So the snail won the drag race...

[Dave145]

Hey guys back again with this demonic Dart. 4 door all original car, 37,000 miles, bone stock featuring the 225, 904, 2.71:1 rear combo.

Let me start out by saying its slow. Not the kind of slow you get when your fingers are drenched in tar and you want to text your grandma, but slow as in molasses in alaska in january kind of slow. And the best part? MPG's kinda suck too. Step on the gas, and you're greeted by...nothing but the gas gauge dropping.I currently get about 19 mpg. Doesn't matter if i drive it in the city traffic, idle in a parade, cruise the highway, or pray to jesus, it gets 19.

I've rebuilt the Holley 1945 so many times I know it by heart. Every passage cleaned, gaskets matched to the tiniest pin holes, screws tight but not ape-**** tight, done.
Came with a 61 jet. So lean it died if you looked at it wrong.
Tried a 64. Better, but leaned out so bad on the highway it was ridiculous.
Currently at a ... 66! And it still feels lean. I don't have access to a wideband to know for sure.

Accelerator pump works very well and shoots a nice healthy stream of go juice with every stroke. Gas doesn't drip when it's parked, gnomes don't steal my gas when I'm sleeping, and the lines and tank are solid. I'm out of ideas for the carb. Drill out the idle transfer slot a bit to richen the mixture without the accelerator pump for take off maybe?

Other than that, timing is set to 18* BTDC. High as the dizzy will let me take it.

Newer plugs, wires, cap, rotor. New tires properly inflated. All fluids changed religiously. Only guess I have for lack of power is bad vacuum advance unit, unless someone smarter than me has a suggestion.

But really, 19mpg AND the ability to give the tortise a gold medal in a race?

I'm not interested in dropping in a 318. All original car that's unmolested...gotta be an unwritten rule against that somewhere. Low mileage engine too. I run 93 octane gas and drive 55-60 on the highway too if that helps.

 

[slantsixdan]

More info, please. Is it a '74, '75, or '76? Federal emissions, California emissions, High Altitude emissions, or Canada emissions?

First thing to do is stop flushing your money down the crapper with high-test gasoline. This car will run just fine on regular unless the engine is badly carboned-up and/or you've got it badly misadjusted (which you have; 18° BTDC is not an appropriate ignition timing setting and it's working against you).

There are probably some simple and inexpensive adjustments and reconfigurations you can make to improve things dramatically, but can't provide a useful list without year/spec info.

 

[Dave145]

Sorry Dan forgot all the different emission packages. Alright here goes.
- It's a '76 with federal emissions.
- Catalytic converter (PO installed) is newer.
- About 5,000 miles on a tune up - plugs,wires,cap,rotor
- Being a '76 it has factory electronic ignition
- Pulls 21" of vacuum while idling at 750rpm

Honestly I've tried lower timing. 12* you'd accelerate faster walking. I tried installing a Holley 1920 carb once to see if it would be better, and even though it had way too large of a jet in it and ran rich, it actually fet like it gave the car some power from the driver's seat.

 

[needsaresto]

Well,a multi spark ign may or may not improve the gas mileage.I did make a home made water fogger system and installed it in my Grand Caravan,it used windshield washer fluid. Mileage did improve by about 10% .Synthetic fluids in everything would help some too,even wheel bearings.My good friend here has built several hydrogen generator/boosters for many of his cars.He has made the local paper several times. This absolutely works in a non computerised vehicle,not only will your mileage improve dramatically,but you will see a noticeable power improvement and also a huge drop in emmisions..A computer programmed vehicle will see a lean condition and dump in more fuel to compensate,doesn't work.
Heres a good example of a working booster.

http://www.free-energy-info.com/Smack.pdf

It's easy to make,and I based my more simple water fogger on it.

