Stock 225 slant six in a 1973 dart with a two barrel carb set up from a super six. Car runs great but the gas milage is about 15 to 16 with 90% highway driving. This same setup was on my 65 Coronet getting about 20 mph so I am pretty sure that the intake setup is working fine.

After pulling out the little hair I have left trying to get better milage, I decided to check the advance cure on the dist. The engine was set to 0 degrees static timing, measured mechanical advance that developed 20 degrees, also the vacuum advance added another 20 degrees that came to a total of 40 degrees.

To the best of my knowledge this motor should be running a max total of 32 degrees. Am I right? Could the over advance be killing the milage?

Does anyone know how much advance should be vacuum and mechanical?

Any suggestions on engine tuning for milage improvement ?

Appreciate any help, need to keep what little hair I have left.

Well. First, double check for vacuum leaks.

Second, you will need to get a reliable vacuum guage and a dial back timing light. These are essential for tuning your distributor advance curve. Another very useful tool is a hand-held vacuum pump so you can check your vacuum advance and adjust it.

You need to spend some time mapping out the spark advance at different RPMs. Warm the motor up, disconnect and plug the vacuum advance line, set the base timing to 0, then record how much mechanical advance you have at every 100 RPM point above 600 RPM. You should have about 32 degrees total advance coming in by 2800 RPM.

We also need to know the number stamped on the distributor goivernor and the number stamped on the arm of the vacuum advance pod. These are critical to determining where your base timing should be set since these tell you howe much mechanical and vacuum advance each advance system will provide.

One thing to check is to make sure that the distributor springs and weights are still lubricated and the weights move freely. The grease can get dried out and stick, not allowing the timing to advance.

Once you have the mechanical advance mapped, post it and we can give you some ballpark recommendations. Also, post your rear axle gear ratio and type of transmission (auto, 3 speed stick, 4 speed stick).

Drive it with the vacuum gage and a tachometer hooked up. Make a note of hom much vacuum you have at you average cruising RPM. Your vacuum advance should be adjusted to start coming in at a vacuum reading a little bit below your cruising RPM.

Also, don't overlook fine tuning the carb. Have you adjusted the mereing rods? How about the choke? Have you checked if the choke pulloff diaphragm still holds vacuum?

I was able to get 20-21 MPG highway with a two barrel carb in my brother's 1983 Dodge van with a slant six. A 73 Dart should be able to do better.

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Casually looking for a Clifford hyperpak intake for cheap.

John B,

I have been running at 55 degrees total for the last two years after recurving the distributor. There are many ways to get there.

An example would be to run 12 degrees initial and 20 degrees mechanical and 22 degrees vacuum advance at 2500 rpm.

I personally run 16 initial and 16 degrees mechanical and 22 with the vacuum advance at 2500 rpm. This particular set up makes my engine feel very spunky and allot of fun to drive and it gets good mileage.

There is no wrong or right way, however you need to match the recurve to the engine build for the best performance.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

32 degrees would be 'tops' for mechanical advance, mileage is to be gained depending on build when in the 45-50 range mech + vacc. advance.

To do this methodically, you'll need to do what Reed has instructed, because you need base results of what it is currently running like.
Noting what mechanical components are in your dizzy will help
provide an idea of what we have to work with in getting the above results.

And yes you can kill power and mileage if you are over advanced, so while trying to get the 30-32 mech and 48+ mech and advance the 'curve' needs to be tailored so it just doesn't come all in and be too advanced at certain shift points or have the mech all in too soon (i.e. if you set it for being all in at 2800, and your gearing puts you at 3100 rpm at highway cruise it's a bit too soon....)

Things to think about,

-D.Idiot

Good advice so far, though you needn't necessarily buy a dial-back-to-zero timing light. You can use a regular timing light if you first mark your crankshaft pulley appropriately.

Speaking of which, have you verified that indicated TDC (on the crank pulley) is actual TDC? If the outer ring of the crank pulley has slipped relative to the inner hub, which can and does happen with age and use, then your timing settings and calculations will be thrown way out of whack.

Have you pulled and checked your spark plugs to see if the engine's running rich? How long since a careful valve adjustment?

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

Thank you for the replys. I guess that I am having a senior moment, still need more help.

At 2500 rpm I get full mechanical advance of 20 degrees. If I set the initial timing at 12 degrees that would give me a total mechanical and initial advance of 32 degrees.

Now on top of that the vacuum advance is good for another 20 degrees at full vacuum. Now when driving around the vacuum is less than full and thus the vacuum advance is less than full.

Is this the way to set it up?

Stock 225 cu in automatic running 3.23 rear end. Most of the time crusing on the highway I am turning about 2800 rpm.

John

That is one way it can be set up. To get a bit more in to the meat of the subject... with stock springs the 'true' mech advance will not be used since stock springs are a bit stiff (most are all in by 4400 rpm...)...
So if you do dial it up just like you proposed, just make note that if you decide to pass another car and run it up to 3500+ you may end up with more mech advance (but with the vacc. reading low due to throttle position...your total advance may be less).

I would work into that kind of number slowly... advance it 5 degrees, set...test... check plugs... take note, as in change your timing your fuel will also change (more advance = lean, less advance will make things a bit rich), so you'll need tomake sure your carb settings will handle the changes.

And double check as Dan says... nothing like having your readings off and wondering why it pings badly.... ("Hey I fixed the damper, is 66 degrees of advance too much?)

good luck,

-D.idiot

Yeah, but base timing advanced that far can eat into driveability and fuel economy, as well as creating ping problems. Better to get the distributor set up so you can run a base timing of between 5 and 8 degrees or so.

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

john b,

Yes, your on the right track. The distributor vacuum advance pod is driven with ported vacuum, not intake manifold vacuum. The vacuum would start as soon as you crack the throttle and be the lowest closed at idle and at wide open throttle. If you want to measure the ported vacuum, you can install another gauge on the distributor vacuum line to see what the vacuum advance pod is seeing. Others on this site have listed the various vacuum advance pods made through out the years and tables for how much advance they apply at different vacuum settings.

So driving down the road the amount of advance the vacuum pod applies varies with the throttle position. A vacuum pod stamped with 11R on the arm would give you the extra 20 degrees.

Looks like we all posted about the same time. Heed Dan's advice.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG