74 Slant 6 Bogs & Stalls Under Load / 30 mph

[74DartSwingerCapeCod]

New to working on a Slant 6, with limited mechanical ability. It's been running okay, not great, and here's what's going on now. (Slant 6 forum has been slow to bestow me a new log in, but Ive seen that some of those folks also frequent this board, like Slant Six Dan, who seems to really know his stuff)

Have a 74 Dart Swinger, pristine body & interior and a Slant 225 (with a/c and a a904 automatic) that was brought back to life a few years ago following a 25 year covered, garaged, nap. Mechanic dropped the fouled tank, replaced carb (installed a Holley 1920) cleared it the lines prior, changed oil, coolant, plugs, wire, distributor, and she fired up reasonably well. Drove it for about a year here on Cape Cod locally, as the 1920 carb would stall on me during left hand turns. Lol. I got creative in my travels.

Last year, replaced 1920 for a Holley 1945, which I read was original on a 74. Left hand turn prob was gone, and it ran pretty well for a year on local Sunday joyrides. Replaced water pump, alternator, radiator, master cylinder, brake hoses and similar incidental items just as proactive maintenance. All good.

This past summer (2021) ran great - but always had a bit of a bog upon sharp acceleration - (yes I know it's a 6, not an 8) but yet, it was drive able and enjoyable.

Early this fall, I drove it over to the next town, gaining confidence in its performance, when all of a sudden following an extended parked idle at a friends house, (30 mins) on the way home, it died upon acceleration at approx 40 mph. First sensation was a lack of response in acceleration, then just a total bog down, which resulted in a total stall. 5 minutes later after a few labored cranks, she drove me home (only about 1 mile) at low speed with no prob.

So... I replaced the coil, ballast resistor, ignition module, voltage regulator. Checked all wires and vacuum hoses to make sure connected. All were fine. (I dont know how to check actual vacuum readings, beyond my expertise for now) Tried car again. Fired car up, idle was uneven. Surged and retreated, but evened out. Tried driving on level road at speed. It died in the same manner, bog on acceleration once warm at about 30-40 mph. Restarts after about 5 mins, and I can limp home at slow speed.

Researched this, and replaced EGR valve with a NOS appropriate Mopar part. Old one had a bit of carbon, but seemed alright. No change. Same symptoms. When it stalled again under load in drive at 35 mph, I did hear a bit of a quiet backfire as it died on the road.

Convinced I'm looking at fuel now rather than electrical, I re calibrated carb settings (mix and idle) by setting screws and backing out 2 1/4 turns each on the Holley 1945. Figured it's drowning on fuel? It Idled perfectly, but after about 10 solid minutes of smooth idle in park, she just dies. Not a pronounced deterioration to idle, just a brief choppy span, and it deteriorates to a stall.. like a 15 sec death.

Idle does seem to have a very subtle "fart" to it, really hard to hear. At this point I'm imagining things. But... something is definitely wrong, and I'm guessing its fixable due to these symptoms, I just can't figure out what it is based on my limited expertise.

So... I'm thinking vacuum advance on distributor, or distributor pickup? Timing off? Fuel filer seems clear. Mechanical fuel pump? (Which was replaced at resurrection)

Btw, tranny seems to shift fine prior to under load death, hoping it isn't the tranny.

I'm bringing it to a mechanic, who is more experienced than I am, and I'm going to explain this same timeline of events to him. He has better tools than I do!

Thoughts...

a) this has to be something traceable, fuel wise. Electric choke? Pain in the butt emissions crap? Such as vac amplifier etc? (Osac has already been routed to bypass air cleaner housing straight to distributor)

b) heard the carter bbs is a better simple hassle free carb than the holley. Will a 300 dollar expenditure be worth it? I can get one that’s supposed to be for a 70-71 slant truck. Fit?

c) should i upgrade to a super six set up... clifford or aussie 2bbl intake with a carter (or is it weber bbd) running with stock exhaust for the hope of greater reliability? That's about 1k in parts when I'm done- plus linkage, as I'm in no position to hunt graveyards. (Btw, manifold head bolts all look clean.. and so this could be do able)

d) Eventually ( I know this is slant 6 blasphemy) drop a 360 crate in it, update the 904 tranny to a 727 and update the rear end 7.25 to an 8.25 sure grip posi. Sure, that would be more than nifty, but I'm also content to just have a reliable 6. Plus, it would cost the better part of 10k.