 

[AJ/FormS]

Ok here we go
#1, check the exhaust pressure,
#2, compression test. In this case I would do a Leakdown test too.
#3, set the valve lash if you have solid lifters
#4 If you changed the lash, redo the compression test
#5, Check the balancer TDC mark, that it is true and correct
#6 make sure the crankcase is not overfilled with oil!
#7 If the carb was designed to run on fresh air and manifold heat, make sure those systems are working properly. Most of those carbs I have seen were designed and calibrated to run with a constant temperature of air. If you defeat this system prepare to spend hundreds of hours re-engineering your carb, or buy and older, non heated-air, model carb.
#8 The vacuum advance can is designed to help your engine get better fuel mileage. Make sure yours is working. It can be worth 2 or 3 mpgs, on a good running engine, and about ZERO (or less!)on an over-advanced slug .
If you have a lean-burn system the computer controls all timing changes via the computer mounted Vcan. If it is defective, you will have a slug, for sure. I shoulda probly made this #1.

1)To check the exhaust pressure, you will need to braze a short length of brake line into the pipe (about a foot long), somewhere after the manifold and before the cat. Wherever is convenient. Then plumb a low pressure gauge, 0 to 10 psi, to that steel line so you can read it in the cab. Then you go for a roadtest. Drive the nuts off it, and make note of the highest reading, and also the steady-state cruise reading. The steady-state should be less than about 1.5 psi, under 1.0 is better. The WOT/full load at peak torque(around 2400rpm), should be less than 3.0, and hopefully under 1.5 is best.
If the numbers are bad in front of the cat, you will have to repeat the test between the cat and the muffler. If these numbers are also bad, change the muffler first. But if these numbers are good, get rid of the cat.
2) to make power you need 165 psi. If you are under 110, no wonder it's a slug. As to a LD test you are looking for less than 4%. At 8% no wonder it sucks gas.
3) mine likes .013/.023, at ambient temp.Yours may vary. Just make absolutely sure it is not too tight. And be sure your feeler fits between the rocker arm and the valve tip, without touching anything else;look very very closely. False clearance adjustements are all too easy on slantys.
5) you will need a special tool for this called a piston stop.

Once these tests are done come-on back

 

[slantsixdan]

- It's a '76 with federal emissions.

OK, that helps.

Catalytic converter (PO installed) is newer

Newer than '76, that's good...how much newer? Many of the aftermarket converters on the market are junk, and most of them are not up to the task of cleaning up the very dirty exhaust from a nonfeedback-carbureted car like yours; they can easily overheat and melt down internally, causing severe exhaust restriction. More info on what to buy in a good and capable converter on request. '76 was the last year for the way-too-small exhaust headpipe; for '77 they finally put a 2-1/4" headpipe on the six-cylinder cars which uncorked their breathing even with a stock-type muffler (speaking of mufflers, if yours is old, even with low miles, it very well may have collapsed baffles inside—that was one of the causes of your same symptoms in my '73 bought with 44k original miles).

About 5,000 miles on a tune up - plugs,wires,cap,rotor

Good (assuming good quality parts were used). But that 18° BTDC ignition timing setting means your carburetor adjustments are also going to be way out of whack. Eventually you're going to want to get everything set up so your base timing is 5° to 7° BTDC. Recommend you contact DusterIdiot over on slantsix.org, who is a wizard at setting up well-curved SL6 distributors.

Being a '76 it has factory electronic ignition

Yes. A "multi-spark" ignition won't do much but drain your wallet and reduce the car's dependability, but consider the HEI upgrade .

Pulls 21" of vacuum while idling at 750rpm

Also good. Still, how long since a proper valve adjustment was done?

I tried installing a Holley 1920 carb once to see if it would be better, and even though it had way too large of a jet in it and ran rich

...and acted like a blowtorch on the catalytic converter...

it actually fet like it gave the car some power from the driver's seat.

The first few years of Holley 1945 were notoriously poor runners. A 1920 is a few different steps backward. Really, the desirable and effective induction improvement is to go to a 2bbl, which tends to not only improve driveabilty and performance but also fuel economy.

