Author Topic: Carb recommendations  (Read 26123 times)

Offline Monkey Uncle

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Carb recommendations
« on: January 17, 2018, 06:08:33 AM »
I'm interested in any recommendations you might have for a replacement carburetor.

'78 GMC K15 chassis/drive train with an '85 C10 body
Remanned crate 350 (stock) with less than 500 miles on it, mated to an old TH350 that came from a third (unknown) donor vehicle
No emissions control equipment other than pcv hose running from driver's side valve cover into front of carb
Original stock air cleaner from the '78 truck
Carb, intake, fuel pump, and all ignition equipment re-used from the old engine
Fuel pump and fuel lines appear new

The intake appears to be the original stock intake from the '78 truck, but the carb is not.  The truck should have a 4MV quadrajet with divorced hot air choke, but it currently has a 1983 E4ME model with electric choke and several currently unused emissions features.  I am having some idle and driveability problems that were not solved by a re-build (details here if you're interested: http://forum.73-87chevytrucks.com/smforum/index.php?topic=35689.0).  It was better for a short while after the re-build, but now is even worse than before.  While it might be possible for a quadrajet expert to get it running right, I don't have such an expert available to me, so I think it's time to quit fooling with it and just replace it with a carb that is better matched to an old 350 with no emissions equipment.

From searching various auto parts websites, I see that there are remanned 4MV quadrajets available from National Reman, United, and Autoline for what appear to be reasonable prices with a 1 year warranty.  It also appears that there are several Edelbrock Performer and Holley Street Avenger models that are supposed to bolt on to my manifold, although prices for these are a good bit higher than for the remanned Q-jets.

Also my mechanic suggested that I consider a Carter aftermarket replacement with a manual choke.  I wouldn't mind the manual choke, but my searches did not find anything manufactured by Carter.  My understanding is that Carter is no longer in business, so any Carter carbs likely would be remanned, correct?

Any thoughts about any of these potential replacements?  Or any other suggestions?

Thanks.

Edit: I should explain how the truck is used.  It's a short distance errand/light to medium duty hauling truck.  Not exactly a DD since I don't use it to commute and probably drive it less than a thousand miles a year.  Although I like the cool factor of driving an old truck that is in pretty decent shape, it is not intended to be a show truck or a performance truck.  So I'm interested in a reasonably priced carb that will get me down the road with a minimum amount of fuss.
« Last Edit: January 17, 2018, 08:50:23 AM by Monkey Uncle »

Offline hatzie

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Re: Carb recommendations
« Reply #1 on: January 17, 2018, 10:02:28 PM »
Rochester Quadrajets were generally bulletproof grocery getter carbs that ran for long stretches with not much in the way of issues. 
The quality and care put into the rebuild job has direct bearing on how long it'll last.  Driveablility issues could be several things.  It could be as simple as the rebuilder didn't re-bush the throttle shafts or replace other worn internals.  The core might've been jetted differently from the original unit and the rebuilder didn't bother to check specs. The list goes on.

Some 1978 Quadrajets were manufactured by Carter under license from GM.  I replaced an original Carter 4MV Quadrajet on Dads' 1978 G20 Van with a reman back in the 80's.  Was surprised to see CARTER, not Rochester, cast into both units.  The being said Carter hasn't existed as a company since the late 1980's and manual chokes are a huge pain in the neck.  I would steer clear of "New Carter carburetors" and manual chokes. 

I'm not a huge fan of Holley carburetors on GM motors either.  My Ford F250 with an FE390 has a Holley right from the factory but that's a different animal.

In order to get a 4MV manifold mounted choke Quadrajet in 1978 you had to buy at least a 3/4 ton truck. 

The 1978 K10/K15 with 350 & AT should have a Rochester M4MC Quadrajet 17058503 or similar unit with a side mounted hot air tube choke.  It could also have come with a Carter M4MC Quadrajet with the same style choke. 
If you want a 1978 Rochester 4MV setup for very limited emissions and a manifold mounted choke you need to ask for a full ton chassis carburetor.  The 1978 K30 with 350 AT came with a Rochester 4MV Quadrajet 17055698 or similar unit.  If you can find a quality rebuilder that can sell you one of these I'd run it.

