nylon "coilee"-type air hose and have given away to many folks around here. Those are DEFINITELY of value (along with proper setting of the adjustable fuel level in the bowl). That perforated screen part that Holley offers is also a part that DOES work and will work on a sidehung bowl setup.

Definitely work over that accel pump arm, your drivability right now must REALLY suk! You will be astounded at how nice tip-in can bee when all that stuff is fresh!!!

Since the gasket mod ya made (great that you traced that out and now understand how the power valve system on these carbs work!) should now allow the power valve to actually function (I'd guess the power valve you have is either a 75 or 65, either works just fine), you will now experience greatly enhanced performance when manifold vacuum hits the actuation point. Before, if the PV did not actuate, the engine should have been surging somewhat, just as if it was running out of fuel.

Let's keep going until you are satisfied it's the best it can be!

[kjc-01]

Michael,

Thanks for the quick and detailed reply. I saw you are working out a stone...lemon water helps me with the small ones, whatever you can get your hands on for the big ones! After reading your reply I tore the carb back apart just to double check a few things. The sticker on the front is from the place that rebuilt it about 16 years ago (and had fuel pouring out of the vent the first time I fired it up. I don't go there anymore). I confirmed the existence of the hole in the flat next to the horn (photo #1). I then traced the path and you are right - it bleeds air to the power valve at WOT (arrow in photo #2). Hmmm...sound like the 'economizer valve' logic so they could undersize the rest of the carb for 'normal' driving. Anyway, I'll heed your advice and close it back off. Next I cleaned up the accelerator pump arm with some filework (photos #3 and #4) and cleaned out the accelerator pump needle valve that I missed the first time around, there were some whitish deposits (corrosion?) and the needle did not come out easily - I need some smaller fingers to get past the choke plate. I got nervous when I saw the bad fit of the throttle body gasket over one hole, but chased it down to find it was a blind path (arrow in photo #5). So all is reassembled and installed on the rig. Too late to fire it up now, but will try it tomorrow and report back! Tasks for the holiday weekend include replacing the white accelerator pump cam, plugging back up the 'hole o' shame', finally advancing the timing ~5 deg, and installing the vacuum gauge I've had sitting in a bag for 10 years. I will abandon plans for the spring-loaded needle/seat and jet extensions. Take care!

-Jon

[Michael Mayben]

I vaguely remember my urologist back in Tejas tellin' me about the lemon/water home remedy! Thanks for the reminder, I'll get right on that!

I kept rubbin' up against the microwave also hopin' that radar might work like lithroscopy but it don't, just cooked my liver!

Anyway, thanks again for your excellent descriptions, that is what allows all of us around here to learn this stuff and be able to share it!

Not only does the List 4306 Holley have that strange metered vacuum leak, so does another version, List 4574 that was used on some IHC apps as well.

And I have seen some of the remanned carbs that have the WRONG throttle body married to the WRONG main body...typical commercial remanner "don't care just ship it" shit.

Let's try and work through this since you are willing to look at these details!

First...nice work on the accel pump lever. ya may need to bend it to achieve a nice "adjustment" with full pump stroke, that will compensate for removal of material. That arm was as bad or worse than any other I've ever seen!

The corrosion down in the accel pump "shooter discharge check is fairly common. Indicates that moisture had been present at some point. There are at least three distinct check systems used in that carb series. One of 'em is a "ball" that is inserted first, then a short piece of what appears to be a roller bearing is dropped on top and called a "check ball weight". That carb body MUST use a check ball, the radius of the seat down the hole matches the ball!

The second type uses a "short" needle valve with the same "weight" added on top. That main body is machined for the pointed end of that check valve.

The third type is a "long" needle, that one does NOT use a weight. The short needle and "long" needle systems will interchange, but NOT with a "ball" carb body!

I also see fairly often where obviously the correct check needle was missing and someone uses a plain old float needle down the hole. When ya run in the shooter screw with the correct top and bottom seals, the screw then drives the needle into the hole/seat and they then strip the threads trying to keep the shooter from leaking (if it works at all).

Without that check system in place, the carb will siphon raw fuel right through the shooter at all times, resulting in a super-rich condition.

The throttle body gasket I see in your pic is entirely the wrong item for that carb!

That one is for a 500cfm version of the 2300, most likely an aftermarket replacement List 4412 (pic of one of those is in the 2300 sticky thread). See how the throttle bore cutouts are too large??? And the holes don't really match at all.