Pull and plug the vacuum hose off the EGR valve; that'll considerably reduce the mushiness of acceleration. Check if your distributor vacuum advance hose runs directly from carburetor to distributor with no stops in between; if not, make it so for another large improvement in driveability. While you're paying attention to the distributor vacuum hose, give it a hard suck and cap it with your tongue to see if it and the advance pod it's connected to actually hold vacuum.

Sooner or later you're going to want to check the cam timing. Slant-6s of this era often came through with severely retarded cams, which make the engine into a gutless wonder no matter how you adjust things or what bolt-ons you install.

There is nothing such as "free energy", and so-called "hydrogen booster/generators" (also "Brown's Gas", "HHO", etc) are a lame scam that only make sense to those who can't (or won't) understand basic science. The human mind has vast power to fool itself, but not vast enough to break the laws of physics, no matter what some yahoo on some website claims. Keep your eye on the ball; the task at hand is to figure out the cause of your car's sluggish acceleration and fix it—save the tinfoil for kitchen tasks; there are way better hat materials out there.

And in the end, take note that the '76 6-cylinder engines were weak and the '76 Darts were heavy and undergeared; these cars were sluggish even when new and as perfect as Chrysler could manage to build them at the time; you are probably looking at some carefully-thought-out upgrades to get the car to where you want it.

 

[pishta]

My friend over at slantsix had a dog with a 170 /6. he dropped a 225 in thinking it would help. turns out he had a Cordoba 8.25 2.24 rear end in it! That car would downshift going up a driveway.

 

[slantsixdan]

Chrysler really kinda went backwards with rear axle ratios. The lightweight early A-bodies with torquey non-smog engines would've been much nicer to drive and got much better mileage if they had 2.76 rear gears instead of the 3.23s and 3.55s and 3.91s(!) they came with. The later heavyweight cars with weaker desmogged engines are a lot nicer to drive with 3.23s.

 

[Dave145]

I'm hoping to keep the car as stock as possible on the 1bbl induction system and mopar ignition. I'll make it a super six if I really need to, but also being low on dough it may be harder to accomplish that!

The cat was installed about 10 years ago according to the receipt. I don't know the brand since a shop did the work. At that time she got new exhaust all the way back including the muffler. Stock tiny pipe size though.

I do not honestly know when the valves were last done. PO was a mopar guy too so I'd like to think he set them but...I can't be sure without a set of feeler gauges. It's really quiet while running for and engine with mechanical lifters though.

When you mention retarded cam timing, can I just drop in a new timing set like on a Ford to fix the retarded nature of them?

I disconnected the EGR a long time ago. It was the only way I could get the car to accelerate from a stop without falling on its face and dying.

 

[slantsixdan]

Tiny exhaust pipes + 10-year-old cat (meow!) moves exhaust restriction higher on the list. If you wish to address this in the best possible way, your headpipe should be 2-1/4" diameter and you should put in a cat (meow!) equal to the task being asked of it. Yes, you can buy a cheap little converter very easily. They are junk, warranted only for 25,000 miles and minimally effective even on clean-burning engines. But for a nonfeedback-carbureted vehicle like yours, you need a heavy-duty, high-load converter -- anything less is a waste of time and money and will quickly need replacement again. The trick here is to get a California converter. These have to be type-approved to much stricter regulations that require much longer durability, so you get your money's worth in the long run. The one to buy is this (that's a very good price on it, too -- might want to pounce on it before the price goes back up, and put it on your shelf for when it's time to install). Another good idea while the converter's being installed is to wrap the headpipe with this, which will do several good things: it will keep the exhaust extra-hot on its way into the converter, which facilitates maximum converter efficiency and reduces the likelihood of converter damage by improper fuel/air ratio. Also it keeps the underhood temperatures cooler, which is beneficial for driveability.

"Really quiet for an engine with mechanical lifters" suggests the tappet clearance may be too tight, which will take a big chunk out of engine performance.

