Wow I have a lot to learn here. Very helpful post Wjarjr! And really? Only a 55 was stock? That explains alot....looks like I'll be investing in a smaller jet for sure then! But yes, most of my driving is city with some highway. Idle is adjusted to the highest vacuum reading and per Dans instructions. The alternator pump rod has 3 holes in it for pump duration join believe. Currently it is set on the center of the 3 holes.

Yep, over the years of pulling Holley #1920 carbs off of engines, the leanest I found was #54, and the richest was #56... some people modding the 1920 found #58 was about the richest you want to go...

Holley 1945, could be had with the #58 jet stock in 1974 (it was pretty lean and made the heavy A-body gutless), #61 close limit jet in 1976 (typically a #612)... trucks in the late 70's would be a #62 close limit jet as well....

My 1945 had the 612 in it when I took it apart originally. I could never get that carb to run right. Maybe I'll look back into it this winter or I may just leave the 1920 on and tune it. Either way, looks like I'll be hunting for a #58 jet! I wish I could just go pick one up somewhere, but even the store that specializes in old derelict parts and stuff like that don't have any in stock

The jets are the same as the 4 barrel jets...so your options are to find a speed/performance shop and see if they have one, or you have to buy a pair from Holley over the counter at most regular auto parts stores...
(part number 122-58....)

There are two (physical) sizes of Holley jet, so they're not terribly difficult to get hold of. You can pay seven bucks for a pair of 56s or roughly double that for a pair of 57s.

I'd go with the 56s, m'self, especially since fuel economy is on your want list.

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Too many people who were born on third base actually believe they've hit a triple.

I've been told they're similar to the jets used in 4bbl carbs and warned of the 2 different sizes. But yeah up here (and by that I mean southern Wisconsin) all we have are your typical chain stores. Only one store around me even knows what a carburetor is frankly, so looks like I'm stuck ordering em online and waiting with anticipation.

Anyways, so Dan you recommend a 56? I've read quite a few posts in here saying they were borderline too lean and that many folks run 58s. I remember one post where someone said they ran a 62 jet in their 1920 carb and it made the car "feel" like it had a 318 under the hood. Hell running the 61 that's in it doesn't make it very like that at all!

But knowing the jet is substantially larger than it should be I guess that explains why on a cold start it blows soot everywhere like a diesel for a few minutes and why the only way to get the damn choke to work and the car to idle perfectly with it on is to hold the bad almost halfway open on a cold morning start.

Holley 57 jets ordered up amd should hopedully be here end of week. Hoping this is the key to the problems because id like to finally address some other issues with this car before i have to put her into storage!

LOL yeah, no.
Well, that's mostly a choke issue. Keep working on persuading yourself to get the electric choke kit. You'll be much happier after you do.

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Too many people who were born on third base actually believe they've hit a triple.

Haha I figured the guy yapping about his slant car feeling like a 318 was full of it.

But anyways, project update time! #57 jets came today. I went with 57's to make sure I wouldn't be running overly lean. Cleaned up the fast idle quite a bit and stopped blowing the black smoke all over even without the choke being fully open. Reset accelerator pump to the middle hole instead of having it on the most limited stroke. Runs decently, accelerates as best it can, and...blew the heater core. Awesomeness.

But since it finally seems to be running and ready for a mileage test, I think I may finally be able to re-visit the 1945 carb to see if I can find its faults (looks more original to the car which is why I wander back to it from time to time).

As discussed earlier in this thread, it appears to be the 1975 federal emission truck version of this carb so it should even have the larger venturi. Stock jet was a 621...close range 62. This thing eats more accelerator pumps than I eat Cheeto puffs. My plans are this:

- Mill all mating surfaces to make sure they are flat
- Rebuild with a Mike's carb kit
- wire wheel all linkages for choke and accelerator pump to remove burrs
- Install my 61 Jet into it instead of my 66 Jet

Can anyone tell me why this thing eats accelerator pumps and why the stream is always terrible at the start of the stroke? Seems like every 2 months I'm putting a dang pump in and they always rip on the top edge of the cone. They feel like they fit tightly down the bore for the pump until about mid-stroke, which is when they feel to loosen up. I've tried soaking them in brake fluid, wrapping a small spring under them to baloon them out (that didnt work at all), etc. But the stream is always weak and sputtery at the beginning but then is nice and healthy the rest of the way.

I've heard many people like the 1920 over the 1945 and vice versa for many reasons. Assuming the 1945 is salvable, which would you rather dump time into??

Call mike on the phone and ask him about this. It been years but these things swell up from todays gas. Get 2 of both sizes, see which works best. Mike is walker dealer and very helpful .One thing for putting it back together,take a hair blow dryer and warm the bowl ,and put top section in freezer.It will go back together this way, if using cup that has been in gas.New cups will usally drop right in .

By now should be some thing better than viton

Today's carburetor parts are made of materials compatible with today's gas; that TSB is not applicable because we don't live in 1977 and we aren't shopping for 1977 carburetor parts.

The most likely culprit is a rough spot or sharp edge in the accelerator pump cylinder that's tearing the cups.

As for which carb to put effort into: the one in better basic condition. The 1945 is a better basic design than the 1920, but many 1945s are equipped and configured along strangulation lines in accord with Chrysler's primitive, cheap and nasty emissions control strategy of the day. Some of this can be fixed, and I think we figured out you've already got a truck (larger, less strangled) 1945, so if it's in fundamentally sound condition that might be the smarter one to put work into.

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Too many people who were born on third base actually believe they've hit a triple.

I normally have to slowly work the new cups in for the accelerator pump with the aid of WD-40 or the gas left in the bowl (had to do this more than once with the carb on the car). They are always a super tight fit but feel ok moving them after they are installed. They only feel "loose" when they begin to move a bit more freely somewhere around the middle of the bore. I have used kits from HyGrade, Walker, GP Sorenson, and a different generic kit. All of them include the dark blue rubbery cups for the accelerator pump. And somehow they all rip. I'd like to THINK they are all the same size but....I frankly have no idea because I've never held them up side by side to compare them.

This carb has run stupid lean since the day I got it on the car. I chased everywhere under the hood looking for vacuum leaks with it installed, messed with timing (way too much...thankfully that's now fixed), and still the car ran and accelerated as if it was too lean! Only way to eliminate the horrible sag in acceleration off a standing stop was to pinch the accelerator pump linkage together and shim the cup internally.

Now it's back on my workbench...again. Gonna get this thing dialed in and rebuilt as soon as I have the time. Just wanted to get some opinions first and proper advice from folks with experience before banging my head on the wall again!