There are MANY throttle body gaskets used on HUNDREDS of different 2300 List carbs! That Holley carb kit number I posted fits MANY of those, there are other kit numbers for different versions. But I use that kit on most all of those carbs since it does have the parts needed IF ya can figgr out what parts to use!

My first pic shows your EXACT same List carb disassembled. The gasket that is stuck to the main body is OEM and I consider that one to be the guide I use for all these carbs! So compare this pic with your stuff and you will easily ID the differences! The arrow inked on the throttle body shows the position of the auxiliary port we're talking here that is drilled through the throttle shaft. Best practice is to plug that hole also if ya got the carb torn down.

[Michael Mayben]

This shot shows the correct gasket mounted on the throttle body so ya can see WHAT holes are needed. Also you see on the right hand side of the gasket that it is wider than the gasket you have. That is a distinctive portion of the gasket that must be considered.

[Michael Mayben]

Here's the gasket by itself against a white background.

You can see the "straight edge portion on the upper right side. That covers completely that "channel" that leads to the hole in the throttle shaft.

[Michael Mayben]

This shot shows a comparison, with the correct gasket in the middle.

The lower gasket is similar to the one you have used and is for a 500cfm carb.

The upper gasket is one that is included in the Holley kit I mentioned. That gasket is the one that I use on these carbs AFTER blocking both the throttle plate hole and the hole in the main body air horn. The part number beside it is for a package of ten gaskets that are available through a Holley distributor in bulk.

Sometimes items such as that may also be ordered through Holley Technical Service. And there is an old time speed shop in Salem, OR with a TREMENDOUS selection of individual gaskets hanging very neatly on the wall pegboard. Steve Tepper is the owner, does bizz as Performance Racing Equipment, 503.371.8622. He's helped me a few times with proper p/n ID of some of this stuff as his collection of information goes back 50+ years. Steve has more Holley stuff on hand than Holley Performance has in Bowling Green!

You can see that it does NOT completely cover that passage milled into the throttle body. But if the hole is plugged it will be OK. I also use that gasket on other versions of these same carb series, since the channel on those is inactive due to the throttle shaft not being drilled, it doesn't matter.

On many occasions, I simply cut the gasket I need out of some Interface Solutions paper that is the same exact formula as the gaskets used in the Holley kits. Those are NOT the "blue" neoprene impregnated gaskets, those are Holley proprietary that replaced the older "brown" gaskets that were treated with a pressure sensitive coating and stick so stubbornly.

What else can we help ya with, let's keep going until it's perfect!

[kjc-01]

Michael,

Glad the lemon water suggestion was helpful. Looks like I really messed up the throttle body gasket selection. So is this a 350 cfm carb? I hope I have the 'long needle' style check valve, as there was no roller bearing weight on top of the needle. Can you tell me what the actual lengths of the two different needles are, so I can measure to see if I'm missing the weight or (hopefully) have the short one?

I picked up a 37-1543 kit, a set of accelerator pump cams, and a set of carb mounting studs this morning at Santa Ana Speed Center. If I want to use the throttle body gasket in that kit instead of ordering the 108-74, you mentioned using lead shot to block the air leak passages in the throttle body and the main body. Is that just a matter of finding slightly oversize lead shot and jamming it in the higher pressure side? I can see the conversation at the gun shop "I'd like two pieces of no. 6 shot, please.". Will a dab of silicone work if they laugh me out of the place?

-Jon

[Michael Mayben]

Your particular carb is actually an "OEM" version of the 2300 series. There were MANY different versions produced, the most "significant" were the really special units used on the three dueces setup for the Ford 406 musclemotors! The "D" shape to the air horns allowed a compact fit for the air cleaner and the vacuum actuated progressive throttle linkage was pretty unique also! Same for the lack of idle circuits, etc.

So they actual "cfm" for yours is rated at 275>285cfm. And 2V carbs are "rated" under an entirely different pressure drop standard as compared to a 4V carb. So ya cannot directly compare the 2V and 4v mixers, even though we say that the 2300 series is "one half" of a 41XX series modular. And keep in mind, this carb was introduced circa 1953 and is STILL going strong today as the primary carb allowed in MANY forms of circle track competition!