Just dropping in a new timing chain and sprockets, lining up the dots, is a big gamble. The location of the dots isn't anywhere near as exact as we wish it were. You really(!) want to take the time to degree-in the camshaft. Given the car's configuration you'd benefit from advancing the cam from its nominal position, and you'd benefit even more from an RV10-RDP cam swap, (big wakeup for a stock or stock-ish \6).

If you want to keep things as stock-looking as possible, keep your eyes open for a NOS Holley 1945 for a Dodge truck application. Those have bigger venturis and are generally less strangled. Take your time and wait until you find a genuinely new one; "remanufactured" carburetors are junk. And do get with DusterIdiot about a recurved distributor.

But if you're on a super tight budget, you may well just have to stick to the easy low/no-cost stuff like a careful valve adjustment and tip-top careful tune-up and live with the nature of the beast until you can afford to "re-nature" it more comprehensively.

 

[AJ/FormS]

I've had really good results with single barrels.Older singles seemed better, but the one on my 1980 Volare was fine.

 

[needsaresto]

Well,call it what you want. Im not going to argue. Real worl results in my freinds car put it at better than 45 mpg from a 305 built in the mid 80's...Yes theres no such thing as free energy,but there is such a thing as increased efficiency.

 

[slantsixdan]

Sorry, no. 45 mpg from a 305 plain and simply flat did not happen -- not on this planet. The most likely explanation for such a figure is your friend's inability to do arithmetic correctly, combined with a whole lot of gullible wishful thinking.

 

[Dave145]

Where I'm from (southern Wisconsin), my car is emission exempt. If I don't need a cat, I'll gladly delete it all together. Exhaust pipe size I figured needed to be stepped up a bit...waiting to get a few more dollars before doing that for now.

I've recently replaced the thermostat with a 180° one for the summertime. Sure the car runs cooler, but it definitely ran a lot better with the oem 195° stat in.

Good info on the carbs. I'll keep my eyes out.

I'll try and get a feeler gauge and someone with experience to show me around on there to adjust the valves at some point.

What are the average tuning points for these motors? Most common jets to run, most common amount of timing (I've heard folks say they run upwards of 14° or as little as 4° with good results), etc.

I wil check the vacuum advance unit and weights in the dizzy. Just signed up at sl6.org so I will get in touch with dusteridiot soon.

Anything else I should be looking for here? What mpg numbers SHOULD I be seeing from this car?

 

[slantsixdan]

Where I'm from (southern Wisconsin), my car is emission exempt.

Then if you wish, delete the cat (meow!).

I've recently replaced the thermostat with a 180° one for the summertime. Sure the car runs cooler, but it definitely ran a lot better with the oem 195° stat in.

Put the 195° stat back in.

I'll try and get a feeler gauge and someone with experience to show me around on there to adjust the valves at some point.

Step by step guide at valve adjustment article.

Most common jets to run

Highly variable carb-by-carb.

most common amount of timing

Goal is to get the distributor set up such that you have 5 to 7 degrees BTDC base timing.

Anything else I should be looking for here?

Well, again, you're going to want to check your cam timing. Probably not much timing chain slop with that low mileage, but it's very easy to check (pop off the distributor cap and rotate the engine by hand with the fan and fan belt in one direction til the rotor starts turning, then the other direction til the rotor starts turning; you want minimal/zero delay between turning the engine the second direction and the rotor beginning to turn).

What mpg numbers SHOULD I be seeing from this car?

In perfect tune, a dead-stock '76 Slant-6 Dart driven conservatively at sea level will return about 15 city/20 highway.

 

[whitepunkonnitro]

Check that the flapper in the exhaust manifold is not stuck in the closed position.
Had a valiant with all your symptoms, and that was the ticket.

 

[Dave145]

I'll check that flapper valve whitepunkonnitro.

Really only 15/20? Wow would've guessed higher for some reason. I have a vacuum gauge at home I'll use to check the vacuum advance tonight. What are your thoughts on drilling out the idle transition passages in the carb? I have a few articles detailing that and it sounded like it returned great results.