If this was your child, what would you do ?

Thanks!!

Gregg

 

[my68barracuda]

For a motor to run it needs: air+fuel+ignition.
If the engine is stalling during an idle or while being driven one of those is dropping out.
Some simple analysis could point you in the right direction.
Right after it stalls, remove the air filter housing and with the engine still off look down into the carburetor and open the throttle fully with a quick motion. You should see a healthy fuel squirt into the carb venturi. If you do, that’s good, if you don’t that means that either the accelerator pump is mid adjusted or defective or the carb is running low on gas. Running the carb low on gas is normally a weak fuel pump or it could be a clogged line or plugged filter.
If the accelerator pump flow is normal, and the air filter looked good when you removed it, one more way to check for a fuel problem is to remove and do a visual inspection on the spark plugs. Very black plug ends is too rich, very white plug ends is too lean.
If the plugs also look good, you can have confidence the issue is not fuel or air related and is likely a spark-ignition issue.

 

[66fs]

Get a rebuilt Carter. New fuel filter, maybe an electric fuel pump. Bypass or delete all emissions garbage. Adjust the valves, and adjust initial timing to 5*- 10* BTDC. Check to be sure the vacuum advance is good. That thing should run like a champ.

 

[67Dart273]

The EGR will not affect idle/ low speed UNLESS the valve is leaking past WHEN CLOSED. Remove vacuum line from EGR, plug, and see if it improves. If you suspect it, make a block off plate (simple, scrap of strap and a bolt hole, some silicone sealer)

Idle mixture. You do NOT adjust idle mixture by "backing out" the screw and leaving it. You adjust it by 1....with engine otherwise tuned, AKA valve adjust if applicable, clean functional plugs, plug wires, cap, rotor, good (not sloppy worn) distributor, SET THE TIMING and not necessarily at "sticker" spec..................

Then with engine FULLY warmed up you set idle speed and idle mixture, and you may have to "go back and forth" because if the mixture is "off" far enough, it will affect idle RPM

So with all of the above, now adjust mixture. With engine at proper idle speed in park, adjust screw carefully "out" some (rich) then CW until engine "peaks" in RPM and then "starts" to fall off peak. Repeat to find "peak" you want it just slightly "lean" of peak without losing RPM so to say. Maybe about 1/8--1/4 turn CW from peak.

Some cars "like" to be set "in drive." Obviously THIS CAN BE DANGEROUS. Second person to hold brake is just about mandatory, unless you have some 100% safe method of chaining the car to a "tree."

Use a tach (dwell tach) or vacuum gauge or both to set idle. Max vacuum, max RPM

1...Generaly inspection, adjust valves, compression / leak down test
2....Replace as necessary plugs wires cap rotor etc etc
3....Adjust breaker points gap/ dwell if applicable. Inspect distributor for wear as well, and if breakerless, inspect reluctor/ pickup for strike damage, rust/ debri, etc
4...Set timing, test for mechanical and vacuum advance operation
5...Last set idle speed and mixture. Before doing, you should have inspected all vacuum hose routing and hookup, PCV, power brakes, EGR, choke pull off if used, etc etc for leaks and proper hookup.

 

[74DartSwingerCapeCod]

Get a rebuilt Carter. New fuel filter, maybe an electric fuel pump. Bypass or delete all emissions garbage. Adjust the valves, and adjust initial timing to 5*- 10* BTDC. Check to be sure the vacuum advance is good. That thing should run like a champ.

66fs, I can get a Carter BBS that's supposedly for an earlier slant. This place has several. CARTER 4956S BBS CARBURETOR
Assuming I would definitely need to lose the emissions with thiscarb, as it may not have all the ports. Do I just block off any old emissions ports with vacuum caps? If you think one of these bbs carbs will fit my 74, I think I'll try this route as you suggest. I'll have someone help me with timing, if I see it done I can learn for next time. Thanks !

