Hi everyone, first post here. I have a 1976 Dodge Dart with the 225, 904, 2.71:1 rear end combo. I have been referred here by Dan over at forabodiesonly.com on the topic of recurving my distributor. My motor is bone stock, but won't get out of its own way and only gets 19mpg. Here's what I have done to the car so far:
- recent tune up 5000 miles ago
- new tires properly inflated 400 miles ago
- 180* thermostat put in for summer driving.

When I got it, the PO had a shop install a whole new exhaust system 10 years ago. Stock size with the cat. (Not needed where I live so can be removed if needed). Carb has been rebuilt several times, intake gasket and choke replaced recently as well. 18* initial timing to boot.

My guess for some of these issues is possibly a faulty vacuum advance unit. Others have said to recurve the distributor. I have also heard of increasing the size of the idle transition passages in the car so it won't be so reliant on the accelerator pump.

Where do I begin? Many variables to play with here, would like to start in the right place.

Send a PM to DusterIdiot on here to get set up with an optimally-curved distributor. Shoot for 5° to 7° BTDC initial timing.

19mpg is good for a car such as yours, BTW, though it can probably be improved with thoughtful ignition advance maps and other upgrades, though you've said you don't want to swap to a 2bbl and cash is tight.

As recommended over on the other board: do a valve adjustment since you say your engine is very (suspiciously) quiet. Check the cam timing and check for timing chain stretch. Put the 195° thermostat back in for better efficiency, do the fuel line mod, consider the HEI upgrade and attendant wider spark plug gaps.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I would definitely work on the item Dan suggested...

I would use a hand vacuum pump and test the vacuum advance, if it doesn't hold a vacuum then that's a fairly quick and easy $18 part to get and replace.... given your post says it's at 18 degree initial says that might be a highly likely suspect....

If your distributor still has it's tag, getting the part number would help to see what would work best.

I can also recurve your distributor if you don't have the time/patience/knowledge.... PM me if interested...

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?

I'll check for the distributor tag tomorrow in the daylight. I've never done it before, but definitely not afraid to try with instructions and the right parts. Any way for someone to know the dizzy number based on just the application? Thought I saw something like that once....

Yes, I have the full spread of 1976 manuals...but if it's not the OEM distributor, it could be anything... Look for a tag screwed to the side , you may need a mirror and a rag to clean the grime off it... a good set of eyes and a bright light can get it if the tag is clean.

Before modifying the carb... look to see if your vacuum advance hose goes right from the carb base to the vacc adv pod, or if it's routed to an item screwed to the side of the air filter can... if so... get a true length of hose and make the straight shot from the carb base to the vacc pod...

What size in your tailpipe (1 3/4" inside, 2"... 2 1/4"?)

I also would advise keeping an eye out for a set of 2.94 or 3.23 gears or full 1973+ rear axle for your car... that will help get your car off the line better... (I will tell you... it was fun knocking down a poor kids ego a decade back... him and his girlfriend had a 1972 Valiant with the 318, 904, and stock 2.76 rear axle.... I roasted him by an entire car length with a 1974 duster in stock trim, 225 and 3.21 rear gears... he asked what engine I had... I answered truthfully, and you could see his girlfriend giving him crap about what he thought he had done to his
engine to boost the power, while I was looking in my rear view mirror...)


Now that you have timed things differently...drive it and see if that changes your mileage... then make another change... if you make too many at once you may not know what is working or is not...

Good...take note that these vacuum advance units are adjustable, so it's going to make sense to get that distributor number to DusterIdiot and/or 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.
Tilt! This doesn't make sense. Typical amounts of advance the vacuum can is capable of are between about 13 and 32 crankshaft degrees.
That's a good reading and good settings.
Yep.
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.
That might improve matters somewhere between a bit and a lot, depending on the condition of the cat (meow!).
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.

DusterIdiot's question about the vacuum advance hose routing is the same one I asked over on the other board. If the hose doesn't already run directly from the correct(!) port on the carburetor to the distributor, make it so.

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.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Sorry forgot to address the distributor vacuum line. It's hooked up from the base of the carb to the distributor. Nothing in the middle. Had some time this morning to dust off that tag on the distributor, and the number is 2875366.

Also before I just go hacking the cat out of the system, is there a way I can test it to see if it's restricted?

2875366? That's weird. That's a breaker point-type (not electronic) distributor for a 1968 B- or C-body with 225 and automatic transmission. Aside from the seven thick cables coming from the distributor cap, how many thin wires go to your distributor? One (directly to the (-) terminal of the coil) or two (with a black plastic pull-apart connector a few inches away from the distributor body)?

Exhaust backpressure can be tested directly if you have access to a threaded port in the exhaust pipe, but there's no such a port unless you make one. It can be tested indirectly by warming up the engine, hooking up your vacuum gauge to intake manifold vacuum, and watching the gauge as you operate the engine at a steady speed of about 2500 to 3000 rpm. If you see the vacuum reading gradually drop (less vacuum), that indicates exhaust restriction. However, this test tends to only show large restriction. It is possible to have restriction not severe enough to show up clearly on this test, but still enough to affect performance, driveability, and mileage.

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

Let me double check that number one more time. My guess is I read it wrong!

Good info on the vacuum test. Never heard of that before. I will try that at home tonight. Working out of my rather tiny and I'll equipped garage, that may be the best test I can perform at home.

Hey guys I re-read my tag this afternoon and realized I apparently shouldn't try to read dirty tags while I'm still waking up! Anyways, here is what my tag DOES say:
365
3874598

3874598 is very much more likely to be a '76 electronic-ignition distributor; I'll let DusterIdiot check his charts 'cause I can't find my '76s right now.

Now the $76,000 question: how'd you manage to come up with a '68 Slant-6 distributor number at random like that…?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

That comes to a mix of google and not reading correctly. I read 287somethingsomething86 this morning. Which was even more off. Then I googled a list of numbers for distributors and foun d a list on allpar. Re-reading that I now see it says for a '68 225 /6.

Oh, okeh. Because I was gonna say, if you could misread the distributor tag and happen to come up with a totally different 7-digit number that happened to also be for a \6 distributor, you'd wanna go buy lottery tickets.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I'll admit, the odds there would be very coincidental.