Holley has re-introduced many of their old OEM carbs for the muscle car stuff this year...EXACT same carbs in zinc. So there IS a market for this Holley stuff, but that is driven mostly by the Ford and GM enthusiasts. But I don't believe they have brought back any of the OEM 2300 carbs yet, the current List 7448 and 4412 mixers fill the circle track market along with their "Keith Dorton" version of a "built" 2V carb. The 7448 carb is the PERFECT replacement for what you are working with though, especially with the electric choke conversion.

The "Holley Performance Products" company today (and since around 1991) is NOT the same company as the old Holley Corp. which was a part of Colt Industries when they went tits up in 1988 or so. Borg Warner bought the "old" Holley OEM business at the bankruptcy fire sale.

I digress for the historical aspect, that DOES affect the parts supply we're discussing right now! Santa Ana Speed??? I've darkened their doors back in time...I lived on the sand at Huntington Beach for longer than I care to remember! Are you hooked up with the Scouts West kidz???? A few of their members are in that area also. And ya GOTTA connect with our other moderator here, Robert Kenney...the "Asphalt Gigolo", he's up in LaVerne and Duarte!

Here's a pic of the accel pump checks. Yours "should" have the single long needle, it measures exactly 1/2".

The ball on the left is a part normally found IN the carb kits, that same ball is also "sometimes" used in other locations. It would have used the cylindrical weight on top, but an second ball can be used for that purpose also.

The center pic is a "steel" long needle, some are brass, doesn't matter. IF ya cut that long needle in half, that would be a "short needle! And...it would have the cylindrical section on top...so in essence it's EXACTLY the same mass overall and length as the single long needle. The main thing is, ya can't interchange a ball carb body with a needle check and visa-versa.

The far right shows a typical "PO fuckup"!!!! Someone put a BALL in the hole first, then installed a LONG needle and cranked down on the shooter screw! That is because the instructions show BOTH systems but don't say to use one or the other as "found"!!!! So that drove the ball into the tip of the check...as you can imagine...THIS carb had NO accel pump shot...but the owner claimed it was "freshly rebuilt" and that "ALL Holleys are junk"!!! Ya see that repeated sometimes around here...but what other carburetor is STILL the most popular mixer ever designed/sold and is STILL in production after nearly 60 years!

That kit you picked up will have that EXACT gasket in it I showed in the pic! No need to buy anything else! And that kit has at least two other gaskets (maybe three) that you will NOT use! It's a very flexible application but you DO need either experience in doing this stuff or some guidance, or YOU will be a "PO fuckup" too!

I here ya about the lead shot deal and a gun shop, they never sold me shot by the piece! But I buy lead split shot (not that fuckin' bismuth shit) at the tackle shop (we're flyfishers and use tiny amounts of splitshot on nymphs sometimes). Or ya can use the ORIGINAL JBWeld. That shit works immersed in even E10!! I use it for repairing the fuel bowls that ALL leak on the Quadrajet and Thermoquad carbs.

I know ya haven't been here long...but those that have KNOW how I abhor silliclone/RTV. That shit cannot be used anywhere around a carburetor! RTV is GREAT for our business, anytime someone uses it, it results in a blowed up carb so we get to fix it! Some of our members know that I got an RTV detector set up at the end of the driveway, it fires off if ANYTHING with RTV on/in it attempts to come on the premises! Then the Mossberg Cruiser automatically racks and that's a signal to park out on the highway!

[kjc-01]

Michael,

The 37-1543 kit has been installed and the throttle body gasket fits much better (photo below). When I compare it to your 108-74 photo I see the passage for the air bleed circuit is in your gasket but not in mine! The 37-1543 appears to be an exact match for the one that was removed at the beginning of this tear-down, so the previous rebuild was correct. The accelerator pump cam has been replaced as well, with much less wear evident than expected after seeing how much material it took off the pump lever arm. Is there a renew kit with the correct throttle body gasket for the next full rebuild, as the fast kit is a bit lean on the other gaskets.

There were 4 nylon washers in the fast kit that looked like a perfect fit for the float bowl bolt gaskets. Is that what they were for? My accelerator pump circuit check valve needle was the 1/2 inch kind and the tip is in good shape, so no lost parts there. I will pick up some small split shot from the local outdoors store, as my saltwater lead won't quite fit. I plan on shoving one in the main body passage air bleed only, as the other half of that weird power valve circuit below the throttle body gasket to the power valve vacuum side is sealed off by the gasket - since there is no hole there. The upper half appears to let unfiltered air into the interior of the air cleaner and should be sealed. Thanks for sharing all your hard-earned carburetor wisdom with me!

