OK, I have tried at least 12 different carbs. Some junk yard specials, some remans, and some rebuilts of both the 1945 and 1920 variety. It seems I cannot get one to perform properly under all conditions. One might cold start well but not run well warm no matter how it is adjusted. Another might not cold start without ether but run great when warm. I have adjusted to specs and tinkered with them but cannot get one to run well all the time. My latest is a 1920 just rebuilt and adjusted to specs. It is almost impossible to cold start and when hitting the gas, it nearly dies. Don't know about mileage yet. I also wonder about the specs my under hood tag has for a 73 Duster (knowing the engine block is 1980 with hydraulic valve train and 81-83 heads). Those specs say idle speed of 750 rpm and timing at TDC. I know from this site that timing should be 10-15 range and the lowest I can get idle is around 1,000 rpm. Is there some secret combination of timing and carb adjustments that works? What have y'all found for the best way to adjust these beasts to get good running under all conditions and good mileage? Thanks in advance for the advice.

Mike

Adjusted to what specs?
ALL original carbs work just fine hot or cold.

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Have you used a vacuum gauge to trouble-shoot the problem?
It sounds like a late transition into the power circuit, that is a pump shot timing or "economizer valve" (power valve) adjustment.

Is the distributor's vacuum advance coming in at the correct moment? You may need to adjust that.
DD

I adjusted the carb to the specs in the carb rebuild kit as far as the choke closure and pull off. I had adjusted the distributor vacuum can to be more responsive as weel. Perhaps I need to go more? I also have the pump set at the middle hole on the linkage per the rebuild sheet. Disn't see any economizer adjustment on the 1920. I agree they should all work regardless but it is strange that I can put a different one on and it works exactly oppostie the previous one. Using a vacuum meter, what should I check for? Also, what is the appropriate idle speed and timing? Thanks for the help.

Mike

Ill be watching this one as I carefully rebuilt a BBS to specs on this site and cant get the car to run warm without closing the choke flap to 1/4". I cant enrich the mixture.

BTW, please dont use ether... it's hard on the engine.

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I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

my 77 supersix{2 barrel} w manual choke ,will not run right w the choke fully opened, so I am constantly pulling or pushing the manual choke to various locations to keep it running strong{depending on weather and any other factors.

The power valve is supposed to adjust the mixture as the load changes by varying the depth of a tapered needle into a jet as the vacuum changes. Do you know if the power valve needles are free? Perhaps the springs are bad that lift them. On the BBD 2 bbl they are adjustable. That carb is perhaps your bet. I wonder if the vacuum passages to the popwer valve are working.

I am not sure what the power valve is. I know the acelerator pump moves and I know there is a small plastic piece that the economizer moves that affects the position of some small steel balls inside. Can you please describe a bit more what I need to look for? Thanks.

Mike

The economizer valve is just another name for power valve, does the same thing. I don't believe you can adjust it, just replace the plunger that makes contact with the plastic lever in the meter block.

I replaced it as part of the rebuild. Is there any possibility that the problem could be timing and/or mixture? I am unable to get it to idle at the specified 750 rpm also. Thanks.

Mike

Do you know what you idle vacuum reading is?
A vacuum leak, retarded cam or ignition timing or tight valve lash can all reduce the vacuum signal.
The carb. operates off of manifold vacuum so if the signal is weak you will have problems.
As for adjusting the power valve, on a Holley 1920 you can adjust the "economizer valve" by adding shims between the spring and the base of the plunger.
DD

I haven't measured the vacuum and I am not home until Friday. Do I put the gauge on the port to the distributor advance? Also, what should the readings be? What do I use to shim the economizer valve and does increasing the shim give a better response? It sounds like the shim will increase the power of the spring since it goes betwen the spring and the plunger? Sorry for all the questions but I have been messing with various carbs and settings for months and have not been satisfied with performance. Thanks.

Mike

I forgot to mention, it can't be valve lash since I have hydraulic lifters and I have checked for vacuum leaks numerous times with none found and my timing is set at 15 degrees. Don't know about the cam timing and where it is. What is weird is that one carb can have a great cold start and acceleration but eat gas and idle bad. Another won't cold start or accelerate but idles warm real well. That would indicate that the problem is in the specific carb as opposed to other engine issues?? Or am I missing something else? Thanks.

Mike