My slant runs smooth both on cold starts and after choke releases but if I try to remove the air cleaner while it is running, it dies. All vacuum hoses are connected and in good condition, timing is set to tdc with vacuum advance plugged. New plugs, wires and air cleaner filter. Carb was rebuilt just before I bought the car. I took it off and checked the float level and it needed adjustment but that didn’t help. This is a 1966 225 with a Holley 1 barrel. Any ideas?

What is your vacuum reading at idle?

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Casually looking for a Clifford hyperpak intake for cheap.

Vacuum leak somewhere

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63 Plymouth Valiant Wagon

18 lbs steady

What’s your theory?

The engine can pull good vacuum and still be to lean to run at idle.
Is the choke vacuum pull-off leaking badly?
PCV valve stuck wide-open?
Idle circuit in the carb plugged?

Will the engine run if you partially close the choke flap, with the air cleaner off?
DD

I'm thinking the air filter is excessively restrictive and is causing rich running that is compensating for another problem. When you remove the restriction you uncover the preexisting problem.

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Joshua

I concur with Doctor Dodge and Joshie225. You have a carburetor calibration problem being masked by a restrictive air cleaner.

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Casually looking for a Clifford hyperpak intake for cheap.

So let’s try it this way. No air cleaner installed, hard to start, won’t idle, will run if I hold the throttle open to a high rpm. Since I can’t find a vacuum leak, something in the carb is not functioning properly. Idle circuit feeds fuel, air comes from the bleed port But both are clear. What other air source could be plugged?

Checked choke pull off and it is good.
PCV is good
Since it will idle smoothly at 500 rpm with the air cleaner in place , I would guess the idle circuit is clear? Otherwise I don’t understand where the fuel is coming from to keep it running.
I don’t mean to sound “short” about it but this one has me stumped. Next step will be to shell out the money and try another rebuilt carb. I don’t know who built this one, po told me he had just had it rebuilt.
Thanks for the ideas.

Holley 1920... correct? (not a 1945?)

It is more likely that the fuel feed for the idle circuit is partially plugged or leaking internally.
Try removing the idle adjustment needle (screw & spring) at the base of the carb.(count the turns) then use spray carb cleaner, with the red tube, to "power spray" / back-flush that passage.
Re-install the screw and see if anything changes.
DD

You can also try plugging the emulsifier air bleed to see if that changes anything.
This is the small brass port opening you see when looking down the carb.
Use a wire size that mostly fills this hole and secure the other end of the wire to be sure it does not get "sucked-in" when the engine is started.
DD

Holley 1920
Thanks, already did the backflush, no change.

Thanks, I will try that tomorrow and reply.

Old mechanics trick use your hand to choke off the air going into the carb if it smooths out it has a vacuum leak the air cleaner has the same effect.

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63 Plymouth Valiant Wagon