You're letting the truck sit for long periods of time so you should find "real" gasoline without the mandated Ethanol to corrode the carburetor.

« Last Edit: January 17, 2018, 10:08:07 PM by hatzie »
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Offline Monkey Uncle

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Re: Carb recommendations
« Reply #2 on: January 18, 2018, 05:20:57 AM »
Thank you, hatzie.  That was kind of my instinct on the Carter carbs when I did a search and didn't turn up much.

I left out a potentially important piece of information - the '78 truck originally had a 4-speed manual transmission.  Not sure if that makes a difference in which carb model the truck would have been equipped with from the factory.  At any rate, I believe the intake does have the well for the divorced choke (see photo).  I have the old title for the '78 truck and have used the VIN to look up the specs - it definitely was born a 1/2 ton truck.  I suppose it's possible someone could have swapped out the intake at some point.

I do use E0 gas.  Expensive, but worth it.

Offline Stewart G Griffin

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Re: Carb recommendations
« Reply #3 on: January 18, 2018, 12:20:40 PM »
If you're only going to put 1000 miles on it per year, then i would just leave the carb on there and put up with the minor driveability issues;  If you leave the truck sitting for a few days, having to crank about 10 seconds before starting is not TOO abnormal (i don't think?).

2) The "reman" carbs from national/United/Autoline etc. are likely JUNK----unless you don't mind taking them apart and checking them over---maybe (though they still could be junk), in which case, you might as well take the one you already have apart and rebuild it.....................
Generic remans
a) may not be put together with good care
b) tend to be rebuilt to general, one size fits all, specs vs. the specs for your particular application.  Example: one part number may apply to a 78 monza with 305 AND a 78 3/4 ton truck with 350 and everything else in between........

3) Now, if you really think you need a new carb and are unhappy with what you got now, then:
http://www.jegs.com/c/Fuel-Carbs-Intakes_Carburetors/10271/10002/-1?N=1010271+4294961605+900555&Ns=P_PrimarySecondary%7C0%7C%7CP_SalesVolume%7C1&Tab=SKU

You may want to consider #15803

Summit has equivalent part numbers.   i think these carbs may be rebuilt by JET and i think they are good quality rebuilds, unlike the 3 companies listed above.

i run the #15805 on the v-6 and it runs pretty good.


Offline Monkey Uncle

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Re: Carb recommendations
« Reply #4 on: January 18, 2018, 07:36:36 PM »
Hi Stewart - the drivability issues are getting to the point that I don't want to put up with them any more (running extremely rich; erratic/rough idle, sometimes to the point of stalling out; poor cold weather performance; very poor fuel economy).  I know these things should be fixable, but it's finding someone locally who is up to the task that is the problem.

I appreciate you sharing your opinions on the budget remanned carbs.  I've read widely varying opinions of them in various forums and online reviews, which suggests to me that quality control is iffy.  Maybe I get lucky and get a good one, or maybe I get one that wasn't put together right.  Do you have first-hand experience with these brands, or know someone who does?

The #15803 model on the jegs website costs more than some of the new Edelbrock models, which makes me wonder if I should just go aftermarket.

Offline Stewart G Griffin

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Re: Carb recommendations
« Reply #5 on: January 19, 2018, 01:51:12 PM »
Ok, i admit that i did run a reman carb (i think it was National, but not sure.  Whatever Pepboys carries..) on the 305, when i was running a 305 and it ran pretty good.  So maybe they are not all "JUNK" so much as poor quality but more so they are probably not calibrated optimally to your specific application.

2) i'm not familiar with the Carter AFB (which is what i think the Edlebrock carbs are a copy of?), but knowing Edlebrock, they are likely very good quality.

http://www.jegs.com/i/JET-Performance/561/33009/10002/-1

Ok, it's a marine carb, but it should work just fine on the street?   Also, it's calibrated for a 350.   JET is high-quality.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #6 on: January 22, 2018, 08:30:46 AM »
I was looking at the National website yesterday and noticed that they have "new" quadrajets for sale, in addition to the remanned carbs.  I was scratching my head over that since Qjets haven't been produced for decades.  So I called and spoke with a nice gentleman there, and he told me that they had some new Qjet castings made and built essentially new carbs from the ground up with all new internal parts.  These carbs come with a lifetime warranty, and are priced competitively relative to the high-end remanned carbs sold by Jegs and Summit.  Of course, even with all new components, the quality of the carb still depends on the knowledge and care of the person who assembled it.  Do any of you have any experience with or knowledge of these "new" quadrajets?

