I agree it's a fuel problem. I would have fixed the left turn problem with the 1920 carb, as I'm familiar with it and think it's a better carb. I've had two slant-sixes and had them both running beautifully when I was done with them.
I'm in Taunton, have full set of tools including vacuum gauge, timing light, dwell/tach meter. Do you still have the 1920?
Don't replace it, these motors are great and bulletproof and can be made to run well and with decent power.

 

1) Replace fuel filter
While doing that, do a crank with the filter off to see that the pump is giving adequate fuel.
2) check carb inlet for debris restricting needle valve.

 

Bob is on it. You may have a fuel pump problem. Any hesitation when opening throttle suddenly is accelerator pump. Super Six carb was a patch when the 1bbl was downsized in 74, 73 larger carb makes the same power as the 2bbl. So, stay with the 1bble, but the 73 carb will give it slightly more power. EGR on that model isn't very useful, if you don't have emissions inspection for function block it with a solid gasket. Bypassing the OSAC is certainly a good move. There was also a thermal valve in the radiator for vacuum advance which should be bypassed. 73 distributor may have better advance curve, do NOT advance timing past the stock 2.5 degrees.

 

My 1980 Volare with the slant 6 had a very similar issue After checking all the usual suspects I concluded that the original carb was messed up. Time being what is is today I bought a remanufactured one and after a short period of adjustment it now runs just fine.

 

I'm going to go in a totally different direction and ask if you've checked the flapper valve in the exhaust manifold for proper operation. I don't know why, it just popped into my tiny, little damaged brain.

 

I've had that stuck on two slant-sixes. All it does is subtly steal a little bit of power and make it warm up just a little longer. Nothing obvious.

 

Agree with some of the others that it seems to be fuel related. I would get someone familiar with using both a fuel pressure gauge and a vacuum gauge. Check the fuel pressure AND volume of the fuel pump, and using the vacuum gauge tune the carb mixture for highest vacuum at idle. Would also look at getting an earlier year carb as was mentioned, and if you don't want to deal with an electric choke, you could always go old school and rig up an under dash cable for a manual choke you can control yourself. I know you mentioned putting in a new fuel pump when you resurrected it from it's long rest, but lately I've seen more CRAP replacement parts that were bad new out of the box. Even seen a new coil heat up and short out. You can chase your tail for hours and days on stuff like that, thinking it can't be part xxxx, I just replaced that with a new one not long ago. PITA. Good luck.

 

Stalling on turns was common when the plastic float got heavy and began to sink.
There was a recall to add a baffle to diminish fuel slosh in the bowl. Some cars stalled under heavy braking and that was considered a safety issue. These were rich-stalling or flooding issues.

The mixture screw(s) are only for idle mixture. Their adjustment won't affect highway speed operation much when you are driving with the main metering system. The screws should be turned-in to 'just before a lean-stumble'.

The Holley 1920 gave way to the Holley 1945 around the 1973 emission year. Both will work as long as the fuel line, throttle and choke linkages attach correctly.

 

Thanks to all. Bob, I send you a solo"conversation" with my email, considering we're not too many miles apart. Let me know if you're ever down the Cape. Meanwhile, will take the advice and trace the fuel line back next. Plan to replace pump & fiter, check carb inlet. Looked inside distr, looks pretty clean in there, so doubting it's the pick up coil, but ordered a new one just for kicks. Vac advance exterior looks just a little grungy, not bad, from minor valve cover seepage. Once those items are replaced, I'm thinking we've narrowed it down to the carb, either the current 1945 or a 1920 I have if the bowl float prob can be remedied (left hand turn stall) I'll also check the air filt housing flapper just above the exhaust heat hose. Narrowing it down! Thanks for your help. Btw, here is the Dart.... really clean.

 

Good looking Dart. Years ago I had a brother with a 71 Fury with a 318. It would die on him when making a sharp left turn and ended up being a broken motor mount allowing the engine to shift and pinch off the fuel supply. My Dad figured that one out. I doubt that's what's up with yours, but you might check them just for the heck of it.

 

If it was diesel i would say that it leaks air in on the suctionside.
- this typically leads to a shutdown under load and is quite difficult to find if it doesent leak fuel at the same time.
Change all hoses on the suction side.

 

Probably not relevant, but gasoline in the 70s did not have ethanol in it. I had a lawnmower that would fire up and run and shutdown after 5 minutes. Turns out that the ethanol was causing a rubber hose to swell and reduce the gasoline flow such that the amount of gas used exceeded what the hose would flow. Just a thought.

 

Swollen gas lines could very well be the culprit, good thought.

 

Hi Allpars,

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 [I should have my mouth washed out with soap for using such terms] emissions crap? Such as vac amplifier etc? (Osac has already been routed to bypass air cleaner housing straight to distributor)

b) heard the carter (or is it weber?) bbs is a better simple hassle free carb than the holley. Will a 300 dollar expenditure be worth it?

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

Hi Allpars,

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 [I should have my mouth washed out with soap for using such terms] emissions crap? Such as vac amplifier etc? (Osac has already been routed to bypass air cleaner housing straight to distributor)

b) heard the carter (or is it weber?) bbs is a better simple hassle free carb than the holley. Will a 300 dollar expenditure be worth it?

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

The air cleaner heater could be stuck causing an overheated carburetor. The fuel pump could be bad. The manifold heat riser valve could be stuck overheating the intake manifold. The fender mounted ignition module often causes similar symptoms, too!

 

While i stuck heat riser is a problem they usually shows up at prolonged idle, at wot they are just lowering the output by a small number.

 

it's not about restriction, it's about over heating the carb and boiling the fuel out. But I can't be there so let's hope someone's suggestion helps🙂

 

Stupid question, but have you checked your vacuum advance on your distributor? I know I'm not a mechanic, but I'm trying to think outside the box here.

 

Vacuum advance is off at idle, not a factor.