 

[66fs]

I would think someone on this site would have one much cheaper. Heck, I used to give them away. You don't need to ditch the emissions, per se, but render it inoperable to simplify the system. Start with the simple/cheap stuff, replace the fuel filter, test the fuel pump pressure. Can you rebuild the Holley? You have electronic ignition, no catalytic converter. Adjust the idle mixture by screwing it in until it starts to drop rpm, then back out 1/4 turn. That should get you close.

 

[slantsixdan]

New to working on a Slant 6, with limited mechanical ability.

As soon as you can, get the three books listed in this thread and start readin'!

Tune-up parts and technique suggestions in this post. Pay careful attention to the spark plugs: were good ones put in? Did the installer know to remove the metal ring washer from each spark plug before installing it? Pay similarly close attention to the quality of the other replaceables in the ignition system—distributor cap, rotor, plug wires, ignition box, etc.

Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

Last year, replaced 1920 for a Holley 1945, which I read was original on a 74

It was, but the first few years of the 1945 carb, which started in '74, were godawful. There were numerous revisions and tweaks to them, attempts to address a bunch of design and calibration flaws, while at the same time emissions standards were growing tighter, so Chrysler and Holley were in a tight spot and these carbs were jetted very lean. A thoughtfully-chosen new 1945 carb, skillfully rejetted, can run well. There is virtually zero such hope with a "remanufactured" carburetor (1945 or any other model), no matter what name is on the box. But new old stock Slant-6 carburetors have grown really scarce and costly any more, so now you're the one stuck in a tight spot.

So... I replaced the coil, ballast resistor, ignition module, voltage regulator.

I understand the urge to do something about the problem, but…stop doing this. Throwing parts at the car like this is an efficient way to drain your wallet, but will almost never fix the problem—in fact, you can easily worsen it, because a lot of the parts on your list are now no longer available through usual parts sources in quality worth having, and you can replace a good/old part with a crap/new part. More than that, if you take this shotgun approach and you do happen to accidentally fix the problem (or seem to fix it), you won't know what the problem really was and you'll learn nothing about how the car works.

Instead of just buying parts at random, you will need to do some diagnosis to home in on the problem and figure out what needs to be fixed, adjusted, or replaced. That's why my first advice was to get and read those books. Yes, this will take some time and effort…that goes with the territory when you own an old car.

bog on acceleration once warm at about 30-40 mph. Restarts after about 5 mins, and I can limp home at slow speed.

If I were faced with a car that would stall like this and refuse to restart until some number of minutes had passed, one of my first suspicions would be that there's still trash in the fuel system. You mention the tank was dropped and cleaned—perhaps not all the crud was cleaned out, and/or perhaps the mechanic reinstalled the old strainer (or no strainer at all). Or maybe that's not it, but there's trash in the upstream side of the fuel filter. Either way, what can happen is that the trash gradually gets sucked up against the filter sock in the tank and/or the dirty side of the fuel filter, then when you punch the gas there's not enough fuel flow to meet the engine's needs and it dies. Your five minutes are spent waiting for the trash to float back off and away from the strainer and/or filter, then the engine will start again.

But that's just one thing that could cause this problem, it's not the only thing. Could easily be a fault in what I'm guessing is a "remanufactured" 1945 carburetor, among other possible faults.

Researched this, and replaced EGR valve

This, as you found out, was not the solution. The symptoms you describe are not those of a faulty EGR valve. Be careful not to confuse research with reading stuff on the internet. They aren't the same. There's a ton of bad advice available for the asking (or clicking). Some of it right here in this thread; for example, no, you do not need/will not benefit from an electric fuel pump. No, you should not fling open the hood and pretend to be a caveman ("Hurr, derp! Emission crap bad! Hulk smash! Hulk rip! Grr! Snarl!").

I did hear a bit of a quiet backfire as it died on the road.

Spitback is a symptom of a very lean mixture, and since your engine appears to be starving for fuel, a cough like this as the engine dies is in line with expectations.

I re calibrated carb settings (mix and idle) by setting screws and backing out 2 1/4 turns each on the Holley 1945.

Sorry, no. You did not recalibrate anything. There is no magic number of turns (2-1/4 or any other) where any screws are supposed to be placed. That's just not how any carburetor adjustment is actually done. Info on how it's actually done is in that carb-manuals thread I linked.