Offline 75gmck25

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Re: Carb recommendations
« Reply #7 on: January 22, 2018, 05:26:23 PM »
I don't have any info on the quality of the re-manufactured or new Quadrajets, but do have some other comments.

I initially tried using an Edelbrock 1406, which is a really common square bore replacement for these trucks.  However, when I finally installed an AFR gauge and started playing with rods and jets from the Edelbrock kit, it always seemed to run too lean to get good performance.  It was okay, but never quite right.

I then bought a junkyard Quadrajet off an '86 1 ton C30.  Truck carburetors were updated later than GM cars, so this was one of the last models with no electronic controls.    I bought a complete rebuild kit from Cliff Ruggles, including throttle shaft bushings.   Once I rebuilt it and played around a little with the mixture and secondary engagement mechanism, I found it to be a great carb.  With the stock jets and rods it runs at an AFR of about 13.9 most of the time, but I can watch it go richer (about 12-12.5) as I tip in the throttle and it goes to the secondaries.  I also converted it to an electric choke and blocked off the hot air mechanism.

The only downside I have heard about the National rebuilt carbs is that the configuration is not always a good match to your vehicle.   Its hard for them to do mass market re-manufacturing and still have the carb well matched to a certain vehicle. If you look at the specs for original Quadrajets, there is a lot of variation between vehicles.

Bruce

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #8 on: January 22, 2018, 07:28:14 PM »
Hi Bruce,

I've been looking at the Edelbrock 1405/1406 carb also.  Not crazy about it as it clearly would be a retrofit exercise.  I'm sure it would work o.k. for my non-performance application, but it kind of feels like the proverbial square peg in a round hole.

Do you know the model of the '86 qjet?  Sounds like it is not an electronic carb, unlike my current E4ME.

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #9 on: January 29, 2018, 02:35:36 PM »
After doing a lot of poking around and getting a lot of off-line help from Henry (thanks Henry!), I realized that I had misidentified my carb model.  It is not an E4ME, it is an M4ME.  As I understand it, this is basically a normal Qjet with an electric choke, which should work fine on my engine.  So I've been considering whether I can make this puppy work instead of springing for a replacement. 

It recently had a standard auto parts store rebuild kit put in it (this was done by a local mechanic, not by me).  I am not ruling out the possibility that something was done wrong during the rebuild.  If it was rebuilt correctly, it clearly was not tuned correctly, or it has internal problems that were not addressed by the kit.

The biggest problem I'm having is that it is running way too rich, to the point where it smokes, blows soot, and the exhaust smells strongly of gasoline.  So I adjusted the idle mix screws to see if I could get it to lean out.  I know this is not a substitute for running through the full tuning procedure, but before I dive into that, I wanted to see if it is even possible to get it out of its rich condition.

I have never messed with the idle mix screws before.  The engine was fully warmed up after about an 8 mile round-trip to the store.  Based on instructions I've read, I was expecting to tighten each screw a turn or two until the idle started to stumble, and then I would back off.  I actually was able to turn them all the way until they felt like they seated, and this produced just a little bit of burbling in the idle (turning one screw at a time, of course).  Is this normal?  I had anticipated that it wouldn't run at all, or would run very poorly, with one of the mix screws tightened all the way in.  I only noticed slight variation in the speed and character of the idle throughout the range of travel of the screws.

At one point during the process, I revved the engine, and the rpms dropped down to a low idle.  Apparently it had been stuck on high idle since the carb rebuild.  I had noticed for a while now that it was idling pretty fast once it warmed up, but I had not been able to get it to drop down by goosing the pedal.  Would adjusting the mix screws somehow allow it to drop off of high idle now? 

