They probably did increase the jet size to compensate for the primitive first-year EGR system. Bypassing the EGR and OSAC will have made a significant improvement, not a reduction, in your car's efficiency and MPG.

Jets are available, but can be difficult to find locally. You may want to contact www.carbsonly.com and see if they'll offer you a reasonable price on a #56, a #57, a #58 and a #59 jet, purchased at the same time as a carb rebuild kit, replacement float, and a couple of extra bowl gaskets. That way you will have everything you need to experiment with different jet sizes and see what happens with mileage and driveability.

What spark plugs are you running?

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

Dan,

It is a 612 jet, stock jet. Yes, a looser lash does help the mileage and I fill up every two days and have the records to prove it.

I get jets from our local auto parts in town. You can order through Summit or Jeg's as well.

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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

Sometimes, but not necessarily. It depends on cam timing and other factors. And, I repeat, the difference between 0.010/0.020" and 0.012/0.022" is not 2 mpg, nor anywhere close.

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

The plugs are Champion RN14YC, gapped at .035".
They look brownish/light tan.

The factory spec is N14Y, gapped at .035".

I don't know how N14Y is different from RN14YC, though.
I replaced the plugs with the same as what was already in the engine when I got the car.

I removed the spark plug gaskets. I think you're the one who gave me that tip, Dan.

By the way, bypassing OSAC and EGR definitely helped the engine from a performance perspective, not so much an economy perspective. If it is supposed to help engine efficiency, the performance is where I'm seeing it. I definitely think the car is safer this way (i.e. ability to accelerate and keep up with highway traffic). It might hurt the emissions a little but I'm not going to worry about that.

OK, you're not running grossly rich, then. For reference, you can do much better than Champions. Next time you replace the plugs, use NGK number ZFR5N. It's a special extended-tip spark plug that improves driveability and economy, and it's of much higher quality than the Champions. Whichever brand of plug you pick, you were right to remove the metal ring washers before installing the plugs. Keep doing that.
R = resistor
C = copper core
The two are inseparable. If you take advantage of the improved zip, mileage won't increase.
You're right.
Not so much. These primitive emission controls were designed to squeak the cars past Federal emissions certification testing so the cars could be sold new. Their effect in the real world is primarily to make the cars run poorly.

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

OK.

Dan, you suggested checking for slack in the timing chain.
Looking at the rotor for a reference, if I move the fan all the way back to take up the slack, and take a measurement on the belt, and then move it all the way forward to take up the slack again, there is 5/16" of slack.

I don't know how this translates to the timing chain, if there is really 5/16" of slack there also or not. I also don't know what is acceptable.

I'll try switching to the spark plugs you suggested.

I guess I'll start by getting a new float, if for no reason than the one I have is original. It's not flooding, but hey, it can't hurt. Then maybe I'll try using a smaller size jet. The ignition stuff seems OK to me.

I understand using EGR on these cars, but OSAC? It doesn't seem to do anything but make the car soooo slow!

The way I check timing chain wear is by rotating the crankshaft by hand back and forth at the vibration damper. There is a certain amount of drag mainly due to friction of the piston rings against the cylinder walls, and a considerably larger friction when the timing chain slack is taken up and any further rotation in that direction will turn the camshaft. This is quite easy to do by feel. Measure the number of degrees of crankshaft rotation at the timing mark, how much you can go back and forth without turning the camshaft. There is a procedure for measuring timing chain wear in the FSM, however, the timing chain cover has to be off to do this. I used trigonometry to convert from the FSM method to my method. The factory allows up to 9 degrees of crankshaft motion before timing chain replacement is recommended. However, in my opinion, the factory spec is too great. I recommend replacement at 6 degrees. A new timing chain & gears set should allow less than 2 degrees of crankshaft rocking motion. On the mopar small block V-8, the timing chain will usually jump teeth at 12 degrees of slack. The slant six can stand more wear than the V-8 without jumping, but replacement according to my recommendation will result in a better running engine, well worth the time & expense.

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1964 Dart 225 1966 Valiant 225
1966 Dart 273 1966 Barracuda 273
1969 Dart 225
'64-170 engine '66-170 engine
(two) 198 crank/rod sets in custom-fitted wooden boxes

wooden motor scooter with hybrid-electric drive

OK, I will try to figure out the number of degrees of rotation then.

What I basically did is turn the fan (and therefore the vibration damper via the fan belt) while watching the distributor rotor for when it just started to move. I took up slack in one direction and made a mark and then took up slack in theother direction, and masured the distance.

The 5/16" measurement is the amount the fan belt would move before the slack was taken up.

I don't know how many degrees that translates to but I'll find out.

It seems like a lot to me, but the car does run amazingly well the way it is.

OK, assuming you took care to make sure the belt moved exactly how much the engine moved (no slippage of the fan pulley under the belt), hthat indicates there is some slack in the timing chain. Without knowing exactly where on the belt you saw this 5/16" movement (crank pulley, fan pulley, alternator pulley, somewhere in between?), it's not possible to provide a precise translation into degrees, but an estimate can be made by looking at the spacing of the degree marks on the timing tab. With 5/16" slack, you could be looking at 3 to 5 degrees' cam retard, which could certainly drop your average mileage by the 2 to 4 mpg you've experienced.
It got the cars past Federal NOx emission standards...EGR wasn't enough!

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

OK. I checked for the degrees of rotation on the vibration damper.
I would say it's about 6 to 7 degrees of slack in the timing chain.
So, I guess it's within factory tolerances but it's still a fair amount of slack.

The 5/16" of slack I measured up by the alternator pulley.

By contrast, my 225 Dart, which has had it's timing chain replaced a few years back, only has 4 degrees of slack in it.

So I guess that's it as far as my mileage goes. Well, I don't know that I'll be replacing the timing chain just yet just for that, but it was good to narrow it down and know what is working OK on the car and what's not.

Factory specs (9 degrees' slop) are a joke. You're due for a T-chain on your '73. It's not likely to stop running any time soon, but you should add the project to your to-do list.

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

Newport77,

Tuesday night when I cam home from work, I did dome trials with different jets again. Last time was about 9 months ago.

Using the Aussie carbon fiber intake gasket, no manifold or exhaust leaks anymore, this is what I found. 52 degrees, 78% humidity
#55 is driveable but the lean surge is very obvious. You end up on the power valve very quickly.
#56 is much better, but the lean surge is still noticeable.
#57 seems like a good compromise, no lean surge at all and fair power just on the jet, without dipping into the power valve cruising.
#58 is fat, very, very nice lots of power seldom dipping into the power valve at all, just on take off and passing.
#59 is rich, tons of power.......

So if it will be awhile before you change the timing chain, try dropping down from that 61 jet to buy you some mileage in the mean-time. I actually ran a 59 for a few days and the mileage dropped 2.5 miles per gallon. It was kind of fun though. It had an excessive amount of power. I could easily pass 3 or 4 cars at a time on the back roads.


I am back using the #57 since it provides a significant mileage gain and if I need to pass 3 or 4 cars, it just goes into the power valve, and I am gone.
My carb has a dual plunger circuit so it delivers twice the fuel compared to the single plunger circuit.

The mileage jumped back up to 23.5 to 24.5. It depends on not passing too many cars on the back roads.

_________________
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