 

[needsaresto]

I've been in the car...more power as well as that gas mileage.It aint wishfull thinking,it's documented.

 

[whitepunkonnitro]

I've been in the car...more power as well as that gas mileage.It aint wishfull thinking,it's documented.

No question that it is possible with a car/combination and driving style that is dedicated to MPG.
I've seen stuff like this before.

 

[slantsixdan]

Right, now here comes all the fine print. 45 mpg out of a 305 with tires inflated to 60 psi, not exceeding 20 mph, coasting down hills in Neutral with the ignition switched off...that's believable. Anything near 45 mpg with anything like normal driving of a 305: nope.

But right, right, sure, it's got tons more power and gets triple its original fuel economy at 70 mph uphill with the A/C on, all because of an amazing hydrogen generator that doesn't actually do anything like what is claimed. This is no different than those Russian peoples who live high atop mountains and have a reputation for living to a hundred and thirty five years old, mostly because they can't count correctly. From here the conversation goes to pointing out that the world's automakers would immediately adopt anything that would give them even a tenth of that kind of improvement, immediately followed by a bunch of whispering about how Big Oil and Big Auto bought up the rights and suppressed it because blahbitty blah conspiracy blah blah.

It's documented, you say? Great. Show us the documentation.

 

[DNasty777]

Don't give in Dan! This is a really good trouble shooting thread so far!

OP, sorry I can't help but your original post did give me a chuckle!

 

[Dave145]

Well guys, here's where I'm at. Vacuum advance unit is good. Put a vacuum gauge on it, holds 18in of vacuum without any leakage. With my timing and my light set both to zero, full advancement on the distrubutor's vacuum advance brought the balancer around almost all the way back to zero again. Set the timing to 5* BTDC and set the carb. Now 19" of vacuum at 750rpms in park. Took her out for a drive and already noticed an improvement. And a rather large one at that. I know there's more to be had out of this motor, so now I'll be checking into the rest of the things mentioned.

The heat riser though, is something I'll question. Is it a bi-metallic spring that controls the flapper? Reason I ask is this: When cold, it stays closed both idling and when applying throttle. When warm, it's closed at idle still however it now opens (though kinda sticky) with a blip of the throttle. Normal operation here correct?

Next areas I'll be visiting will be the exhaust, in which the whole system is still pretty much spotless from when it was put on. Since cash is on the tighter side, I may just cut the cat out and replace it with a piece of straight pipe and some clamps.

If I stab the gas from a standing stop, the car has a delayed response. Kind of like it has to catch up with itself. Accelerator pump set to maximum aggressiveness already as well. Again I'll reference the idea of drilling out the idle transfer slots...good idea or not?

 

[slantsixdan]

Well guys, here's where I'm at. Vacuum advance unit is good. Put a vacuum gauge on it, holds 18in of vacuum without any leakage.

Good...take note that these vacuum advance units are adjustable, so it's going to make sense to map out your advance vs. vacuum levels. First step is to mark your crank pulley in 5-degree increments: put the timing mark at 0 and apply a dab of white or other bright-colour paint to make it stand out. Rotate the engine so the mark is at 5° BTDC, then put another dab of paint (a different colour, if you like) at 0. Rotate another 5 degrees and make another mark at 0. Keep doing this until you have 8 marks (totalling 40 degrees). If you use different colours it will be easier to read, but you can do it all in one colour as long as you keep track of which mark is which. Then you set your basic timing to zero and with the engine idling you gradually apply vacuum to the distributor, taking notes on how many degrees of advance you get per inch of vacuum applied, until you don't get any more advance.

You can use the same marks to map out your mechanical advance, too: disconnect the vacuum advance, hook up a tachometer, and take notes on how much advance you see at 500-rpm intervals. You don't really need to go above 3500 rpm -- assuming it has a tire size in the neighbourhood of P195/75R14, and with the 2.76 gears, your engine is turning at just 2180 rpm at 60 mph in 3rd gear, 2543 rpm at 70 mph in 3rd gear, and 3160 rpm at 60 mph in 2nd gear. Which gets us to two other points:

-That vacuum reading indicates a basically healthy engine. But the fact you could get away with 18° BTDC without massive pinging suggests a problem such as sluggish or frozen mechanical advance. You've got an old, low-miles car on your hands; it's entirely possible the distributor's advance mechanism is stuck with old grease. Lack of mechanical advance, together with a working vacuum advance, could easily cause or worsen your slow acceleration and gaspy floor-it behaviour.

-You'll be wantin' to check the cam timing. With that kind of super-low-RPM operation, it's probable you'd be quite a lot happier with a dollop of extra cam advance.

With my timing and my light set both to zero, full advancement on the distrubutor's vacuum advance brought the balancer around almost all the way back to zero again.

Tilt! This doesn't make sense. Typical amounts of advance the vacuum can is capable of are between about 13 and 32 crankshaft degrees.

Set the timing to 5* BTDC and set the carb. Now 19" of vacuum at 750rpms in park.

That's a good reading and good settings.

Took her out for a drive and already noticed an improvement.

Yep.

The heat riser though, is something I'll question. Is it a bi-metallic spring that controls the flapper?

Yes, but it doesn't work the way the pre-1971 types did. Those were heat-on until they warmed up, then heat off. The '71-up type with the large round weight has greater spring tension toward heat-on when cold, lesser spring tension toward heat-on when warm, and no spring tension only when well and truly hot. (there is nothing such as "closed" or "open" on a Slant-6 heat riser like there is on a V8) When cold, if you rotate the weight counterclockwise and let go, it should spring briskly back clockwise all the way to the stop. If not, hit both ends of the shaft with Chrysler 4318039AC, which is not at all like Liquid Wrench or PB Blaster or any of the other common penetrants. It is made specifically for this application and does an unbeatable job of it.

Next areas I'll be visiting will be the exhaust, in which the whole system is still pretty much spotless from when it was put on. Since cash is on the tighter side, I may just cut the cat out and replace it with a piece of straight pipe and some clamps.

That might improve matters somewhere between a bit and a lot, depending on the condition of the cat (meow!).

If I stab the gas from a standing stop, the car has a delayed response. Kind of like it has to catch up with itself. Accelerator pump set to maximum aggressiveness already as well. Again I'll reference the idea of drilling out the idle transfer slots...good idea or not?

Not a good idea, no, at least not right yet. This kind of modification is at a level to be done only by highly skilled and experienced carburetor tuners. It's never a cookbook matter of "Drill [passage] with a [size drill bit] and everything'll work great"; trying to do it that way is an almost surefire way to spoil the carburetor and cause new problems.

The gaspy behaviour you describe is not abnormal for the mid-'70s cars. It'll take careful tuning and tweaking to improve.

Also: a 3.2 rear axle ratio would do wonders for this car's driveability, quite aside from improvements made to how the engine runs.

 

[barnett468]

ajforms and whitepunkonnitro have made good suggestions.

vacuum advance has zero affect on acceleration . it should be set to add around 6 degrees of advance if your timing curve is set to the optimum level for your particular engine.

advance it 5 more degrees than stomp on it and see if the hesitation has improved . its highly unlikely that it is the accelerator pump.

post a photo of at least one spark plug

19 mpg is very good for that car . i wouldn't be complaining.

 

[slantsixdan]

vacuum advance has zero affect on acceleration

That's only correct if you mean full-throttle acceleration. It's wrong if we're talking about part-throttle acceleration, the kind most of us do most of the time.

it should be set to add around 6 degrees of advance if your timing curve is set to the optimum level for your particular engine.

There are a bunch of good reasons to disagree with this apparently random, blanket 6-degree figure.

19 mpg is very good for that car . i wouldn't be complaining.

This part's right.