Im running a 500 cfm Edelbrock and I had to detune it it get the optimal mixture. I only figured this out after installing a wideband O2 sensor kit. The motor did run with the carb stock but it was slugish in town.

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~Nic

thanks DusterIdiot...I've just ordered the Dave Emmanuel book, will give it another shot...if I still have no luck I'll look into the edelbrock carb.
thanks for the guidance..

Dusteridiot-......the adaptor plate you have, is it aluminum or plastic?...read the reviews and one states the aluminum ones retain heat and cause poor restart, but more complaints about the plastic ones warping...any suggestions?

It's not an adaptor, it was a carb spacer...I used aluminum so it wouldn't warp or crack like phenolic...it's not going to conduct any more heat than the manifold...and you are going to install taller studs and sandwich it between a set of gaskets that will insulate it....

Much of what you mentioned is over my head. The carb on the car is a rebuild done by me and honestly one of my first attempts. So it may very well be that it was not done properly.

I will take this info and reconvene with my minions who have more experience and have been assisting me with this build. I appreciate your input. this is what makes this forum such a plus by giving access to the knowledge and experience of people that I would never have the chance to meet otherwise..Thank you

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3sped6, a ways back: I'm going to guess that you are running rich when on the main jets with that 60 jet covering up improper accelerator pump shot, and or a vacuum leak.

You need to get the above mentioned book, I had to read it over and over until his message sunk in. One has to understand the four stages of fuel delivery and transition between them, enrichment, and the roll vacuum signal plays to be able to achieve good drivability and economy, otherwise one is shooting in the dark.

Also take a look at this site. Until I installed an o2 sensor, I was lost in the weeds of power valves, jets, and acc. pumps for a few years. That sensor enabled to get a very good tune absent of flat spots, stumbles, poor fuel economy, and stinky exhaust at idle in a few hours of fiddling around.

Another device that can cause stumbling is incorrectly adjusted accelerator pump arm. Pump has to initiate its delivery of makeup fuel to cover temporary lean condition the instant the throttle is opened. Any gap between arm and contact with throttle linkage will cause a stumble particularly during cruse dipping in to throttle approaching a small incline, or on flat ground.

Holley TV on Holley site has tips on how to select a power valve.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

ok...so Ive installed the 390 and have been fiddling with it while reading the holley book. While Ive learned tons, I still know very little.
Ive got the car running and can detect no vacuum leaks (although ive been told my symptoms suggest a vacuum leak). at cruising speed she runs fine, no lag, no hesitation, but at idle, cant seem to get a good idle under 1000 rpm, and when I drop it into drive, the engine stalls unless I feather the gas peddle, then the car shakes. Once going I'm in good shape. I had 50-52 jets (pri-sec) and have found 70-72 seem to function better, although reading Dusters comments, this is a band aid fix. I have stock exhaust, but will be replacing that with 2-1/4" within the next few weeks. (will that have ANY effect on how it idles??..I cant see it helping but figured Id ask)
My vac at idle -1000 rpm- is about 16', my compression is 95-98-94-103-101-98 (1st to 6th)

any suggestions where to go next?
thx in advance

Yes, those are classic symptoms of a vacuum leak. I would pull the manifold and look to be sure that each port made an impression on the gasket. Carb to adapter and adapter to manifold should also be checked.

Any more than 4-6 jet numbers change with a mild combination like yours and you're masking the real problem.

That's not very good compression if checked warm. Trying to tune a worn engine will have you chasing your tail.

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Joshua

Isn't spraying ether judiciously a better first option for vacuum leaks? Not sure though how risky that would be on a hot exhaust manifold on a slant. Others wish to comment? Removing a manifold to visually check impressions seems drastic at this point to me.

I suspect a gross vacuum leak. The kind that doesn't respond well to normal checks with carburetor cleaner, ether, etc. I would check the intake and exhaust flange thickness as well to be sure that the intake manifold is thicker than the exhaust. If the opposite is true (thicker exhaust manifold flange) the intake clamp load will be very low and the chances of a vacuum leak very high.

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Joshua

A few thoughts:

My Holley 390 drove me nutz, same symptoms as yours; wouldn't idle well below 1000 rpm. I received numerous posts that I had a gross vacuum leak, but had done all one could do to find the problem. My head had a fresh rebuild with trued up gasket surfaces, and manifold was also trued up.

The problem was the base of the carburetor was warped, its bolt hole ears were deformed from previous over tightening causing the base to become concave. The test for this is to use a straight edge such as the ruler part of a machinist's combination square placed on base in east west, north south, and the two diagonals with a bright light directed to back side of straight edge to illuminate any gap under it.

My gap was so great that one could not spray enough on base to reduce the leak; it was sucking from all four sides.

If you find this problem:

To correct this problem use a #10 or #12 mill bustard file (file has to be stout enough not to deflect, and course enough not to easily plug with aluminum filings). File in the same axis' as tested above until all cupping is removed. Most of the material removed will be from the four eyes and base where eyes attach.

One more thing:

Where you converted this carb from 4160 (vacuum secondary) to 4150 manual secondarys) there will be a vacuum leak from the internal passage that operated vacuum diaphragm that needs to be plugged. Also the secondary throttle plates when at their stop may be letting in too much idle make-up air from mal adjustment causing the idle circuit to go lean. Also the linkage connection primary to secondary has to adjusted so that the secondary throttle plates don't flutter or lift off the stop at idle. The books you have address this adjustment.

One test you can perform for secondary flutter is to hold secondary throttle plates closed with your hand and observe any idle quality change; this means they are being held open by mal adjusted linkage, binding in bore from worn throttle shaft or other reasons.

Chances are good you have several causes adding up to the idle problem that need to be winnowed out one by one.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

WJAJR

omg, that sounds EXACTLY like my problem..I figured a new carb was in store, but that gives me some hope...thanks for taking the time to pass that on to me