I've recently started having some problems with my '70 Dart. When I give it gas (from a dead stop or to pass), I get a drop in RPM and then it "catches" and I get power. I've played with the mixture screw to no effect, The air cleaner element is a new K&N, the automatic choke is working, the flap in the intake is working, no vacuum leaks, the carb is recently rebuilt..... I'm out of ideas. Also, I've been having some hot start issues. I did SSD's over-the-valve-cover fuel line mod, so I wonder if these problems are related since the mod is supposed to eliminate hot-start problems. I'm running a stock 225 w/3-speed auto. trans. Heat riser works, new plugs, new wires, points 6 months old and properly adjusted...... I just don't know. Thanks in advance, fellas.

Nat

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

With the engine off and warm, remove the lid from your air cleaner and peer down the carburetor as you manually operate the throttle. You should see a nice strong shot of fuel shoot into the center of the throat every time you operate the throttle. If you do not, there's something the matter with your accelerator pump (faulty components or improper assembly).

When you say the air filter is a new K&N, do you mean it's an open-element cleaner, or have you replaced the real filter element in the factory cleaner with a K&N element?

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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 replaced the factory element with a K&N element. I checked the throttle as suggested and I'm getting a healthy-looking stream of fuel when working the throttle cable.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

OK, so the accelerator pump is working. It may simply need to be readjusted to provide a bigger/longer shot of fuel; there is usually a large amount of adjustment available, depending which carburetor you're using. Then again, perhaps your power valve ("step up valve", "economizer") isn't working correctly. Does the stumble happen as soon as you step on the gas, or a second or two after?

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

It revs, then stumbles. It's a Holley 1920 1bbl. It's just started since the hot weather came to BC. about a week or so.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

OK, "Rev then stumble" is a classic symptom of a faulty power valve (which Holley calls the "Economizer"). This is the spring loaded plunger-diaphragm assembly that mounts under a potmetal cover held down with three screws at the left front corner, top surface of the bowl portion of the main body casting. You got a new plunger-diaphragm in your carb kit you used to rebuild the carb (did you do it yourself, or is this a purchased "reman" unit?). It's important to make sure when you assemble this that the rubber diaphragm isn't pinched, and that it's clocked correctly so that the through hole in the diaphragm and stiffener plate is lined up with the vacuum port in the carburetor body and with the port in the potmetal cover.

Down at the bottom end of the plunger-diaphragm is the hinged lever that actually opens the power valve, which is a spring-loaded bearing ball. Not only must the bottom of the plunger-diaphragm rest squarely on this hinged lever's arm, but the lever arm itself must also be in proper order. It's actually fairly easy to get the plunger-diaphragm unit in cockeyed so it sits next to the lever arm instead of atop it.

Some members have reported that the plunger-diaphragm units that come in the carb kits cause stumbling problems. Originally they are not all the same (different spring tensions), but in today's carb kits, you only get one choice. Sometimes it's the wrong one.

Other things to check: Did you properly install the float baffle? Did you weigh the float to make sure it's to spec? Did you set the float level correctly? Did you install the float counterspring under the float arm correctly?

Finally, note that the Holley 1920 is a persnickety beast. Sometimes they just throw these kinds of driveability problems at you and refuse to be (or stay) fixed no matter how often you rework them.

You know what I would suggest (replace it with a Carter!)

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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 had a mate rebuild it for me. He's been wrenching on /6 cars for years, so I thought it a safer bet than trying it myself. Is a carb rebuild kit the type of thing I can pick op at my local Lordco or Napa? Or is it a "track it down to the four corners of the earth item"?

Nat

P.S. Thanks for the prompt responses! I see I'm not the only one lurking about here all day long!

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Donno Lordco, NAPA sure has 'em, and if Lordco is a full-line jobber, they will, too. The quality of mass-market carb kits has been going down-down-down over the years, simply because of decreasing volume. It's getting to the point where it's worth paying the premium and waiting the delay to get one from an actual manufacturer rather than a marketer who shops 'em out to the lowest bidder. One manufacturer whose kits I've had good luck with is AFLA products. I've got their info around here somewhere...

But yeah, if you're hurrying, grab a kit at the parts store and see if replacing the diaphragm-stem assembly fixes it.

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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 new rebuild kit will be in tomorrow.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

Replaced the economiser diaphragm, checked fuel level in bowl while car was idling on a level surface, No help. I just don't know.

Nat

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!

See above:

... the Holley 1920 is a persnickety beast. Sometimes they just throw these kinds of driveability problems at you and refuse to be (or stay) fixed no matter how often you rework them...

Sounds like time for a different carb. A BBS for instance.

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

So, I re-replaced the economiser diaphragm - this time with the fuel bowl off to ensure it was seated properly. I also replaced the El Cheapo plastic fuel filter with a Napa Gold metal one, replaced the needle and seat and re-gasketed the fuel bowl. She runs as good as ever now! I wish I'd done the repairs separately so I could tell which one was the magic bullet. Thanks for the help SSD!

Nat

Grinning like an undertaker.

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1970 four-door Dart, 225/A-904/2.45 gears. 0-60 in twenty three minutes!