After it was on low idle, I fiddled with each mix screw until the idle sounded best, which was about 2 turns out for each screw.  But when I put it in gear the engine idled slow and rough.  I increased the idle speed using the base idle screw, but still had to back the mix screws out to a total of 3 1/2 turns to get the engine to idle reasonably well when it's in gear.  I couldn't get the idle to clean up completely - it's still kind of rough, but it doesn't seem to be in danger of stalling.  I realize I should be doing all this with an RPM meter to get the idle set to spec, and should also be checking/setting ignition timing, but I wanted to see if the richness issue would respond favorably to adjustment before investing in more tuning tools.

The adjustments appear to have leaned it out some, as evidenced by lack of smoke and a reduction in the gasoline smell in the exhaust.  But the exhaust does still smell like gas a little, and I noticed some soot blowing out when I revved the engine.  I suppose it might just be blowing accumulated soot out of the exhaust system.  Any good indicators I should be looking for to determine whether tuning has fixed or can fix this richness issue?


While doing all this, I noticed two other problems.  The choke flap was only slightly open (see first photo) during the entire adjustment procedure, despite the engine being fully warmed up and despite it idling for probably 45 minutes while I was fiddling with the screws.  Outside temp was in the upper 30s - chilly, but I would think that at that air temp, the choke should still be fully open after an 8 mile drive.  After adjusting the mix screws, I test drove a few more miles and then parked the truck without looking at the carb.  About an hour later, I went out and pulled off the air cleaner and the choke flap was almost fully open (see second photo).  Is this choke behavior normal?  If not, is there anything I can do to adjust it?

The second problem is that the OEM air cleaner is not seating quite right.  It is about 1/16" to 1/8" off the gasket in the back.  It is hitting a metal vacuum tube that comes up off the back of the intake and then turns and goes down toward the transmission (see close-up photo).  Would it be possible to bend this tube slightly to get it out of the way of the air cleaner?

O.K., that's an awful lot - sorry for the long post.  Any help is greatly appreciated.

Offline Henry

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Re: Carb recommendations
« Reply #10 on: January 30, 2018, 11:47:08 AM »
Hi:
First problem sounds like your choke rod and fast idle setting may be out of adjustment and/or you are missing a linkage or two that controls the position of the choke valve (flap). Sorry, I dont have a adjustment picture for the choke rod on the M4ME...maybe someone else does (usually comes with the rebuild kit). You may need to remove your choke housing to make the adjustments. Some time ago I think I sent you an exploded illustration of the M4ME...do you have this?....although this does not show how to do/check the linkage adjustments at least it will show you what linkages you should have on carb.

Second problem: yes, it is a close fit between the air cleaner housing and that vacuum fitting and distributor. My air cleaner has a "dent" in it to just make enough clearance. You can bend the metal pipe a bit backwards, as mine has this bend in it...just make sure you dont kink the line. Maybe you can replace the short little rubber hose at the bottom of the metal line with a longer one that can bend backwards a little more.

Regards,
Henry

Offline Henry

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Re: Carb recommendations
« Reply #11 on: January 30, 2018, 11:56:43 AM »
Hi:
By the way, can you post close up pictures of the front and drivers side of your carb?
Henry

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #12 on: January 30, 2018, 02:03:54 PM »
Hi Henry,

Yes I do have the M4ME diagram that you sent me.  I studied the choke linkage parts, but I can't seem to match the drawing to the linkage parts that I'm seeing on my carb - they don't look like the same parts to me.  But I don't have much experience with exploded parts diagrams, so maybe I'm just looking at it wrong.  The first last picture below is a close up of my choke linkage parts. 

When I operate the choke linkage by hand, the flap moves through its full range of motion, from almost completely closed as it was depicted in the picture above, all the way to fully open. 

My rear vacuum break also looks different from the one in the diagram.  Mine has two linkage attachment locations that are oriented parallel to each other.  The one that is closest to the body of the carb is connected to the linkage that goes to the choke.  You can see this black linkage in the second first picture.  When I operate the choke by hand, the black linkage moves back and forth, but the linkage attachment on the vacuum break doesn't move - the linkage just slides back and forth along the slot in the linkage attachment.  The other (outer) linkage attachment is supposed to connect to the secondary air flap, but the linkage is missing (this was pointed out to me in the previous discussion thread on my carb).

The third second and fourth third pictures are close-ups of the front and driver's side of the carb.