Figured it's drowning on fuel?

No, opposite.

So... I'm thinking vacuum advance on distributor

No.

or distributor pickup?

No.

Timing off?

Maybe so, but that would be on top of whatever's causing your symptoms.

Fuel filer seems clear.

As determined how?

Mechanical fuel pump?

No.

Btw, tranny seems to shift fine prior to under load death, hoping it isn't the tranny.

It's not.

Electric choke?

No.

Pain in the butt emissions crap?

Probably not.

heard the carter bbs is a better simple hassle free carb than the holley

Yes, but they are hard to find in condition worth having. The optimal one for your '74 would be the '73-'74 Dodge truck BBS, and those have never been particularly easy to find. The further back you go from there, the more adaptation will be required. None of it's terribly difficult, but beware of "feature creep"—none of these BBS carbs has a provision for venturi vacuum, which you need if you're keeping your EGR system operational, and there is no workaround for this. If you disable the EGR, you will likely have to recurve the distributor to avoid damaging ping/knock.

should i upgrade to a super six set up

The Super Six 2-barrel setup gives much better driveability, performance, and economy than the wheezy 1-barrel setup, but it requires a pretty long list of parts, some of which have grown very difficult and/or costly to buy, and you'd still need to find and buy a good carburetor.

clifford or aussie 2bbl intake

No, neither. Those are race/hotrod pieces, not appropriate for your engine configuration or the kind of use your car gets. You would be paying expensive money to doom yourself to endless hassles trying to get the car to run right. If you want to take on a 2bbl swap—which I do not recommend until you have a stronger working knowledge of how cars like yours are put together and what makes them run—you would want to stick to mostly factory-type Super Six components.

Eventually ( I know this is slant 6 blasphemy) drop a 360 crate in it, update the 904 tranny to a 727 and update the rear end 7.25 to an 8.25 sure grip posi

This is not the way to fix the problem. If that's the kind of car you want, go find and buy it—if you set out to turn your existing car into this what you describe, you will spend a staggering amount of money and the overwhelming odds are that if the project actually gets completed—which it probably won't—you will wind up disappointed and unhappy.

If this was your child, what would you do?

Read, learn, diagnose, repair.

 

[74DartSwingerCapeCod]

I would think someone on this site would have one much cheaper. Heck, I used to give them away. You don't need to ditch the emissions, per se, but render it inoperable to simplify the system. Start with the simple/cheap stuff, replace the fuel filter, test the fuel pump pressure. Can you rebuild the Holley? You have electronic ignition, no catalytic converter. Adjust the idle mixture by screwing it in until it starts to drop rpm, then back out 1/4 turn. That should get you close.

I would think someone on this site would have one much cheaper. Heck, I used to give them away. You don't need to ditch the emissions, per se, but render it inoperable to simplify the system. Start with the simple/cheap stuff, replace the fuel filter, test the fuel pump pressure. Can you rebuild the Holley? You have electronic ignition, no catalytic converter. Adjust the idle mixture by screwing it in until it starts to drop rpm, then back out 1/4 turn. That should get you close.

66fs, Thanks for the advice, and also thanks for the understanding whereas I’m new to all this. Kinda takes the pressure off, and that’s a good way to learn. Hopefully I’ll have some time to futz with it around Thanksgiving. I’ll keep you posted! G

 

[zmarty27]

I would think someone on this site would have one much cheaper. Heck, I used to give them away. You don't need to ditch the emissions, per se, but render it inoperable to simplify the system. Start with the simple/cheap stuff, replace the fuel filter, test the fuel pump pressure. Can you rebuild the Holley? You have electronic ignition, no catalytic converter. Adjust the idle mixture by screwing it in until it starts to drop rpm, then back out 1/4 turn. That should get you close.

I experienced similar issues with my own. A carb rebuild worked wonders for me and I run the same 1945.

 

[RGAZ]

Maybe its me, but it sounds like you may have a vacuum leak. Easy to check, start car at idle and spray carb cleaner around all vacuum hoses and manifold. If the engine revs up where you spray a spot, that is your leak (check near and under carb). I am a little surprised this was not mentioned or tried before you started replacing parts.

