Holley 1945 Questions

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Aaron65

Aaron65

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I'm running a '74 225 from a Charger in my '65 Dart, and up until recently, I was running a decent Holley 1920 on it. Unfortunately, the casting on the metering block for the power enrichment arm wollered out, and is no good now.

So, I rebuilt the 1945 that came with the engine, and I've got a few questions. It had a 63 jet in it. Using my wideband, I've found that it cruises at around 15-15.3:1, and is in the 13.5-13.7 area under full throttle. Under light to moderate acceleration, it leans way out to 16-16.5:1 and stays there until I back off again. I can obviously feel this as a slight surge when accelerating.

The idle mixture screw also is backed out to 3.75 turns out from seated to get the lean-best idle.

The engine has 18.5 inches of steady vacuum at idle, and I have set the idle to around 725 RPM.

So, should I jet this thing up even more? It likely is the '74 version of the carb, which doesn't seem to have a good reputation.

Thanks for any insight or input...My gut feeling is to throw a 64 jet in there and see how it reacts, but changing jets in a 1945 is a little more of a pain than in a 1920.
 
If the issue is the surge under light accleration, I would;
- check vacuum under that condition; if in the 6-7 in range, I would expect the power valve should be coming in there and perhaps the power valve linkage or piston is wrong or hanging

Also, I would re-check the float level; this can really effect the carb under these condition.

IMO, if I was going to change the jet, I would go up 2 sizes......

Follow this link to slantsix.org and you will see another link for a Chrysler training film for the 1945. It is pretty good!
 
nm9stheham said:
If the issue is the surge under light accleration, I would;
- check vacuum under that condition; if in the 6-7 in range, I would expect the power valve should be coming in there and perhaps the power valve linkage or piston is wrong or hanging

Also, I would re-check the float level; this can really effect the carb under these condition.

IMO, if I was going to change the jet, I would go up 2 sizes......

Follow this link to slantsix.org and you will see another link for a Chrysler training film for the 1945. It is pretty good!
Click to expand...

I love those old training videos...I think I covered everything when it was apart, but I'm going to double check the power piston spring when I take the lid off. I can tell when the power system activates, because obviously the AFR enriches, but you have to have the pedal down over halfway before it does. I ordered a set of 64s and a set of 65s, so maybe I'll try the 65s first.

I found the same deal with my Corvair...having the AFRs where they are "chemically" correct equals worse driveability than when they are jetted a little richer than ideal. That's just anecdotal with two cars, but they incidentally both use one-barrel carbs (although the Corvair uses two of them). The Vair runs best two jet sizes above factory, even though cruise AFR at freeway speed is then around 14:1, and it's richer at lower speeds. Additionally, fuel mileage didn't seem to suffer much, probably because I didn't have to kick the throttle as hard to accelerate or get past the awkward points. It might be worth a shot to try it on the Dart anyway.
 
Have you checked your spark pulgs, wires, cap, rotor, and timing? Some mixture and combustion pressure combinations are harder to fire than others, and weak spark will show up more readily. The '74's initial timing is likely fairly retarded for emissions.
 
I'm actually using the '65 distributor set at about 7* initial. Dwell is within specs. I actually have a big old Sun oscilloscope, but I haven't hooked the car up to it yet. I may hook it up to my small primary oscilloscope just to check.
 
I pulled out my little Autolite spark plug scope. The plugs are actually borderline, so I'll throw a new set in, but I'm still going to jet it up 2 sizes to test it out.
 
I don't know what I was thinking before, but I pulled the carb lid off and the carb had a 621 jet in it. So I put a 64 in, and it accelerates smoothly without jerking like it did. So, so far, it's a success.

It'll probably be a little rich at cruise, but it should be good under wide open throttle and acceleration.
 
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