I tried bending the vacuum tube, but it wouldn't budge.  It seems like the steel tube goes down through the short piece of rubber hose such that the tubing is inserted into the fitting in the top of the intake.  The tube appears to be glued into the fitting with some sort of epoxy.  Not sure what the piece of rubber hose is for.

(Edit: fixed incorrect photo references.)
« Last Edit: January 30, 2018, 02:07:24 PM by Monkey Uncle »

Offline Henry

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Re: Carb recommendations
« Reply #13 on: February 01, 2018, 11:44:18 AM »
Hi:
Your older posts about adjusting the mixture screws to try and change high idle and  richness of the engine are all abnormal. Lets start with the choke system: You are missing your primary vacuum break assy (front of carb on pass side). The vacuum connection for it is on the float bowl housing (big center body of the carb), front, top. You have a hose on this connection which runs to the back of the engine probably to the distributor...this is wrong. The hose from the distributor needs to transition to the metal hose (do you still have it?) and then back to another short rubber hose that plugs into a vacuum connection on the float bowl body, front, drivers side, low)....this is probably capped right now. The larger port on front, center of the float bowl housing is for the connection to the Evap Emission System cannister that may or may not be in your engine bay anymore...usually on the driver side fender well or maybe even on the front drivers side near the radiator...in any case you can leave it open for now if there is no connection. Secondly, from your photos, it appears as if your electric choke is incorrectly set...maybe as far as 180 degrees out. On the plastic cap, there should be a little pointer that should be pointing at the cast in hash marks on the front of the choke coil housing...you should be able to loosen the screws and turn it until the pointer comes to the middle of the hash marks. Thirdly, the rear vacuum break should have a vacuum hose that runs to the back of the carb...connection should be low down and maybe  on the throttle plate (lower cast part of the carb) in the middle. There should be a long straight linkage from the primary vac break diaphragm to the link on the secondary throttle shaft on the choke plate (air horn or top cast part of carb). There should be a short link from the secondary vac break diaphragm to the same little link on the secondary throttle shaft. Then there should be a third linkage that goes from the secondary vac break diaphragm to the intermediate choke shaft, lever, and link assy...this is partially hidden behind the choke coil. I see you have a painted black linkage laying in there but I cannot tell what it connects to by your photos. Next, you need to connect the THERMAC vacuum hose to the connection that is below the choke coil...is this vacuum port there on the carb? From the photo on the drivers side, it appears you are missing the anti-dieseling solenoid...this is probably OK to leave this off for now...do you see a wire laying around to connect to it? Next, that pesky intake manifold vacuum connection behind the air cleaner: it should be a little T-port threaded into the manifold. The top connection (larger) goes to a short big rubber hose that the metal pipe connects to. There should be a side connection (smaller) that a rubber hose goes to that runs all the way over to the vacuum accumulator mounted on the firewall on the passenger side of the engine bay...it is a little round plastic can. It sounds to me that somebody broke the T-port threaded connection to the manifold and glued it back without the T-connection...you can buy one of these from one of the catalog websites. From the photos your carb looks like it is leaking from all the gaskets. Let me see if I can find a good straight on graphical image of how the M4ME choke linkages are supposed to be...maybe someone else on the forum can show what theirs looks like. While I was writing all this I was humming that old song by BJ Thomas: "Another Somebody Done Somebody Wrong Song".
Regards,
Henry

Offline Monkey Uncle

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Re: Carb recommendations
« Reply #14 on: February 02, 2018, 06:45:56 AM »
I'll have to go from memory on all of this.  Took the truck to the shop last night for a final valve adjustment on the new crate engine, as I was starting to hear some ticking.  When the mechanic took the valve covers off, we saw that one of the rocker arms had slipped off of its contact point on the lifter.  This is the second time this has happened, so I left the truck with him so he could replace all of the rocker arms (under warranty).

Not sure what's up with the primary side vacuum break.  I've seen lots of photos and a few diagrams of M4MEs that don't have one, but who knows how those carbs have been butchered over the years.  I have noticed that all of the photos I've seen of carbs that have both primary and secondary side pull-offs have the primary side pull-off connected to a vacuum fitting that does not exist on my carb.  This fitting is in the air horn right next to the aneroid chamber (top front passenger side corner).  On the photos I've seen of carbs with only a secondary side pull-off, this fitting is absent, as on my carb.  But they all have the screw holes where a primary side pull-off could be attached.

Yes, that hose you're seeing that is connected to the fitting on the front passenger side of the float bowl housing is the distributor vacuum advance.  I do still have the original vacuum advance tube, which could be used to connect the advance to a currently plugged fitting on the driver's side front of the fuel bowl.

I do not have a charcoal canister.  Are you saying that the fitting for that should remain unplugged?  Currently it has a rubber cap on it.

Yes, the choke was very badly out of adjustment, which is why it was not opening fully even after running the engine for a long time.  I adjusted it yesterday and improved that situation some.  Unfortunately the choke cover does not appear to have any reference marks on it (at least none that I could see through my bifocals).  I set it such that the choke flap was open a small crack at an ambient temp in the low to mid 40s.  This setting has it rotated about 70 degrees clockwise from where it was in the pictures above.

Prior to making that adjustment, I went through the checks outlined here: https://www.corvetteforum.com/forums/c3-tech-performance/1024531-q-jet-adjusting-electric-choke.html.  The measurements all seemed to be set to the proper specs.  However, I wasn't able to do the suck test on the vacuum break.  The hose attached to it didn't want to come off, and it seemed to be old and fragile enough that I was afraid I would tear it (I didn't have any replacement hose on hand - obviously I need to replace this hose at some point).  But I actuated the vacuum break by hand and took the noted measurement, which seemed to be o.k.  I'll need to check the function of the vacuum break once I get some replacement hose. (This also answers your question about whether the vacuum break has a vacuum connection to the carb - it does.)

I also re-set the fast idle screw to the base setting according to the directions at the link above.  When I started the engine, I had to tweak both idle speed screws a little faster than the base setting.  Yes, I know I need to get a RPM meter and set idle speeds according to spec, but for the time being I was just trying to keep the engine from running rough/stalling when I put the trans in gear.  After setting the fast idle, I was able to get it to kick off by tapping the pedal.  Previously it had wanted to stay stuck on fast idle.

Now the choke at least opens as it should after the engine warms up.  Idle is still rough - not slow and lopey, more fluttery like it's missing.  It's worse when the engine is cold, but even after it warms up some fluttering remains.  Giving it any pedal at all eliminates the flutter - it runs smoothly while I'm driving down the road.

The rich condition appears to have been mitigated quite a bit.  I think it is still running too rich based on the smell of the exhaust, but it is no longer smoking and blowing soot, and the exhaust doesn't smell as bad as it did before.

There is a linkage connecting the secondary vacuum break to the choke shaft assembly - it moves when the shaft assembly is rotated.  As you noted, the link to the secondary air flap is missing.

Going from memory here, but I don't recall a vacuum connection below the choke coil.  On my previous carb thread, one of the posters suggested that Thermac hose on the air cleaner should connect to the vacuum fitting on the rear center of the air horn.  I haven't tried to make that connection yet.  I will also need to find something to cap off the pcv inlet on the side of the air cleaner.  The valve covers have been replaced with aftermarket covers (OEM covers wouldn't seal up right after the engine swap), and the new cover does not have a pcv vent on the passenger side.

You are correct that the carb does not have an idle stop solenoid.  I've never had any issues with dieseling, so I'm inclined to forgo that part for now.  I have not seen a wire in that vicinity, although there is a stray wire with a plastic connector on the end of it that comes from somewhere near the middle of the firewall.

The intake manifold vacuum port has the T connector, and the side connector is connected to a hose, but the hose runs toward the driver's side of the firewall, not the passenger side.  Going from memory I can't recall whether it terminates in a plastic can.  The top of the T connector does not appear to have a nipple on it - the solid vacuum tube is glued into the top of the T connector.  The steel tube appears to run through the short section of rubber hose - not sure why the rubber hose is there at all, unless it was just left in place when the steel tube was glued directly into the fitting.  I suppose the only way to remedy this properly is to replace the T connector with one that has the appropriate nipple for attaching a short section of rubber hose?

I snugged down all of the screws in the top of the air horn.  They were all a bit loose; apparently the gaskets are still settling in from the rebuild.  We'll see if this stops the seepage.

Thanks very much, Henry.