Good luck,
RGAZ

 

[slantsixdan]

Match the suggestions to the symptoms. Vacuum leaks do not cause a car to stall under acceleration load and fail to restart for some number of minutes.

 

[RustyRatRod]

Read, learn, diagnose, repair.

I cannot agree more. Not speaking about the OP here, but SO many people want it handed to them on a silver platter and being online, that's usually impossible to do and pretty tough in person. SOME level of diagnosis is required and almost no one wants to do it.

 

[slantsixdan]

Not speaking about the OP here, but SO many people want it handed to them on a silver platter and being online, that's usually impossible to do and pretty tough in person. SOME level of diagnosis is required and almost no one wants to do it.

…so sometimes they go Reading and learning sounds boring and slow; why should I bother with that when I've got a bunch of people telling me exactly what part to replace? I'll just pick one of those I think sounds nifty and do that. They waste money and time, their car doesn't get fixed, and they learn nothing. The sun sets that afternoon in the West, and rises the next day in the East. ¯\_(ツ)_/¯

 

[KosmicKuda]

I posted this in the Carb Woes post so this is kind of a repost but the title of this one says stalls under load/30mph. Note that the FSM says problems could show up between 15 and 30 mph.
*******
I was just looking at a 1973 FSM and it flat out says that if there is excessive throttle shaft wear in body then the carb should be replaced. Period. No other discussion.
But the 1968 manual goes into further detail: "During manufacture, the location of the idle transfer port and the spark advance control ports to the throttle valve is carefully established for one particular assembly. If a new shaft should be installed in an old, worn body, it would be very unlikely that the original relationship of the ports to the valve would be obtained." It affects operation between 15 and 30 mph.

Wow, that's enough of a condemnation for me , among others, to start looking for a BBS over the winter. Maybe a 60's vintage. There's been a lot of complaints about how rebuilt parts are a crap shoot these days. Alternators, carbs, starters, etc. FSM's go into great detail about carb adjustments. What are the odds that a mass rebuilder takes the time? Could be a good indoor project for you over the winter though.

 

[volaredon]

Thought he was running a Holley 1945
I've had those rebushed before and worked fine

 

[zmarty27]

Thought he was running a Holley 1945
I've had those rebushed before and worked fine

My thoughts exactly. Not a power making machine by any means, but it'll run fine with a few replaced gaskets and a float adjustment. I set my floats kind of high and I felt a noticeable difference in my take-off. Still hitting 0-60 in a whopping 9 seconds, though. LOL

 

[74DartSwingerCapeCod]

Get a rebuilt Carter. New fuel filter, maybe an electric fuel pump. Bypass or delete all emissions garbage. Adjust the valves, and adjust initial timing to 5*- 10* BTDC. Check to be sure the vacuum advance is good. That thing should run like a champ.

 

[74DartSwingerCapeCod]

Hoping someone might be able to help me with my next query…

I have to admit that I’m hesitant to pose the question for fear of another sidetracked discussion relative to reading versus research and/or what I will or will not enjoy, complete or be able to afford. That’s just impolite ego unchecked.

I’m no dunce, but I’m not a mechanic. I am however trying to learn to repair a car which holds sentimental value for me. I know the difference between reading and research just as well as I know the difference between a knowledgeable person with a bad attitude and a knowledgeable person comfortable and secure enough to help another… to understand that we sometimes arrive in the same place for different reasons.

In short, I’m asking questions to those willing to help. I’m not enduring anything resembling a disparaging attitude from anyone. If you forgive my ignorance in your area of expertise, I’ll forgive yours in mine.

Heres my question:

Bought a NOS Carter BBS for 73 Dodge truck. (Weber carb no is in the 6xxx series, I don’t have it with me)

I’m wondering if this is a non emissions carb with fewer vac ports that I’ll be putting on a 74 Swinger with emissions equip that won’t have anywhere to plug in.

Put another way, I see a thousand hoses. This BBS got enough holes?

If so, advice? Anyone who can walk me through what I might encounter so that I might gain a better understanding prior?

I continue to pore over every diagram I can find comparing the current Holley 1945 to the 73 truck BBS.

You likely understand what you see, Im trying to.

Again, I welcome your advice. I have no time for your disrespect.

