Carburetor question on old car...

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Sounds like the throttle opening is too high. I would adapt a junkyard 900cfm rochester quadrabog off a BB caddy onto that 460. You running stock "too mild" cam in that? where did the motorcraft carb go?


They never was a 900. Only went up to 800.
 
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As long as it's a vacuum secondary carb it's just a matter of setting it up right. The engine will draw what it needs at any normal operating condition. Bigger is never better on a street car, it's usually better to be on the smaller side to get better midrange response unless you like driveability issues.

And who here knows an Edelbrock carb is a Quadrajet? Or so close it doesn't matter. I've had blueprinted Quadrajets that flowed well over 800 cfm on a bench. A great design, poorly understood on the street.

BTW, I agree there is a LOT of terrible advice here. Among which is turning the idle mixture screws out to get high idle... it's IN to the high idle (lean) then out the appropriate amount, generally at least 1/2 turn. But it's all done by FEEL.
 
Originally Posted By: SteveSRT8
As long as it's a vacuum secondary carb it's just a matter of setting it up right. The engine will draw what it needs at any normal operating condition. Bigger is never better on a street car, it's usually better to be on the smaller side to get better midrange response unless you like driveability issues.

And who here knows an Edelbrock carb is a Quadrajet? Or so close it doesn't matter. I've had blueprinted Quadrajets that flowed well over 800 cfm on a bench. A great design, poorly understood on the street.

BTW, I agree there is a LOT of terrible advice here. Among which is turning the idle mixture screws out to get high idle... it's IN to the high idle (lean) then out the appropriate amount, generally at least 1/2 turn. But it's all done by FEEL.



I was always taught to use a vacuum gauge. Start with them 3/4 of a turn out, and go in or out to increase the vacuum reading until it is the best you can get.
 
You will find vacuum, RPM, and sound about equal in setting a carb's idle mixture screws.

Remember the mixture is going through different runners, with different end results for each cylinder. We are hoping for a reasonable compromise.
 
Thanks everyone for all the inputs! I spent a lot of hours this weekend trying to get it running right using a vacuum gauge. It still runs real rough and wants to die at idle. I sprayed brake cleaner everywhere I could looking for a vacuum leak, none found. (doesn't mean there still isn't one) Today when I get home from work I'm going to do a compression test to see what the condition of the bottom end is in. If the compression test shows good, then I'm going to send it to some repair shop in town that knows these old cars real well. btw, i'm still not convinced that 8 month old Edelbrock carb is not my problem.
 
Put a Holley on there
wink.gif
 
As much as I like to tinker, I have to agree with Overkill here.

A new or rebuilt carb in the box can solve a host of issues. But if you know a quality shop they can rebuild the existing one or at least help you tune it correctly.
 
Depending on your experience/skills, STeveSRT8 has a point.
You can do 80 things right in rebuilding a carb, but louse up one thing and it will not work right.
 
Take the top off the carb and check ur fuel float levels. Also u can remove the idle screws and blow some air thur them to clear out any dirt that might have gotten stuck in them.
 
To the OP's original questions:

You need both a vacuum guage and tachometer (old style mechanic's tach with dwell meter is best).

Once dwell is set, then set timing (with timing light, never by ear).

Now back out mixture screws only enough to get max vacuum reading.

Set idle to target idle RPM plus 50 RPM.

Close mixture screws until you lose that extra 50 RPM.

That's where you may be having trouble - you can't do this by ear. This is the "lean drop" method of setting mixture.
 
many years ago i made a jets and rods program for carter AFB. led you to calculate the change of jets and rods. its for a older program for a Commodore computer. right now iam having trouble with my e-mail. i would like to post my home address, but i know its not safe. i would like to give the jets and rods program to all my friends. but iam un sure as to how to do it.
 
Update - Compression test was good - readings ranged from 185 to 200, with only 15psi leak down after 4 seconds.

My neighbor drag races for fun - he offered to help. We pulled the plugs and they were all fouled, running too rich. We sandblasted and regaped them all. Then we put the original metering rods/springs in. (I had richer rods/springs in). Started it up, ran much better. Took it out for a test drive, all seemed good except for a stumble acccelerating off idle.

He said to buy the Edelbrock calibration kit and some new Motorcraft plugs. I picked those up yesterday. Last night we went one notch richer on the metering rod. That improved the stumble some. Then we went from the stock yellow springs up to orange, much better but still a small stumble. Went to pink springs and now it runs perfect! We checked the plugs when we were done and they don't indicate that's it's running too rich.

It was too hot last night to throw in the new plugs - that's planned for tonight. Then I'll drive it for about a week and then pull the plugs to see if it's running rich/lean.

Hopefully I have this licked - it's amazing what a friend with a fresh perspective can lend! And thanks to you all also for all the pointers...
 
Carbs have umpteen jillion adjustments and tweak points [plus tricks].
But every carb has it's own peculiarities.
No one knows them all intimately.
 
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