And now after a short test drive, it feels like the accelerator pump has now ripped....again. take off from a stop sign and it sputters and dies. Checked pump flow once at home again and it now only spits all the way through the stroke.

I have a show to go to tomorrow with this car so I'm going to try the 1920 again. Only reason why I thought it was running too rich was because my mileage dropped when I put it on. Looks like I'll be hoping that the mileage drop was just due to mis adjusted timing.

While I have the 1945 off, looks like I will be examining that accelerator pump bore to see why now the 4th one has ripped....

3874598 was used with carbs that had full manifold vacuum? Check timing with hose off. Whats the carb number? Still have plastic float? Too heavy? Get brass new one. Slots are for duration of pump stroke. This 1945 should have rod with a u shape bend for length adjustment. Changing that length will have affect on tip in sag. One last thing ,that's an air bleed carb I think. Fuel level too low will make lean out. Its late going to bed.

I will get the carb number next time I go out to the garage. It does indeed still have the plastic float. Being that the car had sat for such a long time, it would nt surprise me if it has eaten some gas and gotten a tad heavy. I was told this was the original carb to the car, but I have no way to prove that. I have noticed that tightening the "U" bend in that rod helped a little bit with the tip in sag. Not much, but a little.

Dan - I performed the exhaust blockage test you recommended using the vacuum gauge. While operating to 2,000 rpms, vacuum gauge dropped straight to zero with no hesitation. I guess this rules out any major blocks in the exhaust system.

After bolting on the 1920 carb, acceleration has greatly improved. No more sag on take off and the gas doesn't stink like gas anymore (must've been the bad timing). Looks like I'll be running a complete tank of gas through this one to see how it does mileage wise.

Really hoping to get this car to 23-25mpg!!

You're not meant to watch for what happens when you snap the throttle open, you should look for what happens to the vacuum reading at a steady engine speed.
That's going to be difficult.

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

I figure that if it already gets 19 then I should be able to at least get to the 20's easily. 25 would be an optimal scenario basically.

19 MPG from a slant six is a pretty amazing feat. 23-25 on a stock naturally aspirated slant six is virtually impossible on anything but a downhill slope with a tailwind. If you doo manage it, please keep a careful log of your miles travelled and fuel consumption and pos the specifications of your build.

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Casually looking for a Clifford hyperpak intake for cheap.

By all means go for it, but two things: (1) Don't be disappointed when you don't reach your 23-25 goal; that is a heavy, underpowered, undergeared car. And (2) keep careful track in advance of how much $$ you're spending for your MPG improvements. Yes, it's possible to rework that car to get much better mileage and driveability all at once, but it requires things that take huge amounts of work and big chunks of cash money (fuel injection, overdrive or 4-speed manual trans swap, etc).

I think probably the №-1 reason why the 1920 carb is giving you better, less gaspy driveability is its distributor vacuum setup as hinted at by matv91 and provided in tabular form in his thread here (first page, last post). For my own experience in comparing ported vs. manifold vacuum spark advance on my '73 225 Dart, read here.

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

I agree with Dan, the mileage you desire is going to take a lot of work to achieve. The gearing with a heavy car is working against you on initial takeoff from a light or a stop sign. The more throttle you need to get the car moving the less mileage you will achieve. My '75 Dart is very similar to your car. It has a 225 (with a 1945 carburetor), a 904, and a 2.76:1 rear gear. I have extensively worked over the distributor (multiple spring changes, welding the advance slots, and multiple resizing of the slots) to attain the best initial and mechanical advance for my combination. All the testing was done on the road and/or in a controlled environment of a chassis dyno. Once the initial and the mechanical advance worked well, move on to the vacuum advance. The vacuum advance tuning can take a tremendous about of time to achieve optimum tune for your application.

After all this work, I have been able to average just under 22 mpg for the last 2.5 years. Additionally, my speedometer reads slow by approximately 2.07% over the entire range 10-70 mph. So with the variance added in, the slant would be slightly over 22 mpg. The best mpg I have achieved has been 24.7 mpg. If your plan to drive your car in the winter (cold weather), you mileage will drop greatly.

Another thing I cannot understand is your accelerator pump diaphragm constantly tearing. I have worked on many 1920 Holley carburetors, and I have yet to see one tear during normal driving. I wonder if there is a serious adjustment failure leading to the problem or if there is an installation error.

From all the testing I have done, a 66 jet in the Holley is going to be too rich for any type of decent fuel mileage. The 66 jet resulted in an a/f ratio of about 11.4:1 at cruising speeds on our test vehicle. You need to lean out the a/f ratio a bunch to achieve any decent mileage.

So can 23-25 mpg be achieved? Possibly, but not overnight, it will take a serious amount of time. A single tank of fuel will not provide any results as to what adjustment worked or did not work.

The torn accel pump and № 66 jet are in his 1945 carb, not the 1920 he swapped on.

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

Dan that was some good reading. As the chart shows, my vacuum advance is hooked up to manifold vacuum. However, my vacuum gauge shows that even at idle, the line down to the dizzy has no vacuum signal till I tip into the throttle a bit, so it shouldn't be activating the advance till I'm on the go pedal anyway.

And yes, the number 66 jet and messed up accelerator pump are on the 1945 that's now on the shelf. Been through 4 of them now. Maybe it's set in such a manner that it's rising too far out of the bore and tearing while going back down into it? I'm stumped there. The stroke feels fine when worked by hand, however it feels like the center of the bore is almost too loose to tightly fit the rubber pump in. You feel some resistance through 60% or the bore, then it gets loose for maybe another 30%, then tight till the bottom.

That suggests potentially a non-original carpotater. Be interesting to see what numbers you find on the 1945.
Could be. Could be poor-quality parts, too, or a casting flaw or corrosion in the pump cylinder.

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

Finally got the carb number. 3870923 is the number on the side of the bowl. Hopefully that's the right number![/img]