I'm a little slow with carburetors so I need help

[ryanb73]

Hi everyone.  Despite owning a lot of carbed vehicles, I have yet to be much good with them.  I am running a stock '76 New Yorker 440 long block (for now) with a Mopar Performance single plane spreadbore manifold and an Edelbrock Performer 750 carb, with the spreadbore to squarebore adapter.  Timing is set to 8 BTDC.  My engine is running like crap, idles rough, is fouling plugs (black carbon), and the exhaust smells rich.  It also has low vacuum (about 10mmHg).  If I turn both idle mix screws all the way closed, it still runs with no apparent change.  Am I wrong or is that not supposed to happen?  This intake and carb combo have 0 miles and the carb is one of the factory remanufactured ones.  I did check for vacuum leaks but can't seem to find any.  If anyone has some tips for this specifically or even just carb tuning in general, I would be very appreciative.

Ryan

[71chally416]

No way it should even run if the throttle lever is in the right position and you have the mixtures screws all the way closed. Did you have to open it way up to get it to stay running?

[ryanb73]

Nope, didn't touch the throttle, just kept idling, although it is a slightly high idle, probably around 1000-1100rpm cause it dies if you drop it to 500-600.

[71chally416]

So the throttle position is just as you took it out of the box? You didn't have to screw the idle speed screw clockwise at all to get it to idle?

[ryanb73]

Oh no I have played with the idle mixture and idle speed adjustments.  I just meant that when I closed the idle mixture screws all the way (as it was running) I didn't have to touch the throttle to keep it running.  I have increased the idle speed a little (probably less than 3 turns) from factory setting to get it to idle higher like that since it runs so rough and dies at low RPM.  But I haven't changed rods or step up springs or anything.  The only things I have played with are the idle mix screws and the idle speed.

[moper]

The intake is a total mismatch, the adaptor makes it worse. Just out of curiousity, do you have the factory intake? I would advise to install that with the adaptor and the new carb... As far as adjustments, if you sped the idle to 1000, you are no longer on the idle circuits, so it won't die of you close off the mixture screws. You need to get the stock intake back on, and then work on setting the carb. It should idle at 550-650rpm, and smooth. Also, there are different colored springs for the step up pistons.. Those are like the power valves in a Holley. You ned to order the strip kit for that carb, and follow the directions. I think you will need to change those springs once you have a usable intake on it.

[ryanb73]

Do you mean the intake is a mismatch to the carb or the engine (or both)?  I know a single plane is not the best for the stock low compression engine now, I have a forged crank motor that will get built for this car when I graduate.  Will this carb and intake combo work when I build that motor (shooting for somewhere around 400hp) or is it just a bad match?  When I bought the intake I forgot to make sure it was a squarebore and I am not real happy about the adapter.  For now you're probably right, I should just put the stock intake back on and keep the adapter.  For the future though, would I be better off keeping that intake and getting a spreadbore carb or selling that intake and getting a Torker II or something?  And to clarify you think the manifold (at least matched with this engine and carb) is responsible for the low vacuum and crappy idle?  Thanks for the input I really appreciate you guys taking the time to help a carb-challenged guy like myself.
Ryan

[acudanut]

 Running a 440 long block, as opposed to running a 440 short block ??
Seriously, you should use a Holley 750.  You will have Zero problems. Sounds like your choice of carbs is killing your plugs.

[Chryco Psycho]

Stock 440 Long block as opposed to running aftermarket or modified heads
 I agree the intake is a mismatch , a stock iron intake would work better
the intake may work with a future combo or you can use the Holley street dom later as well , the 750 will work with a basically stock engine though , I would go bigger later though , tuning could make the present situation better , more initial advance with the vacuum advance dialed out some would help , the idle mixture screws should affect the idle though so you may have an issue with the carb itself as it is now , float level may be too high which is the first thing I would check , also you may need to replace the springs under the metering rods if they do not stay down AT IDLE IN GEAR

[71chally416]

You can also try just bolting the carb right to the manifold. There should be enough sealing surface to seal a square flange carb if you use the right gasket. I suspect that speadbore adapter is leaking somewhere.   

[acudanut]

 True, lose the adapter first.

[71chally416]

Did I ever tell you guys about my buddy with the 70 340 Dart that knocked 3 10ths off his ET removing the 750 Holley he had when he bolted the very same 750 "refurbished" ED carb that this guy has that I had bought from Jegs? I never touched anything on it but the idle mixture screws. He refused to give it back and payed me full price for it. There's nothing wrong with ED carbs. The same type carbs were OEM on thousands of stock Chrysler vehicles, including the 426 Hemi. Just because they are made in the USA doesn't mean they aren't good. 

[ryanb73]

I hadn't thought of trying the carb without the adapter.  I will probably just put the stock intake back on and try it without the adapter, then if it will idle at a reasonable RPM, I can follow the tuning instructions in the manual for the carb.  Now I just have to find time to do it.  I am a veterinary student and have 8 classes this semester, ranging from radiology to surgery.  Thats why I haven't made a whole lot of progress with the car in the last two years.  Every time I get to work on it it has been sitting so long I feel like I am starting over!  Thanks for all the input guys I really do appreciate it.
Ryan

[71chally416]

I'd try removing the adapter FIRST. No reason that manifold should cause your problem. Might not be the ideal Intake for a stock motor but it should work OK.

[Roppa440]

As Chryco was saying, you need to match the metering rod springs to your manifold vacuum. They are easy to access and your tuning manual explains it clearly. With the low vacuum (which could be caused by a number of things) the metering rods will be up and making the mixture very rich.

Also if the throttle is open too far at idle you are not on the idle circuits at all. Which is why adjusting the idle has no effect.

There is no reason why this carb could not be made to work very well on this engine as long as the right manifold is used.