Thanks

Gregg

 

[SixPaksRule]

please check the timing chain for stretch and check if the timing has jumped - The experts here should be able to help you
Slantys have weak timing chains

 

[Tims 66 Cuda]

Im late to the conversation, but is this carb model the one with an inspection plate for the metering rods. If so check the adjustment those things were a pain in the arse back in the day. Just my .02

Tim

 

[pishta]

Dunno, sounds like fuel
Starvation to.me. when your car dies immediately check the bowl for fuel if you have to take it off so be it. I had similar symptoms when my fuel pump went south. It would start and idle just fine, take it for a spin and it would wheeze , lose all power and die. would start up fine in a minute and idle again only to lose power and die again under load. I had an electric pump so my symptoms would be slight different than yours but sounds like fuel to me, and now a dirty carb after it sucked the bottom of the tank. even a new carb can pick up a nugget or two and plug something important

 

[slantsixdan]

Hoping someone might be able to help me with my next query…

Yup.

I have to admit that I’m hesitant to pose the question for fear of another sidetracked discussion relative to reading versus research and/or what I will or will not enjoy, complete or be able to afford. That’s just impolite ego unchecked.

Oh, sorry! I didn't mean to answer your question completely and correctly like that, with all those links to relevant information, after you specifically asked, by name, for my advice. And I especially apologize for answering your question about the Carter BBS before you even asked it. That was really disrespectful of me; I'll take a seat now. If you want me to take down the offending post so your hurt feelings can heal up, just say the word and I'll zap it for ya. Sorry.

 

[slantsixdan]

I've had those rebushed before and worked fine

Yup. When a brand new carburetor could be had for $36.57, "throw it away and get a new one" was sound advice, but we don't live in that world any more. There's no reason why a throttle body rebush can't result in a carburetor that works as well as a new one—if it's done skillfully and carefully.

 

[RustyRatRod]

Yup. When a brand new carburetor could be had for $36.57, "throw it away and get a new one" was sound advice, but we don't live in that world any more. There's no reason why a throttle body rebush can't result in a carburetor that works as well as a new one—if it's done skillfully and carefully.

Even better than "a lot" of new ones.

 

[RustyRatRod]

Hoping someone might be able to help me with my next query…

I have to admit that I’m hesitant to pose the question for fear of another sidetracked discussion relative to reading versus research and/or what I will or will not enjoy, complete or be able to afford. That’s just impolite ego unchecked.

I’m no dunce, but I’m not a mechanic. I am however trying to learn to repair a car which holds sentimental value for me. I know the difference between reading and research just as well as I know the difference between a knowledgeable person with a bad attitude and a knowledgeable person comfortable and secure enough to help another… to understand that we sometimes arrive in the same place for different reasons.

In short, I’m asking questions to those willing to help. I’m not enduring anything resembling a disparaging attitude from anyone. If you forgive my ignorance in your area of expertise, I’ll forgive yours in mine.

Heres my question:

Bought a NOS Carter BBS for 73 Dodge truck. (Weber carb no is in the 6xxx series, I don’t have it with me)

I’m wondering if this is a non emissions carb with fewer vac ports that I’ll be putting on a 74 Swinger with emissions equip that won’t have anywhere to plug in.

Put another way, I see a thousand hoses. This BBS got enough holes?

If so, advice? Anyone who can walk me through what I might encounter so that I might gain a better understanding prior?

I continue to pore over every diagram I can find comparing the current Holley 1945 to the 73 truck BBS.

You likely understand what you see, Im trying to.

Again, I welcome your advice. I have no time for your disrespect.

Thanks

Gregg

I haven't seen any disrespect. Maybe some car guy ribbing. The post you speak of has given perhaps the most information as all the rest combined. It's not our jobs to powder your butt and tuck you in at night. We're car guys. We're smartasses. We're also a family. We poke fun, we recognize stupid questions (none of yours were) with the poke of a stick. We're glad to help, but if you get your feelins hurt, that's because of your perception, not because of our conveyance. I don't think there's anyone here who will blatantly be disrespectful of a member without provocation. My advice is, rather than look through the forest of great information to find the one blade of grass you think is an "insult" is to concentrate on the forest. An optimistic outlook is always best.