-Jon

[Michael Mayben]

I'm CONSTANTLY looking for "better" versions of these kits Jon! For many years Holley supplied CORRECT kits for most any OEM Holley carb, but that program has been hugely scaled back in recent years simply because the market for such is just not there!

Those "blister pack" kits we see are based upon the fitzall approach of service parts consolidation which has been overtaking the industry in the last several years.

I need to take some downtime and simply sit down with the Holley "big book" and go through MANY List numbers and analyze which gaskets are correct for which application. Then I can discuss this with Holley Tech using common language...part numbers...and see what we can do. I do have some Holley-supplied Bills of Material they have released to me in the past that is a real help. Keep in mind, we're small time operators compared to many sources, but Holley Tech always come through for me (that was NOT the case years ago, they have changed and now recognize customer service for what it is!).

If you go to the current Holley website, you can download the full catalog now which contains a ton of "tech". And that catalog changes often so I save all versions for past years. It also has listings for all current kits available.

Many of Holley's regional warehouse distributors have older inventory and may include many kits that are no longer being manufactured. The Standard Hygrade stuff is also a viable alternative if you can get a countermonkey to look up the right stuff by correct vehicle application, their PAPER dbase catalog is an outstanding resource. I'm using the Hygrade stuff with great success for Thermoquad and Quadrajet mixers, but Wells is my goto for most kits. Not everyone has access to a Wells WD though, they are the primary source for most of the actual parts that you find in ANY carb kit (even the stuff sourced from Holley!).

And this next week, we'll be looking at some stuff from Light Line that may be on the horizon regarding carburetor components!

The CORRECT Holleysource kit that has been available in the past which is dedicated for that carb List is: 83R-3073-S. I'm sure there are some of those available SOMEWHERE in SoCal in some warehouse distributor! Maybe have Santa Ana Speed do a search since they are a Holley dealer and have access to the "system"! I should have mentioned that before but I didn't think about that option since most of the time today it's not viable. And I bet the price on that kit is at least three times what ya paid for that blister pack!

Now...back to your questions...

The nylon washers ARE replacements for the older fiber-type bowl screw gaskets. For many years, the aftermarket has made similar available but they were some sort of crap PVC that cracked the first time they were snugged down (yes...Mr. Gasket and others)! But the Holley-supply nylon seals work just fine and I consider reusable unless badly distorted. The Holley service part nylon seals may be blue in color but will work as well as the white ones you see in your kit.

Thanks for jacking me up about the gasket deal...I'll get on that as soon as we have the Binder Bee wrapped for this year!

[RobertC]

FWIW -- though time consuming...

It looks like there is only one "hole" missing on your gasket -- compared to MM's post of the correct gasket. (If my "memory" is correct "flipping" between the pictures.) And, no "extra holes"...

Many years ago I used a leather punch (used to make holes in leather -- like holes in a belt) to "modify" the gasket for a Rochester H "secondary" carb to a Rochecter "primary" carb (Corvair 4-carb 140 engine).

Mark where the hole should be and place the gasket on a piece of wood...

The time consuming part would be finding a craft shop that carries leather punches and getting the correct size...

[kjc-01]

Robert,

That's funny you mention punching a hole for the vacuum bleed circuit, as doing that on the first throttle body gasket brought me here with all my questions!

-Jon

[RobertC]

I missed / forgot that from your original post.

I also missed MM's picture where the gasket needs to cover the "channel"...

[Michael Mayben]

The absolute STEAL in tools at Harbor Freight is the gasket punch set for under $5!!! I've punched THOUSANDS of holes with the 3/8" punch on a backup block of hard maple when making all those thermostat gaskets (I use a brass hammer on those punches). I also make the gaskets for the tank selector valves used in PickAlls with that set. Same for water pump gaskets when "shimming" the pump vane clearance, fule pump gaskets when needed, etc. ANYTHING except a head gasket, pan gasket, or lifter cover gasket, those are too much trouble.

Interface Solutions paper, cork composite, dead soft copper or aluminum, ANY type gasket materials can be cut with ease. If one of the punches gets dull, just sharpen it onna belt sander/grinder...or go buy another set or 10!